Quick answer

To contest a Bureau of Internal Revenue assessment, file a valid written protest against the Formal Letter of Demand and Final Assessment Notice (FLD/FAN) within 30 calendar days from receipt. State whether you seek reconsideration or reinvestigation, identify every disputed item, and give the supporting facts and legal grounds for each one.

If you choose reinvestigation because you will present newly discovered or additional evidence, submit all relevant supporting documents within 60 days from filing the protest. Missing the 30-day protest deadline—or the 60-day document deadline for reinvestigation—can make the assessment final, executory, and demandable.

A reply to a Preliminary Assessment Notice (PAN) is different. It is generally due within 15 days from receipt and should be used to correct the proposed findings, but the formal administrative protest under Section 228 of the Tax Code is directed against the FLD/FAN.

These deadlines are strict. Record the actual date and manner of receipt, count conservatively, and file early.

Identify what the BIR sent you

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

Document or event	What it generally means	Immediate response
Letter of Authority or audit request	The BIR is examining specified tax periods and taxes	Verify the authority, assigned officers, scope, and requests; organize records
Notice of Discrepancy or similar audit communication	The BIR is presenting preliminary audit issues	Attend or respond within the period stated; reconcile each discrepancy
Preliminary Assessment Notice	Proposed deficiency assessment	Reply within 15 days from receipt, with facts and documents
Formal Letter of Demand and Final Assessment Notice	Formal assessment and demand for payment	File a valid protest within 30 days from receipt
Final Decision on Disputed Assessment	Decision on the protest	Appeal administratively or to the CTA, as applicable, within 30 days
Collection letter, Final Notice Before Seizure, warrant of distraint or levy, or garnishment	Collection is being demanded or enforced	Obtain tax counsel immediately; court deadlines and collection remedies may already be running

Read the complete packet, including schedules, Details of Discrepancies, annexes, envelopes, registry notices, and proof of electronic or personal service. The substance controls: a document labeled “final” may have serious consequences even if it is not called an FDDA.

The assessment-protest timeline

The principal rules appear in Section 228 of the National Internal Revenue Code and Revenue Regulations No. 18-2013, which amended Revenue Regulations No. 12-99.

1. Reply to the PAN within 15 days

The taxpayer generally has 15 days from receipt of the PAN to respond. The reply should address every proposed adjustment and attach the records already available.

A PAN is generally required before the FLD/FAN. Section 228 allows the BIR to proceed without one only in these cases:

A deficiency results from a mathematical error appearing on the face of the return.
There is a discrepancy between tax withheld and tax actually remitted by the withholding agent.
A taxpayer claimed a refund or tax credit for excess creditable withholding tax and also carried over and applied the same amount to succeeding estimated tax liabilities.
Excise tax on excisable articles was not paid.
An article bought or imported by an exempt person was sold, traded, or transferred to a non-exempt person.

Outside these exceptions, failure to issue and properly serve a PAN—or issuing the FAN before the taxpayer’s 15-day response period has expired—may violate due process. The Supreme Court has treated the PAN as a substantive safeguard, not a disposable formality, as illustrated in Yumex Philippines Corporation v. Commissioner of Internal Revenue.

Even when a PAN reply is optional in the sense that failing to submit one does not eliminate the later right to protest a timely received FLD/FAN, ignoring it wastes the first opportunity to correct the audit findings.

2. Protest the FLD/FAN within 30 days

The 30-day period runs from receipt of the FLD/FAN, not from its printed date. Exclude the date of receipt and begin counting the following day. Treat the period as calendar days and file well before the last day.

A protest should state:

The taxpayer’s registered name, TIN, address, and contact details.
The assessment number, date, taxable period, tax type, and date and manner of receipt.
Whether the protest covers the entire assessment or only specified portions.
Whether the remedy is reconsideration or reinvestigation.
The facts supporting the objection to each assessment issue.
The applicable statutes, regulations, and jurisprudence for each objection.
The amount disputed under each issue, with a reconciliation where possible.
The relief requested, such as cancellation or reduction of the assessment.
A numbered list of supporting documents.
The taxpayer’s or authorized representative’s signature and proof of authority.

A general statement that the assessment is “incorrect,” “unfair,” or “unsupported” is dangerous. Under Revenue Regulations No. 18-2013, an issue for which the taxpayer fails to state supporting facts and legal grounds may be treated as undisputed. Any genuinely undisputed portion may become final and collectible even while the remaining issues are contested.

