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. File it with the office of the Commissioner or duly authorized BIR official who signed the FLD/FAN—not merely with the examining revenue officer or an unrelated RDO.

The protest must:

Identify whether it is a request for reconsideration or request for reinvestigation;
State the assessment date and every item being disputed;
Explain the relevant facts and the applicable law, regulations, or jurisprudence for each disputed item; and
If requesting reinvestigation, identify the additional evidence to be presented and submit all relevant supporting documents within 60 days from filing the protest.

Missing the 30-day protest period, filing with the wrong office, submitting a vague protest, or leaving an assessment item unanswered can make all or part of the assessment final, executory, and demandable. The controlling rules are Section 228 of the National Internal Revenue Code and Revenue Regulations No. 18-2013.

First identify the notice you received

Not every BIR letter is already a protestable final assessment.

Document	What it generally means	Immediate action
Letter of Authority or electronic LOA	Authority to examine specified records, periods, and taxes	Verify its scope, issuing authority, assigned officers, and service
Notice of Discrepancy	Audit findings for discussion before assessment	Reconcile the findings and respond within the period stated in the notice
Preliminary Assessment Notice (PAN)	Proposed assessment	Respond within 15 days from receipt
FLD/FAN	Formal deficiency assessment and demand for payment	File the Section 228 protest within 30 days from receipt
Final Decision on Disputed Assessment (FDDA)	Decision on the protest	Appeal within the applicable 30-day period
Collection letter, final notice before seizure, warrant, or garnishment	Possible collection action or denial of a pending protest	Obtain legal help immediately; it may trigger a court deadline

A response to a PAN is not the same as the formal protest against an FLD/FAN. BIR guidance treats a PAN response as optional rather than a mandatory administrative remedy, but responding within 15 days is normally advisable because it may correct issues before a final assessment is issued. Failure to answer a PAN does not eliminate the right to protest a later FLD/FAN within 30 days.

This procedure applies principally to deficiency assessments. Collection of an unpaid tax already declared in the taxpayer’s own return, denial of a refund, customs duties, and local taxes may follow different rules.

Calendar every deadline from actual receipt

Record the exact date and manner of receipt immediately. Day 1 is generally the day after receipt.

The key periods are:

Event	General period
Response to PAN	15 days from receipt
Protest against FLD/FAN	30 days from receipt
Supporting documents for a request for reinvestigation	60 days from filing the protest
BIR action on a request for reconsideration	180 days from filing the protest
BIR action on a request for reinvestigation	180 days from submission of the required supporting documents
CTA appeal from FDDA or other final denial	30 days from receipt
CTA appeal based on BIR inaction	30 days after the applicable 180-day period expires

If the last day falls on a Saturday, Sunday, or legal holiday, time-computation rules may move the deadline to the next working day. Specific BIR issuances may also extend deadlines during officially declared government-work suspensions or disasters. Nevertheless, file early and do not rely on a verbal extension, an informal discussion with the examiner, or an assumption that an office closure automatically changes the deadline.

Preserve the envelope, registry notice, return card, courier record, receiving log, email notice, and any document showing who accepted the notice and when. Under RR No. 18-2013, service may be personal, substituted, or by mail or professional courier. Service on a properly appointed tax agent may be treated as service on the taxpayer.

Choose the correct kind of protest

Request for reconsideration

A request for reconsideration asks the BIR to re-evaluate the assessment using the records already available. It is generally appropriate when the dispute involves:

A legal interpretation;
A computational error evident from existing records;
Evidence already submitted during the audit;
The validity of the assessment process; or
An issue of law and fact that does not require new evidence.

The separate 60-day document-submission period does not apply to a request for reconsideration.

Request for reinvestigation

A request for reinvestigation asks the BIR to re-evaluate the assessment using newly discovered or additional evidence. Use it when you intend to submit further contracts, invoices, withholding certificates, reconciliations, accounting schedules, bank records, or other supporting materials.

The protest must identify the additional evidence you intend to present. Submit all relevant documents within 60 days from filing the protest. The Supreme Court confirmed in CIR v. Maxicare Healthcare Corporation that this 60-day period applies to a reinvestigation request against the FLD/FAN—not to a PAN response—and that the taxpayer must be given the full opportunity to submit the promised evidence.

