Quick answer

To contest a BIR deficiency assessment, act according to the document received:

Preliminary Assessment Notice (PAN): submit a written reply within 15 days from receipt. This is an opportunity to answer a proposed assessment, but it is not yet the formal protest required by Section 228.
Formal Letter of Demand and Final Assessment Notice (FLD/FAN): file a valid written request for reconsideration or reinvestigation within 30 days from receipt. Missing this deadline generally makes the assessment final, executory, and demandable.
Request for reinvestigation: submit all relevant supporting documents within 60 days from filing the protest.
Denial or Final Decision on Disputed Assessment (FDDA): appeal to the Court of Tax Appeals (CTA), or take an available administrative appeal, within the applicable 30-day period.
BIR inaction: after the applicable 180-day decision period, either appeal the inaction to the CTA within 30 days or wait for the BIR’s final decision. Those choices are mutually exclusive.

These periods are strict. Record the exact date and manner of receipt, obtain proof of every filing, and do not rely on an informal conversation, an unanswered email, or a request for more time.

The critical deadlines

Event	Required action	Deadline
Receipt of PAN	Submit a substantive written reply	15 days from receipt
Receipt of FLD/FAN	File a request for reconsideration or reinvestigation	30 days from receipt
Filing a request for reinvestigation	Submit all relevant supporting documents	60 days from filing
Reconsideration pending before the authorized BIR representative	Track BIR decision period	180 days from filing the protest
Reinvestigation pending before the authorized BIR representative	Track BIR decision period	180 days from submission of the supporting documents
Denial by an authorized BIR representative	Appeal to the CTA or elevate the matter to the Commissioner, as applicable	30 days from receipt
Denial by the Commissioner	Appeal to the CTA	30 days from receipt
Inaction after the applicable 180-day period	Appeal the inaction to the CTA, or wait for a final decision	CTA appeal must be filed within 30 days after the 180-day period if that option is chosen

The governing procedure appears in Section 228 of the National Internal Revenue Code and Revenue Regulations No. 18-2013.

Count from the date of legally effective receipt, not simply the date printed on the document. Because computation can be affected by the manner of service, a weekend or holiday, or a special government deadline suspension, calculate conservatively and file early.

First identify what the BIR sent

Notice of Discrepancy or audit communication

A Notice of Discrepancy, request for records, or invitation to a discussion is generally part of the audit process. It should be answered seriously because factual errors may be corrected before an assessment is issued. However, it is not normally the FLD/FAN that triggers the 30-day protest under Section 228.

Preserve the Letter of Authority or electronic Letter of Authority covering the audit. The assigned revenue officers, taxable period, tax types, and scope should be reviewed. In 2026, the BIR introduced an official LOA Verifier through Chatbot REVIE. Verification does not replace a legal review of the officers’ authority or the audit’s scope.

Preliminary Assessment Notice

A PAN states the proposed deficiencies and their bases. Under Revenue Regulations No. 18-2013, the taxpayer has 15 days from receipt to respond.

Use the reply to:

dispute incorrect facts and computations;
reconcile tax returns, books, invoices, withholding certificates, and third-party information;
identify payments, credits, or carryovers the BIR overlooked;
challenge unsupported assumptions or legal interpretations;
raise procedural objections; and
submit documents that may prevent the proposed adjustment from reaching the final-assessment stage.

Failure to reply allows the BIR to proceed with an FLD/FAN, but the assessment must still be protested after the FLD/FAN is received. A reply to the PAN normally does not substitute for the 30-day protest against the FLD/FAN.

A PAN is not required in the limited situations specified by Section 228, including certain mathematical errors apparent on the return, discrepancies between tax withheld and remitted, improper use of an amount also claimed as a refund or tax credit, unpaid excise tax, and transfers of specified tax-exempt purchases to non-exempt persons. In those cases, the BIR may issue the FLD/FAN directly.