3. Choose the correct kind of protest

Request for reconsideration

Choose reconsideration when the BIR can decide the case from records already available and you do not intend to introduce newly discovered or additional evidence.

It may involve questions of fact, law, or both. The separate 60-day document-submission period does not apply. For purposes of the BIR’s 180-day action period, the count generally begins from filing of the protest.

Request for reinvestigation

Choose reinvestigation when you intend to submit newly discovered or additional evidence, such as missing withholding certificates, corrected reconciliations, third-party confirmations, contracts, ledgers, or proof of payment not previously evaluated.

The protest must identify the additional evidence you intend to present. Submit all relevant supporting documents within 60 days from filing the protest. Evaluation may be confined to documents submitted within that period.

Do not casually request reinvestigation merely to gain time. The choice has procedural consequences, and a reinvestigation that the Commissioner grants can affect the prescriptive period for collection under Section 223 of the Tax Code.

The two remedies are alternatives at the FLD/FAN stage. Revenue Memorandum Order No. 26-2016 states that a protest is treated as reconsideration unless it clearly identifies itself as a request for reinvestigation.

Where and how to file

Follow the filing instructions in the FLD/FAN and verify the correct receiving office before the deadline. Do not assume that submission to the investigating revenue officer, an unrelated RDO, or a general BIR email address is valid.

Under Revenue Memorandum Circular No. 39-2013, the protests it covers must be filed by the taxpayer or authorized representative, personally or through registered mail with return card, with the office of the Regional Director, Assistant Commissioner–Large Taxpayers Service, or Assistant Commissioner–Enforcement Service that signed the relevant notice.

Preserve:

A complete signed copy of the protest and every attachment.
The BIR receiving stamp showing the office, date, and time.
If mailed, the registry receipt, return card, tracking record, and exact copy of the package.
An attachment index and page count.
Proof that the signer was authorized.
Photographs or scans of envelopes and notices showing delivery details.
Any written confirmation from the receiving office.

Do not rely solely on an informal acknowledgment from a revenue officer. If using registered mail, allow enough time to correct a rejected or misaddressed submission.

As of the source check date, RMC No. 35-2026 provides that, while the BIR’s applicable energy-conservation work arrangement remains effective, a deadline falling on a Friday for filing a request for reconsideration of an FDDA at the National Office moves to the next business day when personnel are working on-site. This limited rule should not be treated as a general extension of other protest or court deadlines.

Build the protest issue by issue

Use a separate section for each assessment finding. A practical structure is:

BIR finding and amount. Reproduce the issue accurately without unnecessarily conceding it.
Material facts. Give dates, transactions, accounting treatment, and amounts supported by records.
Why the finding is wrong. Explain the factual, computational, or legal error.
Evidence. Identify the exact exhibit supporting each statement.
Requested adjustment. Show the corrected computation and amount, if any.

Check, where supported by the actual record, for the following:

Computational and payment errors

Reconcile the assessment against returns, amended returns, payment confirmations, withholding certificates, alphalists, VAT schedules, ledgers, and audited financial statements. Look for duplicate adjustments, transposed amounts, payments applied to the wrong period, and credits the BIR did not recognize.

Incorrect tax treatment

Review the statute and regulations in force during the assessed period. A current rule should not automatically be applied to an older transaction, and a later amendment may not govern earlier taxable periods.

Missing factual and legal bases

The PAN and FLD/FAN must inform the taxpayer in writing of the facts and law, rules, regulations, or jurisprudence supporting the assessment. A bare table of amounts may be insufficient. The assessment must also make a definite demand for a determinable liability.

The Supreme Court explains the due-process requirement in Commissioner of Internal Revenue v. Liquigaz Philippines Corporation. A defective FDDA may itself be void without necessarily erasing an otherwise valid underlying assessment, so the effect depends on which document and stage are defective.

Improper or premature service

Review where, how, and upon whom the LOA, PAN, FLD/FAN, and FDDA were served. Service to an accredited tax agent may count as service to the taxpayer. Conversely, a receiving stamp alone may not prove valid personal service if the recipient and authority are not established.

Do not deliberately refuse delivery. Keep the BIR registration address current. Service disputes are highly fact-dependent, as shown in Commissioner of Internal Revenue v. Fort Bonifacio Development Corporation.

Lack of audit authority

Identify the revenue officers who actually examined the books and made the findings. Their authority should flow from a valid Letter of Authority covering the taxpayer, period, and investigation. If the case was transferred to different officers, verify whether the required authority was issued. The Supreme Court discusses this requirement in Commissioner of Internal Revenue v. McDonald’s Philippines Realty Corporation.