If the protest does not clearly request reinvestigation, BIR rules generally treat it as a request for reconsideration. The two remedies should not be combined casually: BIR guidance states that choosing one precludes filing the other at that stage.

Prepare a protest that is valid for every assessment item

There is no substitute for an issue-by-issue protest. A useful structure is:

Addressee and filing office. Address the protest to the Commissioner or authorized official who signed the FLD/FAN.
Taxpayer information. State the registered name, TIN, registered address, contact details, and authorized representative.
Assessment details. Identify the FLD/FAN number, assessment date, taxable period, tax types, amounts, and date of receipt.
Nature of the protest. Clearly state “request for reconsideration” or “request for reinvestigation.”
Complete statement of disputed items. List every tax type, adjustment, surcharge, interest computation, and other item being challenged. State expressly if the entire assessment is disputed.
Facts for each issue. Explain what occurred and identify the relevant returns, books, transactions, payments, or audit records.
Legal grounds for each issue. Cite the applicable Tax Code provision, regulation, official issuance, or controlling decision and explain how it applies. A citation without an explanation may not adequately dispute the item.
Computations. Supply corrected schedules and reconciliations where the dispute involves amounts.
Evidence. Identify each attachment by issue. For reinvestigation, specify any additional evidence that will be submitted within the 60-day period.
Requested relief. Ask for cancellation or reduction of the identified assessment items and issuance of the appropriate decision.
Signature and authority. The taxpayer or properly authorized representative should sign. Attach the relevant special power of attorney, secretary’s certificate, board authorization, or other proof of authority when applicable.
Attachment index. Number the documents and keep an identical copy of the entire filing.

A bare statement that the assessment is “unjust,” “excessive,” or “without basis” is dangerous. Under RR No. 18-2013, a protest that omits the required legal basis may be considered void. Any issue not specifically disputed with its factual and legal basis may be treated as an undisputed assessment that has become final and collectible.

File with the correct BIR office and preserve proof

Under RMC No. 39-2013 and RMC No. 11-2014, the protest should be filed with the office of the Commissioner’s authorized representative who signed the FLD/FAN. An administrative appeal from that official’s adverse decision is filed with the Office of the Commissioner.

The established BIR filing channels for an FLD/FAN protest are:

Personal filing by the taxpayer or duly authorized representative; or
Registered mail with return card.

For personal filing, obtain a date-stamped receiving copy showing the office, receiver, and complete list of attachments. For registered mail, retain the registry receipt, return card, tracking record, mailing envelope, and a complete copy of the package. Do not rely only on ordinary email, an unacknowledged handoff to the revenue officer, or filing at a convenient but unauthorized BIR office.

If using a representative, verify that the authorization covers receipt of notices, filing of protests, submission of evidence, and administrative appeals.

Pay or expressly protest every portion

A taxpayer may accept and pay part of an assessment while disputing the remainder. Clearly identify:

The items accepted;
The items paid;
The items disputed; and
How the corresponding amounts were computed.

Under RR No. 18-2013, an unprotested item becomes final, executory, and demandable even if other items are properly disputed. Keep the filed payment form and proof of payment for any accepted portion.

Payment does not automatically cure a missed protest or preserve a challenge. Obtain advice before paying a disputed amount, entering a compromise, signing a waiver, or withdrawing a protest because each step can affect available remedies.

Review both the merits and the validity of the assessment

Possible grounds should be raised only when supported by the documents and applicable law. They may include:

Incorrect facts or computations

Examples include duplicated income, uncredited tax payments, incorrect withholding-tax credits, erroneous reconciliation of sales, expenses attributed to the wrong period, or penalties calculated from an incorrect base.

Incorrect tax treatment

The BIR may have applied the wrong tax type, rate, classification, source rule, exemption, deduction rule, or taxable period. State the correct treatment and provide the necessary records.

Prescription

The BIR generally has three years to assess, counted under Section 203 of the Tax Code. A ten-year period may apply to a false or fraudulent return with intent to evade tax or a failure to file a return. A valid written waiver may also extend the assessment period. The exact computation depends on filing dates, service of the assessment, allegations of fraud, waivers, and any legally recognized suspension. The Supreme Court discusses these rules in CIR v. Fitness by Design, Inc..

