Quick answer

To challenge a BIR deficiency tax assessment, file a valid written administrative protest against the Formal Letter of Demand and Final Assessment Notice (FLD/FAN) within 30 days from receipt. Choose either:

Reconsideration — the BIR re-evaluates the assessment using records already submitted; or
Reinvestigation — you will present newly discovered or additional evidence. Submit all relevant supporting documents within 60 days from filing the protest.

Address every disputed issue separately, with its supporting facts and legal basis. A vague objection, a late protest, or failure to support an issue may allow the corresponding assessment to become final, executory, and demandable.

If the protest is denied, or the BIR does not act within the applicable 180-day period, the next remedy may be an appeal to the Court of Tax Appeals (CTA). The CTA deadline is generally 30 days and must be treated as strict.

First identify the document you received

Not every BIR notice starts the 30-day protest period.

Document	What it generally means	Immediate action
Letter of Authority or electronic LOA	Authority for named revenue officers to conduct an examination	Verify the authority, officers, taxable period, and covered taxes; organize records
Notice of Discrepancy	Audit findings requiring discussion or explanation	Attend or respond within the period stated in the notice
Preliminary Assessment Notice (PAN)	Proposed deficiency assessment	Submit a written response within 15 days from receipt, unless the case is one where a PAN is not required
FLD/FAN	Formal assessment and demand for payment	File a valid administrative protest within 30 days from receipt
Final Decision on Disputed Assessment (FDDA)	Decision on a protest	Determine immediately whether to appeal to the Commissioner or the CTA; a 30-day period usually applies
Collection letter, Final Notice Before Seizure, warrant of distraint or levy, or garnishment notice	The BIR is pursuing collection	Obtain urgent tax-litigation advice; do not assume an earlier protest or CTA appeal automatically stops collection

A response to a PAN is not the same as the administrative protest required after an FLD/FAN. Even if you fully answered the PAN, you must file a new and timely protest when the FLD/FAN arrives. The Supreme Court has emphasized that it is the FLD/FAN—not the PAN—that must be administratively protested within 30 days.

A PAN is generally required, but Section 228 of the Tax Code permits an FLD/FAN to be issued without one in specified cases, including certain mathematical errors apparent on the return, discrepancies between tax withheld and remitted, double use of excess creditable withholding tax, unpaid excise tax, and transfers of tax-exempt articles to non-exempt persons.

The essential deadlines

Event	Deadline or period
Response to PAN	Within 15 days from receipt
Protest against FLD/FAN	Within 30 days from receipt
Supporting documents for reinvestigation	Within 60 days from filing the protest
BIR period to act on reconsideration	180 days from filing the protest
BIR period to act on reinvestigation	180 days from submission of the required supporting documents within the 60-day period
Appeal from an adverse decision of an authorized BIR representative	Within 30 days from receipt, either to the CTA or, where permitted, to the Commissioner
Appeal from the Commissioner’s adverse decision	Petition for review with the CTA within 30 days from receipt
Appeal based on BIR inaction	Petition for review with the CTA within 30 days after the applicable 180-day period expires, or await a final decision and appeal that decision within 30 days from receipt

Record the actual date and manner of receipt. Preserve the envelope, registry notice, courier record, receiving log, email, and any acknowledgment signed by an employee or representative. Service on an appointed tax agent may be treated as service on the taxpayer. Notices may also be served at a taxpayer’s registered or known address under the applicable BIR regulations, so an outdated BIR registration can create serious problems.

Count conservatively and do not assume that discussions with examiners, requests for records, settlement talks, or informal assurances extend a statutory deadline.

Choose reconsideration or reinvestigation deliberately

Request for reconsideration

Use reconsideration when the assessment can be challenged using the records already available to the BIR. Typical issues may include:

An incorrect interpretation of the Tax Code or regulations;
A mathematical or classification error;
Double counting of income or transactions;
Failure to credit payments or withholding taxes already shown in existing records;
An assessment issued outside the applicable prescriptive period;
Lack of authority of the revenue officers who conducted the examination; or
Failure of the FLD/FAN to state an adequate factual and legal basis.

The 60-day supporting-document period does not apply to a request for reconsideration because the remedy is based on existing records. The 180-day period for BIR action is counted from filing of the protest.

Request for reinvestigation

Use reinvestigation when you need the BIR to consider newly discovered or additional evidence. The protest must identify the additional evidence you intend to present. All relevant supporting documents must then be submitted within 60 days from filing the protest.