Formal Letter of Demand and Final Assessment Notice

The FLD/FAN is the document that ordinarily triggers the 30-day administrative-protest period. Treat any document demanding payment and presenting itself as a final assessment as urgent, even if its label or attachments appear irregular.

The assessment should inform the taxpayer in writing of the facts and law on which it is based. An assessment that fails this requirement may be void, but whether the defect is fatal depends on the complete notices, schedules, attachments, and circumstances. The Supreme Court discusses this due-process requirement in Commissioner of Internal Revenue v. Liquigaz Philippines Corporation.

Choose the correct kind of protest

Request for reconsideration

A request for reconsideration asks the BIR to reevaluate the assessment using the records already available, without newly discovered or additional evidence. It may raise factual questions, legal questions, or both.

This route may fit when:

the BIR made a mathematical or legal error apparent from the existing record;
the necessary returns, ledgers, schedules, and submissions are already in the audit docket; or
the dispute turns primarily on statutory interpretation.

The special 60-day supporting-document period does not apply to a reconsideration. The BIR’s 180-day period is generally counted from the filing of the protest.

Do not select reconsideration merely because it appears simpler if the defense actually requires documents not already in the record.

Request for reinvestigation

A request for reinvestigation asks for reevaluation based on newly discovered or additional evidence. The protest must identify the evidence the taxpayer intends to submit.

All relevant supporting documents must be submitted within 60 days from filing the protest. The BIR’s 180-day period is generally counted from the date those documents are submitted within the 60-day window.

This route may fit when the taxpayer needs to provide additional:

invoices, official receipts, or other transaction records;
bank records or proof of remittance;
withholding-tax certificates;
contracts and supporting correspondence;
inventory, payroll, or expense schedules;
accounting reconciliations;
proof of tax credits or prior payments; or
affidavits and records explaining transactions questioned during the audit.

The taxpayer determines which documents are relevant to the factual and legal grounds raised. Submit a complete, indexed package and identify what each document proves. Failure to meet the 60-day requirement can prevent the taxpayer from using new or additional evidence to dispute the assessment.

What a valid protest should contain

A bare statement such as “we disagree,” “please reconsider,” or “the assessment is excessive” is dangerous. Revenue Regulations No. 18-2013 require a protest with specified information and support.

Quick answer

To challenge a BIR deficiency-tax assessment, act according to the notice you received:

Preliminary Assessment Notice (PAN): submit a written response within 15 days from receipt.
Formal Letter of Demand and Final Assessment Notice (FLD/FAN): file a valid written administrative protest—either a request for reconsideration or request for reinvestigation—within 30 days from receipt.
Request for reinvestigation: submit all relevant supporting documents within 60 days from filing the protest.
Denial or Final Decision on Disputed Assessment (FDDA): appeal to the Court of Tax Appeals (CTA), or where permitted elevate the protest to the Commissioner of Internal Revenue, within 30 days from receipt.
BIR inaction: after the applicable 180-day decision period, either appeal the inaction to the CTA within the next 30 days or wait for the BIR’s final decision and appeal that decision within 30 days after receiving it.

These periods are critical. An incomplete, late, or improperly filed protest can make the assessment final, executory, and demandable. Start counting from the actual or legally effective date of receipt, preserve proof of that date, and file early.

The deadlines at a glance

Stage	What to do	General deadline
Notice of Discrepancy or audit findings	Attend the discussion and submit explanations requested in the notice	Follow the notice and applicable BIR issuance
PAN	File a substantive written response	15 days from receipt
FLD/FAN	File a request for reconsideration or reinvestigation	30 days from receipt
Reinvestigation	Submit all relevant supporting documents	60 days from filing the protest
Inaction on reconsideration	Count the BIR’s action period from filing of the protest	180 days
Inaction on reinvestigation	Count the BIR’s action period from submission of the supporting documents	180 days
Denial by an authorized representative	Appeal to the CTA or elevate to the Commissioner, as applicable	30 days from receipt
Denial by the Commissioner	Appeal to the CTA	30 days from receipt
CTA appeal based on inaction	File after the 180-day period expires	Within the next 30 days

The governing procedure is principally found in Section 228 of the National Internal Revenue Code and Revenue Regulations No. 18-2013, which amended RR No. 12-99.