Prescription

As a general rule, internal revenue taxes must be assessed within three years after the last day prescribed for filing the return, or from actual filing if the return was filed late. A return filed early is treated as filed on its statutory due date.

Important exceptions include a false or fraudulent return with intent to evade tax, failure to file a return, a valid written waiver made before the applicable period expires, and statutory grounds that suspend the period. Fraud is not presumed merely because the BIR alleges a discrepancy. Prescription calculations require the returns, filing dates, waivers, service records, and relevant suspensions.

Penalties and taxpayer classification

Check whether surcharge, interest, and other penalties were computed under the law applicable to the taxpayer and period. Under the Ease of Paying Taxes rules, a business taxpayer is generally classified as:

Micro: annual gross sales below ₱3 million.
Small: ₱3 million to below ₱20 million.
Medium: ₱20 million to below ₱1 billion.
Large: ₱1 billion or more.

Gross sales for classification are determined under Revenue Regulations No. 8-2024, and the taxpayer’s actual BIR classification or reclassification must be checked. Revenue Regulations No. 6-2024 provides reduced civil-penalty and interest rates for covered micro and small taxpayers. Whether those concessions apply to a particular assessment depends on the taxpayer’s classification, the violation, and the relevant period.

What happens after the protest

If the BIR issues an FDDA

Read who signed it.

If the FDDA was issued by the Commissioner’s duly authorized representative, the taxpayer generally has 30 days from receipt to choose between:

Filing a petition for review with the Court of Tax Appeals; or
Elevating the protest to the Commissioner through a request for reconsideration.

An administrative appeal to the Commissioner is limited to reconsideration. A new reinvestigation is not available at this stage, and only issues addressed in the representative’s decision will be entertained.

If the Commissioner personally denies the protest or administrative appeal, the remedy is generally a petition for review with the CTA within 30 days from receipt. Filing another motion for reconsideration with the Commissioner does not suspend that court deadline.

Under RMC No. 43-2023, a taxpayer appealing an FDDA must also furnish the specified Assessment Division or Large Taxpayers/Enforcement office with a copy of the appeal within five days from filing it with the Office of the Commissioner or the CTA.

If the BIR does not act within 180 days

For reconsideration, the 180-day period generally runs from filing of the protest. For reinvestigation, it runs from submission of the required supporting documents within the 60-day period.

After the 180 days expire, the taxpayer generally has two mutually exclusive choices:

Appeal the BIR’s inaction to the CTA within the next 30 days; or
Continue waiting for a final decision, then appeal that decision within 30 days from receipt.

Choosing the first route bars reliance on the second. If the taxpayer waits, the assessment does not become final merely because no CTA petition was filed immediately after the 180 days. This rule is explained in Lascona Land Co., Inc. v. Commissioner of Internal Revenue.

The correct starting date for the 180 days can be disputed, particularly when documents were submitted in batches or an administrative appeal followed an FDDA. Fix that date from stamped records before choosing a remedy.

Do not ignore collection action

A collection letter, Final Notice Before Seizure, warrant, garnishment, tax lien, or collection case requires immediate legal review. Depending on its language and the procedural history, collection action may be treated as an express or implied denial that starts a 30-day CTA period. In other circumstances, collection may be premature because a valid administrative appeal remains pending.

A CTA appeal does not automatically suspend collection. Section 11 of Republic Act No. 9282 allows the CTA to suspend collection when it may jeopardize the interests of the government or taxpayer, generally subject to a cash deposit or acceptable surety bond of no more than twice the amount claimed. A motion for suspension requires evidence; it is not granted simply because an assessment is disputed.

Evidence to preserve

Keep an audit-and-protest file containing:

All filed tax returns, amendments, attachments, and filing confirmations.
Proof of tax payments and remittances.
Books, ledgers, journals, trial balances, and audited financial statements.
Sales invoices and other source documents.
Contracts, purchase orders, delivery records, and bank documents.
Withholding certificates, alphalists, and reconciliations.
The LOA and proof of authority for any replacement revenue officer.
Every BIR notice, schedule, annex, envelope, and service record.
Minutes or notes of conferences with BIR personnel.
All submissions to the BIR with stamped proof of receipt.
Board resolutions, special powers of attorney, or other authority documents.
A deadline sheet showing receipt, filing, document-submission, 180-day, and appeal dates.

Preserve original files and metadata. Work from copies, and keep an off-site or secure digital backup.