The Supreme Court has confirmed that this 60-day period concerns a reinvestigation requested in the protest against the FLD/FAN—not the taxpayer’s earlier response to the PAN. See the Supreme Court’s decision in CIR v. Maxicare Healthcare Corporation.

For a reinvestigation, remove uncertainty about the start of the 180-day period. Submit an indexed package, obtain proof of receipt, and state in writing when the submission is complete and no further supporting documents will be presented.

Do not label a protest one way while using it as the other. If additional evidence is necessary, a nominal “reconsideration” may leave that evidence outside the remedy selected. Conversely, a reinvestigation creates a strict 60-day document deadline.

What a valid protest should contain

A defensible protest is more than a letter saying that the taxpayer disagrees. It should include:

Taxpayer identification. State the taxpayer’s registered name, TIN, address, contact details, taxable year or period, and the relevant BIR office.
Assessment identification. State the date and reference numbers of the FLD/FAN and assessment notices, the tax types involved, and the date and manner of receipt.
The chosen remedy. Expressly state whether the protest is a request for reconsideration or reinvestigation. For reinvestigation, identify the newly discovered or additional evidence to be presented.
Scope of the protest. State whether the entire assessment or only specified portions are disputed. Identify each tax type, taxable period, issue, and amount involved.
Issue-by-issue facts. Explain what occurred, what the BIR found, why the finding is incorrect, and what the correct treatment should be.
Legal basis for each issue. Cite the applicable statutory provision, regulation, controlling jurisprudence, treaty provision, or other relevant authority. Revenue Regulations No. 18-2013 requires the applicable legal basis to be stated; merely attaching the assessment is not enough.
Supporting computation. Provide a reconciliation from the BIR’s figure to the taxpayer’s proposed figure. Separate basic tax, surcharge, interest, and other additions.
Evidence. Attach an indexed set of relevant records or, for a reinvestigation, identify what will follow within the 60-day period.
Relief requested. Ask for cancellation or appropriate reduction of the disputed assessment and issuance of the proper final decision or authority reflecting the result.
Authority of the signatory. Include the appropriate special power of attorney, board resolution, secretary’s certificate, or other proof of authority when a representative signs or files for the taxpayer.

Revenue Regulations No. 18-2013 treats unaddressed issues as undisputed. If an FLD/FAN contains several findings, a general discussion of only one finding will not necessarily preserve objections to the others. State facts and legal grounds for every issue you intend to contest.

Where and how to file

BIR guidance directs the taxpayer to file the protest with the duly authorized representative of the Commissioner who signed the FLD/FAN. An administrative appeal to the Commissioner, when available, is filed with the Office of the Commissioner. See BIR Revenue Memorandum Circular No. 11-2014.

Follow the filing instructions in the assessment and confirm the receiving office before the deadline. Because procedures and office assignments can change:

Obtain a stamped “received” copy showing the date, time, office, and receiving officer;
If an officially accepted mailing or delivery method is used, retain the receipt, tracking history, proof of delivery, and a complete copy of what was sent;
Keep a contemporaneous filing memo identifying every enclosure;
Do not rely only on an examiner’s acknowledgment through a call, text message, or informal email; and
Do not assume that submission to the wrong office, or to an individual revenue officer instead of the proper receiving office, preserves the deadline.

Review the assessment for procedural and substantive defenses

A protest should challenge both the amount assessed and any defects affecting the assessment’s validity.

Authority to examine

Check the LOA or eLA, the taxable period and taxes it covers, the officials who issued it, and the revenue officers named in it. The Supreme Court has held that the revenue officer conducting the examination must have the required authority and that an internal reassignment document does not automatically substitute for a new or amended LOA. See CIR v. McDonald’s Philippines Realty Corporation.

A Letter Notice, Mission Order, or other limited verification instrument should not simply be assumed to confer the same authority as an LOA. The effect depends on the document, the work actually performed, and the governing issuance.

Proper notice and service

Determine whether the PAN, FLD/FAN, and FDDA were served in the manner required by the regulations. Identify who received each document and whether that person was authorized. Non-receipt and defective service are fact-intensive issues, so preserve building logs, personnel records, courier documents, registered-mail records, and affidavits from people with direct knowledge.

Adequate factual and legal basis

Section 228 requires the taxpayer to be informed in writing of the law and facts on which the assessment is made; otherwise, the assessment is void. Revenue Regulations No. 18-2013 likewise requires the FLD/FAN to state its factual and legal bases.