First identify what you received

Not every BIR letter is the assessment that must be protested within 30 days.

Notice of Discrepancy

A Notice of Discrepancy ordinarily gives the taxpayer an opportunity to discuss audit findings before the assessment stages. Use it to correct factual errors, reconcile third-party information, and narrow the disputed issues. Comply with the deadline stated in the notice, but continue monitoring for a PAN or FLD/FAN.

Preliminary Assessment Notice

A PAN states the BIR’s proposed deficiency findings. It should explain the facts and legal bases for those findings. A response to the PAN is important, but it is not the administrative protest contemplated by the 30-day rule.

File a detailed response within 15 days from receipt. Address every disputed finding and attach the records already available. If no timely response is made, the BIR may issue an FLD/FAN.

A PAN is not required in the specific cases listed in Section 228, including certain mathematical errors apparent from the return, discrepancies between tax withheld and tax remitted, specified refund-and-carryover situations, unpaid excise tax, and transfers of exemptly acquired articles to non-exempt persons. In those cases, the BIR may issue the FLD/FAN directly.

Formal Letter of Demand and Final Assessment Notice

The FLD/FAN is the formal assessment and demand for payment. This is the document that must generally be protested within 30 days from receipt.

Do not assume that a detailed PAN response protects you from the FAN deadline. Even if the FLD/FAN repeats the PAN, file a separate, timely administrative protest against the FLD/FAN.

Final Decision on Disputed Assessment

An FDDA disposes of the protest in whole or in part. It should state the facts and legal bases for the decision and make clear that it is the BIR’s final decision. A denial may also appear in another communication whose substance shows that the BIR has finally rejected the protest and demanded payment. Have any collection or demand letter reviewed immediately rather than relying only on its title.

Step 1: Lock down the receipt date

The countdown normally turns on receipt, not merely the date printed on the notice. Preserve:

The complete notice and all attachments.
The envelope, registry notice, courier pouch, waybill, and tracking record.
The date, time, place, and manner of personal delivery.
The name and position of the person who accepted the notice.
Any BIR acknowledgment or service report available to you.
The authority of a tax agent or representative who received it.
Evidence of the taxpayer’s registered address at the time of service.

Under RR No. 18-2013, notices may be served personally, by authorized substituted service, or by mail or professional courier. Service on an appointed tax agent in the circumstances covered by the regulations may be treated as service on the taxpayer. Refusing delivery is not a safe strategy because substituted-service procedures may still apply.

Improper service can be material, but it is evidence-dependent. In CIR v. South Entertainment Gallery, Inc., the Supreme Court examined whether the BIR had proved proper service of the assessment at the taxpayer’s registered address. Raise a service objection expressly and preserve it; do not simply ignore a notice that has actually reached you.

Step 2: Audit the assessment issue by issue

Prepare a schedule matching every assessed item with the BIR’s computation, your position, and your supporting proof. Check at least the following:

Correct taxpayer, TIN, taxable period, and tax type.
Amount of basic tax, surcharge, interest, and other additions.
Returns, payments, tax credits, withholding certificates, and prior adjustments.
Reconciliations between books, returns, audited financial statements, and third-party data.
Whether the BIR used unsupported assumptions, estimates, or duplicated transactions.
Whether exemptions, deductions, zero-rating, withholding credits, or timing differences were treated correctly.
Whether the assessment was issued within the applicable prescriptive period, taking account of the filing date, alleged fraud or non-filing, and any waiver.
Whether the audit was conducted by revenue officers with a valid Letter of Authority covering the correct taxpayer, period, and taxes.
Whether the PAN, FLD/FAN, and FDDA adequately state the factual and legal bases required by law.
Whether the notices were issued, signed, and served by officials with the required authority.