Common mistakes

Treating a PAN reply as the protest against the FLD/FAN.
Counting 30 days from when management or the external accountant finally reads the notice instead of the legally relevant receipt date.
Sending only a request for “more time” instead of a complete, valid protest.
Failing to specify reconsideration or reinvestigation.
Choosing reinvestigation but missing the 60-day document deadline.
Disputing the total amount without addressing each adjustment separately.
Omitting facts and legal grounds for one of several assessment issues.
Filing with the investigating officer instead of the proper receiving office.
Relying on ordinary email or informal delivery without an authorized filing channel and proof of receipt.
Assuming settlement discussions, a compromise application, or partial payment stops a protest or appeal deadline.
Filing another motion with the Commissioner after the Commissioner’s denial and assuming it tolls the CTA period.
Waiting for an FDDA after receiving a collection document whose language may already amount to a denial.
Assuming a CTA petition automatically stops garnishment, levy, or other collection.

When professional help is urgent

Consult a Philippine tax lawyer immediately if:

Fewer than five days remain before a 15-, 30-, or 60-day deadline.
An FDDA or collection notice has arrived.
The BIR has issued a warrant of distraint or levy, garnishment, tax lien, or notice of seizure.
The assessment alleges fraud, willful non-filing, falsified invoices, or possible criminal liability.
Receipt or service is disputed.
The audit was handled by officers not clearly named in the LOA.
Waivers of the assessment period were signed.
The BIR assessed several taxes or taxable periods using interdependent computations.
Paying or securing the assessment would threaten payroll, operations, property, or banking relationships.
A CTA petition or motion to suspend collection may be necessary.

A CPA can reconstruct the computation and evidence, while tax counsel should control jurisdictional deadlines, legal grounds, and CTA strategy. For substantial assessments, coordinated legal and accounting work is usually necessary.

Frequently asked questions

Can I protest a PAN?

You may and usually should reply to it within 15 days, but the Section 228 administrative protest is filed against the FLD/FAN. If the BIR issues an FLD/FAN despite your PAN reply, file a new, valid protest within 30 days.

Must I pay the assessment before protesting?

Generally, prepayment is not required to file the administrative protest or a petition for review involving a disputed BIR assessment. However, interest and applicable penalties may remain at issue, and a CTA appeal does not automatically suspend collection.

Which is better: reconsideration or reinvestigation?

Use reconsideration if the existing record is sufficient. Use reinvestigation if additional or newly discovered evidence is genuinely necessary and can be completely submitted within 60 days. The better choice depends on the audit record, evidence, prescription issues, and litigation strategy.

Can the 30-day protest period be extended?

Do not assume so. The 30-day period is mandatory, and failure to file a valid protest can make the assessment final. File the substantive protest on time even if some internal analysis is still being completed, while ensuring that the selected remedy and required grounds are properly stated.

Can I submit documents after the 60-day reinvestigation period?

Do not rely on late submission. The BIR may restrict its evaluation to documents submitted within the 60 days, and failure to submit the relevant documents on time may make the assessment final.

What if I agree with only part of the assessment?

Clearly identify the agreed and disputed portions. An undisputed portion may become final and collectible. Coordinate payment using the BIR’s current prescribed form and channel, and preserve proof that payment relates only to the accepted portion.

What if the BIR remains silent after 180 days?

You may appeal the inaction to the CTA within 30 days after the 180-day period expires, or wait for the final decision and appeal within 30 days from receipt. These remedies are mutually exclusive. Have counsel confirm the correct start and end dates before electing either route.

Can I file the protest by email?

Do not assume that ordinary email is valid. Follow the notice and current BIR issuance governing the receiving office and method. RMC No. 39-2013 recognizes personal filing and registered mail with return card for the protests it covers.

Does a defective assessment disappear automatically?

No. Raise the defect in a timely protest and preserve the evidence. Different defects have different effects: a void FLD/FAN, a defective FDDA, improper service, lack of audit authority, and prescription are not interchangeable.

Can I negotiate a compromise instead?

The Commissioner has limited authority under Section 204 of the Tax Code to compromise qualifying liabilities, including where reasonable doubt exists as to the claim’s validity or the taxpayer demonstrates financial incapacity. Approval is not automatic, and a compromise request should not be treated as a substitute for a timely protest or CTA appeal.

This article provides general Philippine legal information, not legal or tax advice for a particular assessment. Outcomes depend on the notices, service records, taxable periods, evidence, and procedural history. Statutes, BIR issuances, CTA rules, and Supreme Court authorities were checked through official sources as of August 3, 2026.