An FDDA must state the facts and applicable law, regulations, or jurisprudence on which the decision rests and must identify itself as the final decision. However, a defective FDDA does not automatically invalidate an otherwise valid underlying assessment. The assessment and the decision on the protest are legally distinct, as explained in CIR v. Liquigaz Philippines Corporation.

Prescription

Internal revenue taxes generally must be assessed within three years after the last day prescribed for filing the return, or from actual filing when the return was filed late. Different rules may apply when no return was filed, or when the BIR alleges a false or fraudulent return with intent to evade tax. A valid written waiver may also affect the period.

Prescription analysis depends on the return, filing date, assessment date, service, waivers, and any applicable exception. Preserve every return, electronic filing confirmation, waiver, acceptance document, and assessment envelope.

Correctness of the assessment

Test the BIR’s schedules against original records. Common factual disputes involve:

Third-party information attributed to the wrong taxpayer or period;
Timing differences mistaken for undeclared income;
Duplicate sales or purchases;
Unsupported assumptions about bank deposits;
Disallowed expenses for which documents exist;
Input VAT, withholding-tax credits, or prior payments not recognized;
Incorrect tax rates or taxable bases;
Transactions covered by exemptions, incentives, or treaties;
Amounts already subjected to another tax treatment; and
Incorrect surcharge or interest computations.

The taxpayer usually needs competent evidence, not only explanations. Reconstructing records after the 60-day reinvestigation period has expired may be too late.

What happens after the protest

If an authorized representative denies the protest

When the denial or FDDA is issued by the Commissioner’s duly authorized representative, the taxpayer may generally choose, within 30 days from receipt, either to:

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

The administrative appeal to the Commissioner is limited to reconsideration. A new reinvestigation is not available at that stage, and only issues raised in the authorized representative’s decision will be entertained under Revenue Regulations No. 18-2013.

If the Commissioner denies the protest or administrative appeal

File a petition for review with the CTA within 30 days from receipt. A motion asking the Commissioner to reconsider the denial does not suspend or restart the 30-day CTA period.

The petition goes to a CTA Division. The CTA rules require the prescribed petition, attachments, copies, and payment of docket and lawful fees. A defective or late judicial filing may be dismissed regardless of the merits, so engage counsel before the period is close to expiring.

There is no minimum assessment amount that must be reached before a taxpayer can appeal a disputed BIR assessment to the CTA. The monetary thresholds in the CTA law for certain original criminal and collection cases are different jurisdictional rules.

If the BIR does not act within 180 days

The taxpayer has two mutually exclusive options:

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

Failure to appeal immediately after 180 days does not, by itself, eliminate the option to await the final decision. This rule is established in Lascona Land Co., Inc. v. CIR and reaffirmed in Mannasoft Technology Corporation v. CIR.

The choices are mutually exclusive. Once the taxpayer files a CTA case based on inaction, a later BIR decision does not create a new administrative route. If the taxpayer waits, the date the eventual decision is received becomes critical.

The lapse of 180 days is not an automatic victory on the merits. It is treated as inaction or a deemed denial for purposes of allowing a CTA appeal.

A CTA appeal does not automatically stop collection

Under Republic Act No. 1125, as amended by Republic Act No. 9282, an appeal to the CTA generally does not suspend payment, levy, distraint, or sale of property. The CTA may suspend collection when collection may jeopardize the interests of the Government or the taxpayer, subject to the governing requirements. A verified motion for suspension may be filed with the petition or later in the case.

If a warrant, garnishment, levy, or sale is threatened, counsel may need to seek immediate CTA relief. The timing, supporting evidence, and possible deposit or surety-bond requirement must be evaluated promptly. See the CTA’s Revised Rules, particularly Rule 10.

Collection while a timely and valid administrative protest is still unresolved may raise separate issues. In Mannasoft, the Supreme Court explained that summary collection remedies require delinquent taxes and found that premise absent while the taxpayer’s valid reinvestigation request remained pending. Whether that reasoning applies to a particular collection notice depends on the record and procedural posture.

Evidence to preserve

Create a secure electronic and paper case file containing:

LOA or eLA, Mission Order, Notice of Discrepancy, PAN, FLD/FAN, FDDA, and every collection notice;
Original envelopes, registry cards, courier receipts, tracking reports, and receiving logs;
Tax returns, filing confirmations, payment records, and withholding certificates;
Books, ledgers, invoices, receipts, contracts, bank records, and reconciliations;
BIR audit schedules and working papers provided to the taxpayer;
Every submission to the BIR, with its annexes and proof of receipt;
Meeting notices, minutes, correspondence, and names of participants;
Waivers of the statute of limitations and related acceptance documents;
The LOA’s named officers and records showing who actually conducted the audit;
Corporate authorizations or powers of attorney;
Proof of changes in address or registration; and
Native electronic files, metadata, and reliable backups.