The ordinary assessment period is generally three years, subject to statutory exceptions such as a false or fraudulent return with intent to evade tax or failure to file a return. Prescription calculations can be altered by the type and filing date of the return, valid waivers, and other facts, so do not rely on a simple anniversary calculation.

Authority defects can also be decisive. The Supreme Court has held that an audit by a replacement revenue officer without the required authority may invalidate the resulting assessment. See CIR v. McDonald’s Philippines Realty Corp.. As of 2026, taxpayers may also verify an LOA using the BIR’s Chatbot REVIE feature described in RMC No. 5-2026.

These possible defects should be raised in the protest, but none should be asserted without reviewing the actual documents and controlling law.

Step 3: Choose the correct kind of protest

Request for reconsideration

Choose reconsideration when you want the BIR to re-evaluate the assessment using the records already available, without newly discovered or additional evidence. It may raise factual questions, legal questions, or both.

For a reconsideration, the 180-day action period generally begins on the date the protest is filed. The separate 60-day document-submission period does not apply.

This option can be suitable when the dispute is mainly legal or when the complete evidentiary record is already before the BIR. It can be risky if important documents have not yet been submitted.

Request for reinvestigation

Choose reinvestigation when you will present newly discovered or additional evidence. The protest must identify the additional evidence you intend to submit.

All relevant supporting documents must be submitted within 60 days from filing the protest. The 180-day action period generally begins when those documents are submitted within that period.

Use reinvestigation only if you can organize and submit the needed evidence on time. Failure to complete the submission can prevent you from introducing the additional evidence and lead to denial of the protest.

Step 4: Make the protest valid and complete

A bare statement such as “we disagree with the assessment” is not enough. The protest should ordinarily contain:

The taxpayer’s complete name, TIN, registered address, and contact details.
The date and identifying numbers of the FLD/FAN.
The date and manner in which the FLD/FAN was received.
A clear statement that the filing is an administrative protest under Section 228.
The chosen nature of the protest: reconsideration or reinvestigation.
The tax types, taxable periods, amounts, and issues being disputed.
A separate statement of facts for each issue.
The statutes, regulations, jurisprudence, and BIR issuances supporting each objection.
The computations and documentary evidence supporting the taxpayer’s position.
For reinvestigation, a description of the additional evidence to be presented.
The precise relief requested, such as cancellation, withdrawal, or reduction of specified assessments.
Identification of any undisputed issues and the corresponding payment arrangements.
The taxpayer’s or duly authorized representative’s signature and proof of authority.

Address every issue. Under RR No. 18-2013, an issue not supported by its facts and legal basis may be treated as undisputed. If only part of the assessment is contested, the portion attributable to undisputed issues may become final and collectible.

Step 5: File with the proper BIR office and prove timely filing

BIR guidance directs taxpayers to file the PAN response and the FLD/FAN protest with the duly authorized representative who signed the notices. An administrative appeal elevated to the Commissioner is filed with the Office of the Commissioner. See RMC No. 11-2014.

Check the notice for the responsible office and current filing instructions. Do not assume that sending a copy to the revenue officer, discussing the matter at a conference, or emailing an employee constitutes formal filing.

Obtain reliable proof, such as:

A receiving copy stamped with the date, time, office, and receiving officer.
An official electronic acknowledgment if the BIR has expressly authorized that filing channel.
A registry receipt, proof of delivery, and complete copy of the mailed submission if an authorized mailing method is used.
An index showing every annex submitted.
Proof of the signer’s authority, such as an appropriate special power of attorney or corporate authorization.

Keep identical electronic and physical copies. If an annex is later questioned, the receiving copy and index can show exactly what was submitted.