Defective notice or denial of due process

Section 228 requires the taxpayer to be informed in writing of the facts and law supporting an assessment. An FLD/FAN that merely demands a figure without adequately stating its factual and legal basis may be void. An FDDA must likewise state its factual and legal grounds and clearly communicate that it is the final decision. The effect of a defective FDDA is not always the same as the effect of a defective assessment, as explained in CIR v. Liquigaz Philippines Corporation.

Other potential defects include:

Failure to issue a PAN when one was required;
Failure to give the full 60-day evidence period after a proper request for reinvestigation;
Invalid or unproven service;
Examination by an officer without proper audit authority;
Assessment beyond the authorized tax type or taxable period; or
Materially different findings introduced without adequate written explanation.

These are fact-sensitive defenses. Raise them in the protest instead of simply ignoring the assessment.

When a PAN is not required

The general rule is that the BIR must issue a PAN before the FLD/FAN. Section 228 recognizes exceptions where the BIR may issue an FLD/FAN outright:

A mathematical error appearing on the face of the return;
A discrepancy between tax withheld and the amount actually remitted;
Carryover of an excess creditable-withholding-tax amount that was also claimed as a refund or tax credit;
Unpaid excise tax on excisable articles; or
Transfer to a non-exempt person of an article locally purchased or imported by an exempt person.

The absence of a PAN is therefore not automatically fatal. Determine first whether the assessment falls within a statutory exception.

Special rule for a consolidated FAN issued under the 2026 audit framework

BIR RMO No. 6-2026 introduced safeguards for consolidating certain pending audits under the Single-Instance Audit Framework. Where consolidation at the FAN stage is legally permitted, the Consolidated FAN must expressly supersede the prior notice and provide a fresh 30-day protest period from receipt.

Do not assume that every revised, amended, or repeated demand automatically restarts the deadline. Confirm that the notice is a valid Consolidated FAN covered by RMO No. 6-2026 and that the prescribed safeguards were followed. Consolidation is not allowed once a FAN has already become final and executory or the case has reached the FDDA stage.

What happens after the protest

If the protest is denied by an authorized representative

If an FDDA is 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 cannot be a request for reinvestigation, and only the issues addressed in the authorized representative’s decision will be entertained. Do not assume that the administrative appeal gives the Commissioner a new, separate 180-day period.

If the Commissioner denies the protest

If the denial is issued by the Commissioner, the remedy is generally an appeal to the CTA within 30 days from receipt. Filing another motion for reconsideration with the Commissioner does not stop or restart the CTA’s 30-day period.

If the BIR does not act within 180 days

The reckoning date depends on the protest:

Reconsideration: from filing the protest;
Reinvestigation: from submission of the required supporting documents.

After the 180-day period expires, the taxpayer has two mutually exclusive options:

Appeal the inaction to the CTA within the next 30 days; or
Wait for the final BIR decision, then appeal within 30 days from receipt.

The Supreme Court confirmed these alternatives in Lascona Land Co., Inc. v. CIR. Once the taxpayer chooses to appeal the inaction, the taxpayer cannot later rely on the option to await a decision.

Waiting is not risk-free. A collection letter, warrant, or similarly unequivocal communication may be treated as a denial or final determination in some circumstances. Obtain immediate advice whenever collection action begins while a protest or administrative appeal is pending.

Appealing to the Court of Tax Appeals

A CTA appeal is commenced by a petition for review under Rule 8 of the Revised Rules of the Court of Tax Appeals. The basic period is 30 days from receipt of the appealable decision or from expiration of the statutory period for BIR action.

The CTA may, for good cause and upon compliance with the applicable motion-and-fee requirements, grant an additional period not exceeding 15 days. This extension is discretionary and should not be treated as part of the ordinary deadline.

CTA filing currently involves strict paper and electronic-submission requirements. Depending on the chosen primary mode, filing may be personal, by registered mail, by accredited courier, or electronically, with corresponding electronic or paper copies due within the periods prescribed by CTA En Banc Resolution No. 8-2024 and CTA En Banc Resolution No. 1-2025. A required electronic copy that is not transmitted on time can cause a pleading to be treated as not filed.

An appeal does not automatically suspend collection. Under Republic Act No. 9282, the CTA may suspend collection when justified and may require a cash deposit or surety bond of up to twice the amount claimed.

