Quick answer

To contest a BIR deficiency tax assessment, file a 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 BIR official who issued the FLD/FAN—not merely with the revenue officer who conducted the audit.

The protest must identify every disputed issue, state whether it is a request for reconsideration or request for reinvestigation, and explain the supporting facts and legal grounds. A general statement that the assessment is “incorrect” is not enough. Any issue left undisputed, or unsupported by facts and law, may become final and collectible.

If you choose reinvestigation, submit all additional supporting documents within 60 days from filing the protest. Depending on how the BIR acts—or fails to act—you may later appeal to the Court of Tax Appeals (CTA), usually within another strict 30-day period.

These deadlines can determine the entire case. Record the actual date and manner in which every BIR notice was received, and obtain tax counsel immediately if the 30-day protest period is already running.

Know which BIR document you received

Not every audit document starts the 30-day protest period.

Document or stage	What it means	Usual response period
Notice of Discrepancy or notice for informal conference	The BIR is presenting audit findings and giving the taxpayer an opportunity to explain	The informal-conference process generally may not extend beyond 30 days from receipt
Preliminary Assessment Notice (PAN)	Proposed deficiency assessment	Respond within 15 days from receipt
Formal Letter of Demand and Final Assessment Notice (FLD/FAN)	Formal assessment and demand for payment	File an administrative protest within 30 days from receipt
Final Decision on Disputed Assessment (FDDA)	Decision on the protest	Take the proper administrative appeal or file with the CTA within 30 days, as applicable
Collection letter, final notice before seizure, warrant of distraint or levy	Collection action may be underway	Obtain legal help immediately

The informal-conference procedure is governed by Revenue Regulations No. 7-2018. The PAN, FLD/FAN, protest, and FDDA rules appear principally in Revenue Regulations No. 18-2013, which amended Revenue Regulations No. 12-99.

Do not mistake a PAN response for the formal protest

You should answer a PAN within 15 days, but the PAN response ordinarily is not the administrative protest required by Section 228 of the National Internal Revenue Code. The document that must ordinarily be protested within 30 days is the later FLD/FAN.

A timely PAN response also does not eliminate the need to file a separate, timely protest when the FLD/FAN arrives.

When the BIR may issue an FLD/FAN without a PAN

Section 228 permits an assessment without a PAN in specified cases, including:

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 for refund or tax credit;
Unpaid excise tax on excisable articles; and
A transfer to a non-exempt person of an article acquired tax-free by an exempt person.

Outside the statutory exceptions, failure to provide the required PAN and opportunity to respond may present a due-process issue. Whether that defect invalidates a particular assessment depends on the notices, dates, method of service, and applicable law.

Step 1: Establish the exact date of receipt

The 30-day period runs from receipt of the FLD/FAN, not simply from the date printed on it.

Immediately preserve:

The complete FLD/FAN and every attached assessment notice or computation;
The envelope, postmark, registry notice, registry return card, courier record, or proof of personal service;
The name, position, and authority of the person who received it;
The date and time of receipt;
Photographs or scans of the documents as originally received; and
Any dispute concerning service, an outdated address, missing pages, or receipt by an unauthorized person.

Do not assume that the period means 30 working days. Do not rely on an oral assurance that an extension will be granted. Have the last filing date calculated conservatively, including the effect of weekends, holidays, office closures, and the particular filing method.

Step 2: Choose reconsideration or reinvestigation

The protest must expressly identify its nature.

Request for reconsideration

A request for reconsideration asks the BIR to reevaluate the assessment using the records already submitted before the FLD/FAN was issued.

This is usually appropriate when the dispute concerns matters such as:

An error in the BIR’s computation;
Misapplication of a tax law or regulation;
Failure to credit a payment or withholding tax;
A legal or due-process defect apparent from the existing record; or
Documents already in the audit docket that the BIR allegedly overlooked.

Under the current BIR regulation, the separate 60-day supporting-document period does not apply to reconsideration in the same way that it applies to reinvestigation. Nevertheless, the protest should be as complete as possible when filed.

Request for reinvestigation

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

All relevant supporting documents must be submitted within 60 days from filing the protest. Missing that period may prevent the taxpayer from disputing the assessment through new or additional evidence and lead to denial of the protest.

Choose carefully. A request for reinvestigation may also have consequences for the limitation period when it is granted by the BIR. The best choice depends on the existing audit docket, the evidence still being obtained, and the defenses being raised.

Step 3: Prepare a valid, issue-by-issue protest

At minimum, the written protest should include:

The taxpayer’s complete name, TIN, registered address, and contact information;
The assessment number, date, taxable period, tax type, and amount involved;
The date and manner in which the FLD/FAN was received;
A clear statement that the taxpayer is protesting the FLD/FAN within the prescribed period;
The nature of the protest—reconsideration or reinvestigation;
For reinvestigation, a description of the newly discovered or additional evidence to be submitted;
A separate discussion of every disputed adjustment or assessment item;
The material facts relating to each issue;
The applicable statutes, regulations, and jurisprudence supporting each objection;
A reconciliation or corrected computation, where relevant;
The specific relief requested, such as cancellation or reduction of particular assessment items;
A numbered list of attachments; and
The signature of the taxpayer or properly authorized representative.