Step 6: Complete the evidence within the allowed period

For a reinvestigation, do not wait for the BIR to tell you which evidence is “relevant.” RR No. 18-2013 describes relevant supporting documents as those necessary to support the legal and factual bases of the taxpayer’s dispute, as determined by the taxpayer.

Depending on the issues, preserve and submit properly organized copies of:

Tax returns, amended returns, and proof of filing.
Payment confirmations and BIR Form 0605 records, if applicable.
Certificates of creditable or final tax withheld.
Books of accounts, ledgers, journals, and trial balances.
Audited financial statements and working papers.
Sales invoices, official receipts for periods when applicable, billing records, and contracts.
Purchase documents, import records, and proofs of payment.
Bank statements and transaction reconciliations.
Payroll, withholding, and remittance records.
Board resolutions, corporate records, and authority documents.
Relevant correspondence with the BIR.
The LOA or eLA, notices, waivers, and proof of their service or execution.
Expert computations or affidavits when genuinely necessary.

Explain what each document proves. A large, unindexed document dump is harder to evaluate and may fail to connect the evidence to the disputed findings.

What happens after the protest

Denial by the Commissioner’s authorized representative

If the protest is denied wholly or partly by an authorized representative, the taxpayer generally has two alternatives within 30 days from receipt:

File a petition for review with the CTA; or
Elevate the protest to the Commissioner through a request for reconsideration.

An administrative appeal to the Commissioner cannot be a new reinvestigation. Under RR No. 18-2013, only issues raised in the authorized representative’s decision will be entertained at that stage.

Denial by the Commissioner

If the Commissioner denies the protest or administrative appeal, file a petition for review with the CTA within 30 days from receipt. A further motion for reconsideration addressed to the Commissioner does not stop or extend the CTA appeal period.

A CTA petition is a judicial pleading, not another protest letter. It must comply with the Revised Rules of the Court of Tax Appeals, including requirements on jurisdictional allegations, verification, certification against forum shopping, attachments, and docket fees. Engage Philippine tax counsel well before the deadline.

BIR inaction for 180 days

If the BIR does not act within the applicable 180-day period, the taxpayer may:

Appeal the inaction to the CTA within 30 days after the 180-day period expires; or
Wait for the BIR’s final decision and appeal that decision within 30 days from receipt.

These options are mutually exclusive once one is chosen. The Supreme Court confirmed them in Lascona Land Co., Inc. v. CIR.

Calculate the 180-day period carefully. For reconsideration, it generally runs from filing of the protest. For reinvestigation, it generally runs from timely submission of the relevant supporting documents. Record the exact date of submission and the documents included.

A 2026 issue: consolidated assessment notices

Under the BIR’s current single-instance audit framework, certain pending audits and assessments may be consolidated. RMO No. 6-2026 prescribes safeguards for consolidation at the FAN stage.

Where a Consolidated FAN is validly issued under that order, it must expressly supersede the earlier FAN for consolidation purposes and be properly served; a fresh 30-day protest period runs from receipt of the Consolidated FAN. Consolidation may also involve written conformity and a waiver of prescription.

If you receive a Consolidated PAN or FAN:

Preserve both the original and consolidated notices.
Check which notices and taxable periods were consolidated.
Verify whether the required safeguards and service rules were followed.
Do not assume the earlier protest automatically covers the consolidated notice.
File a protective, issue-specific response or protest within the new stated period after obtaining advice.
Review any requested waiver before signing it because a waiver may materially affect prescription defenses.

Does protesting stop collection?

A valid and timely protest prevents the disputed portions from becoming final merely because the initial 30-day period expired. It does not mean that interest exposure disappears.

Once the dispute reaches the CTA, an appeal does not automatically suspend payment, levy, distraint, or sale of property. Section 11 of Republic Act No. 1125, as amended by RA No. 9282, allows the CTA to suspend collection when collection may jeopardize the interests of the government or taxpayer, generally subject to a deposit or surety bond of not more than twice the amount claimed. The application of the bond requirement and recognized exceptions depends on the circumstances and court rulings.