Because CTA jurisdiction and filing periods are strictly applied, engage Philippine tax counsel well before the 30-day deadline.

Evidence to preserve

Keep one complete, indexed assessment file containing:

LOA or eLA and proof of service;
Notice of Discrepancy, PAN, FLD/FAN, FDDA, and collection notices;
Envelopes, registry records, return cards, courier tracking, and receiving logs;
All responses, protest letters, transmittals, and stamped receiving copies;
Tax returns, proof of filing, and proof of payment;
Audited financial statements and books of accounts;
General ledgers, subsidiary ledgers, journals, and trial balances;
Invoices, contracts, payroll records, bank records, and withholding certificates;
Reconciliation and corrected-computation schedules;
BIR requests, subpoenas, meeting minutes, and email correspondence;
Waivers of prescription and related acceptance records;
Proof of authority of every representative; and
A chronology showing every receipt, filing, submission, and deadline.

Do not surrender the only available original unless legally required. Keep an exact copy and obtain a detailed acknowledgment for documents presented to the BIR.

Common mistakes

Treating a PAN response as the formal protest against the FLD/FAN;
Counting the deadline from the notice date instead of the receipt date—or failing to preserve proof of receipt;
Filing with the revenue officer or wrong BIR office;
Relying on verbal discussions, ordinary email, or an informal request for more time;
Failing to state whether the request is for reconsideration or reinvestigation;
Requesting reconsideration while intending to submit new evidence;
Missing the 60-day reinvestigation document deadline;
Disputing the total amount without addressing every assessment issue;
Citing provisions without explaining how they apply to the facts;
Failing to pay or expressly protest an undisputed portion;
Assuming a revised letter automatically restarts the 30-day period;
Filing another motion with the Commissioner and assuming it suspends the CTA deadline;
Assuming CTA review automatically stops collection; or
Missing the CTA’s electronic-copy, docket-fee, or paper-copy requirements.

When legal help is urgent

Seek Philippine tax counsel immediately if:

The FLD/FAN protest deadline is less than 10 days away;
You received an FDDA, final demand, warrant of distraint or levy, garnishment notice, or collection summons;
The BIR alleges fraud, willful failure, or criminal liability;
Receipt or service of an assessment is disputed;
A bank account, receivable, or property is threatened with collection;
The assessment covers several tax types, taxable years, or a substantial amount;
The 60-day evidence period or 180-day inaction period is about to expire;
You intend to appeal to the CTA;
You received a Consolidated FAN under the 2026 audit framework; or
You are being asked to sign a waiver, compromise, admission, or withdrawal.

FAQ

Can I protest a PAN?

You may respond to a PAN within 15 days, but the formal administrative protest under Section 228 is directed against the FLD/FAN. A PAN response does not replace the 30-day FLD/FAN protest.

Is there a required BIR protest form?

The governing rules contemplate a written protest rather than a standard numbered tax form. The letter must satisfy the required content, authority, venue, and deadline rules.

Can I ask for both reconsideration and reinvestigation?

BIR guidance treats them as alternative remedies. Choose reinvestigation if additional evidence will be presented; otherwise, reconsideration may be appropriate.

Can I submit reinvestigation documents after 60 days?

The rules require all relevant supporting documents within 60 days from filing the protest. Late documents may be rejected, and the assessment may become final as to the attempted introduction of additional evidence.

What if only one part of the assessment is wrong?

Protest that part specifically and address every related factual and legal issue. Pay or clearly identify any accepted portion. Unprotested items may become final and collectible.

Does BIR silence automatically cancel the assessment?

No. After the applicable 180-day period, you may appeal the inaction to the CTA within 30 days or wait for a final BIR decision. The choice and deadline must be managed carefully.

Does filing at the CTA stop garnishment or collection?

No. A CTA appeal does not automatically suspend collection. The taxpayer may need to request suspension and comply with any deposit or bond ordered by the Court.

What if the BIR skipped the PAN?

A PAN is generally required, but Section 228 contains five specific exceptions. Review whether an exception applies before asserting that the assessment is void.

Official references

This article provides general Philippine legal information, not legal or tax advice for a particular assessment. Results depend on the notices, proof of service, audit authority, taxable periods, records, and procedural choices involved. Official sources and procedures were checked as of August 4, 2026.