Do not alter original records. If an explanation requires a revised schedule, retain the original and label the revision clearly.

Common mistakes that can defeat a protest

Treating a PAN response as the protest against the FLD/FAN;
Counting from the date printed on the notice instead of carefully establishing the date of receipt;
Filing after the 30-day period;
Failing to say whether the request is for reconsideration or reinvestigation;
Requesting reinvestigation but missing the 60-day document deadline;
Making a blanket objection without facts and legal authority for each issue;
Ignoring one tax type or assessment item in a multi-issue FLD/FAN;
Filing with the wrong office or keeping no proof of filing;
Assuming informal conferences or settlement negotiations stop the clock;
Asking the Commissioner to reconsider an adverse decision and assuming that request tolls the CTA deadline;
Appealing directly to the CTA before filing the required administrative protest;
Losing track of the 180-day period and the chosen remedy for inaction;
Assuming a CTA petition automatically suspends collection; and
Failing to update the registered address or monitor notices received by employees and tax agents.

When professional help is urgent

Seek a Philippine tax lawyer or experienced tax-litigation team immediately if:

An FLD/FAN was received and the 30-day period is already running;
The reinvestigation document deadline is approaching;
An FDDA or other apparent final denial has arrived;
The BIR has issued a warrant of distraint or levy, bank garnishment, Final Notice Before Seizure, or notice of sale;
The assessment alleges fraud, substantial underdeclaration, or a false return;
A subpoena, criminal referral, or tax-evasion complaint is involved;
The assessment concerns withholding taxes, multiple taxable years, or a large exposure;
The audit may have been conducted without a valid LOA or by unauthorized officers;
Service, prescription, or the validity of a waiver is disputed; or
The taxpayer is considering an appeal based on 180-day inaction.

Frequently asked questions

Can I protest an assessment by simply writing “I disagree”?

No. The protest must meet the form and content required by Revenue Regulations No. 18-2013. It should identify the nature of the protest, the assessment date, and the applicable legal authorities, and it must give facts and legal grounds for each disputed issue.

Do I have to pay before filing an administrative protest?

Section 228 does not generally require full payment as a condition for protesting an FLD/FAN. If only part of the assessment is disputed, the undisputed portion may become final and should be addressed separately. Payment can also affect available remedies, so obtain advice before paying a disputed amount in full.

Can the 30-day protest period be extended?

Do not assume so. The Tax Code states that the protest must be filed within 30 days from receipt, and the regulations provide that failure to file a valid protest within that period makes the assessment final, executory, and demandable.

What if the taxpayer never received the FLD/FAN?

Valid service and actual receipt are factual questions. Check the registered address, mail and courier records, employee authority, and whether service was made on an appointed tax agent. Non-receipt may be a substantial defense, but it should be supported by evidence and raised promptly.

What if the 30-day protest deadline was missed?

As a general rule, the assessment becomes final, executory, and demandable, and the BIR will not grant reconsideration or reinvestigation of an assessment that has already become final. Possible issues concerning void assessment, lack of authority, prescription, or defective service require urgent case-specific analysis and should not be treated as a routine excuse for late filing.

Does BIR inaction after 180 days mean the assessment is cancelled?

No. Inaction permits a CTA appeal but does not decide the merits in the taxpayer’s favor. The taxpayer may appeal within the 30-day window after the 180-day period or await the final BIR decision and then appeal within 30 days from receipt.

Can a protest be filed electronically?

The controlling guidance directs filing with the duly authorized representative who signed the FLD/FAN. Follow the assessment’s instructions and confirm the currently accepted filing method with the proper BIR office. Do not rely on an email transmission unless that method is officially accepted for the particular filing and you obtain verifiable proof of timely receipt.

Does the amount of the assessment change the protest deadlines?

No. The Section 228 deadlines apply regardless of the assessment’s size. Separate monetary thresholds govern jurisdiction over certain criminal and collection cases, not the basic administrative protest deadline for a disputed assessment.

Official legal sources

This article provides general legal information, not legal or tax advice, and does not create an attorney-client relationship. The correct remedy may depend on the assessment documents, dates of receipt, tax period, evidence, and procedural history. Sources and procedures were checked as of August 3, 2026.