Seek urgent help if the BIR issues or threatens a warrant of distraint or levy, bank garnishment, tax lien, seizure notice, or court collection action.

Common mistakes that can forfeit the protest

Treating a PAN response as the protest against the FLD/FAN.
Counting from the date of the notice instead of investigating the legally effective receipt date.
Waiting until the last day and encountering a filing or delivery problem.
Asking for an extension without legal authority and assuming the request stops the deadline.
Filing with the revenue officer instead of the proper signatory office.
Sending an informal email without an authorized filing acknowledgment.
Failing to identify the filing as reconsideration or reinvestigation.
Choosing reconsideration despite needing evidence not already in the record.
Missing the 60-day document deadline for reinvestigation.
Failing to address every assessed issue separately.
Ignoring the undisputed part of an assessment.
Submitting evidence without explaining which issue it proves.
Filing a motion for reconsideration with the Commissioner and mistakenly believing it tolls the CTA deadline.
Waiting past the 30-day CTA period after receiving an FDDA.
Ignoring a demand or collection letter because it is not labelled “FDDA.”
Signing a waiver of prescription or written conformity to consolidation without reviewing its effect.
Failing to update the taxpayer’s registered address and monitor mail received by staff or tax agents.

When professional help is urgent

Contact a Philippine tax lawyer immediately if:

Fewer than ten days remain before a PAN, FLD/FAN, FDDA, or CTA deadline.
The assessed amount is material to the taxpayer’s operations or personal assets.
Fraud, false returns, fake transactions, or criminal tax charges are alleged.
A warrant, garnishment, levy, lien, seizure notice, or collection case has been issued.
Service was made at an old or disputed address.
The audit appears to lack a valid LOA or was conducted by officers not named in it.
The assessment may have prescribed.
You received inconsistent, supplemental, or consolidated assessment notices.
A waiver of prescription is requested.
The BIR has been inactive for nearly 180 days and you must choose whether to appeal the inaction.
An FDDA or equivalent final denial has been received.

A CPA can reconstruct records and computations, but legal issues concerning validity, jurisdiction, prescription, service, collection remedies, and CTA litigation should be coordinated with qualified Philippine tax counsel.

Frequently asked questions

Can I protest a PAN within 30 days?

The regulatory response period for a PAN is 15 days from receipt. The 30-day administrative-protest period applies to the FLD/FAN.

Can I ask the BIR for more time to protest a FAN?

Do not rely on an extension. The 30-day protest period is treated as mandatory, and a late protest ordinarily leaves the assessment final, executory, and demandable.

Is a reconsideration safer than a reinvestigation?

Not automatically. Reconsideration avoids the separate 60-day document deadline but is limited to the existing record. Reinvestigation permits additional evidence but requires complete, timely submission. Choose based on what the case actually needs.

Must I pay the whole assessment before protesting?

A timely administrative protest may dispute all or part of the FLD/FAN. Amounts attributable to issues not disputed with proper factual and legal support can become final and collectible. Payment, refund, and recovery strategies have separate consequences and should be evaluated before paying.

What if the BIR never answers?

After the applicable 180-day period, you may appeal the inaction to the CTA within the following 30 days or wait for a final BIR decision. Calendar both routes before choosing.

Can I go directly to a regular court?

Generally, disputes over BIR assessments and related matters fall within the exclusive jurisdictional framework of the CTA after the required administrative steps. Filing in the wrong court does not protect the deadline.

Does an invalid assessment still need to be protested?

Raise the invalidity in a timely protest whenever possible. A taxpayer should not assume that an alleged defect permits ignoring the FLD/FAN. Whether a defect makes an assessment void is often document- and fact-specific.

Official sources

This article provides general legal information, not legal, tax, or accounting advice for a particular assessment. Deadlines and remedies can turn on the exact notice, service record, audit history, documents, and later government issuances. Sources were checked as of August 3, 2026.