If the FLD/FAN contains several tax types or adjustments, address each one separately. Under RR No. 18-2013, an issue not disputed—or disputed without supporting facts and legal authority—may be treated as uncontested and become final, executory, and demandable.

Grounds that may require investigation

A protest should be based on the actual records. Possible issues commonly requiring review include:

The assessment does not adequately explain its factual and legal bases;
The PAN or other required due-process step was omitted;
The taxpayer was not given the prescribed opportunity to respond;
The figures do not reconcile with the return, books, withholding certificates, or payments;
Income, sales, purchases, or deductions were counted twice or assigned to the wrong period;
The BIR relied on an incorrect tax rate, tax base, characterization, or legal rule;
Valid tax credits or prior payments were not recognized;
The questioned transactions were exempt, zero-rated, already taxed, or not attributable to the taxpayer;
The records substantiate deductions, input tax, withholding credits, or other contested items;
The audit or assessment was issued outside the applicable limitation period;
A waiver extending the assessment period is absent, defective, expired, or does not cover the relevant tax and period;
The assessment was issued by an official without the required authority; or
The assessment differs materially from the findings previously disclosed without adequate explanation.

Section 228 requires the taxpayer to be informed in writing of the law and facts supporting the assessment. The Supreme Court has held that an assessment may be void when the FLD/FAN itself fails to provide the required bases; audit working papers do not necessarily cure that defect. See Commissioner of Internal Revenue v. Enron Subic Power Corporation.

An alleged defect should still be stated precisely. Not every procedural irregularity has the same legal effect, and some questions depend on proof of service, authority, prejudice, or substantial compliance.

Step 4: File with the correct BIR office

The protest should be addressed and filed with the office of the Assistant Commissioner, Regional Director, or other authorized higher revenue official who issued the FLD/FAN. BIR guidance allows administrative protests to be filed:

In person; or
By registered mail.

For registered mail, the post-office stamp on the envelope is treated as the filing date, and the envelope should form part of the case docket. Keep the original registry receipt, tracking records, and a complete copy of everything mailed.

For personal filing, bring an extra complete copy and obtain a receiving stamp showing the date, time, office, name or initials of the receiving employee, and number of pages or attachments.

Do not rely solely on ordinary email, an oral handover to the examining revenue officer, or an unverified private delivery method unless the BIR has given valid written instructions authorizing that method for the case. The relevant filing guidance appears in RMC No. 15-2020, Annex A and RMC No. 11-2014.

Step 5: Submit and preserve the supporting evidence

For reinvestigation, submit all relevant documents within 60 days from the protest date. Use an indexed submission identifying which documents support each disputed issue.

Evidence may include:

Filed tax returns and proof of filing;
Books of accounts, ledgers, journals, and trial balances;
Invoices, receipts, vouchers, contracts, purchase orders, and delivery records;
Bank statements and payment confirmations;
Withholding-tax certificates and schedules reconciling them with returns;
Importation, export, or customs documents;
Payroll and employee records;
Audited financial statements and working-paper reconciliations;
Prior BIR correspondence, submissions, and stamped receiving copies;
The Letter of Authority and any amendment or reassignment document;
Waivers of the statute of limitations;
Corporate authorizations and powers of attorney;
Affidavits from persons with direct knowledge, when appropriate; and
A corrected tax computation showing how the taxpayer arrives at the amount, if any, properly due.

Keep originals secure. Submit copies unless originals are specifically required, and maintain an exact digital copy of the filed set.

What happens after the protest

The 180-day BIR period

Under RR No. 18-2013:

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

Keep a written deadline calendar. The start date can be disputed when documents were submitted in stages or the BIR later asked for more material.

If an authorized BIR representative denies the protest

If an FDDA is issued by a duly authorized representative of the Commissioner, the taxpayer generally has two alternatives within 30 days from receipt:

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 request for reinvestigation is not allowed at this stage. Only the issues addressed in the authorized representative’s decision will ordinarily be entertained.

If the taxpayer appeals an FDDA either to the Commissioner or to the CTA, RMC No. 43-2023 requires a copy of the appeal to be furnished within five days to the Chief of the Assessment Division for a regional case, or to the concerned Head Revenue Executive Assistant for covered Large Taxpayers Service or National Investigation Division cases.

If the Commissioner denies the protest or administrative appeal

File the CTA petition within 30 days from receipt of the Commissioner’s decision. A motion asking the Commissioner to reconsider that denial does not stop or restart the 30-day CTA period.

If the BIR does not act within 180 days

The taxpayer has two mutually exclusive options:

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

The Supreme Court confirmed these alternatives in Lascona Land Co., Inc. v. Commissioner of Internal Revenue. Filing an appeal based on inaction constitutes a choice of the first remedy; the taxpayer cannot simultaneously wait for a later administrative decision on the same protest.

Because the correct 180-day starting point can be fact-sensitive, obtain a written deadline analysis before choosing either route.

Appealing to the Court of Tax Appeals

An appeal from a BIR decision or inaction is made by a petition for review filed with the CTA in Division. There is no minimum disputed amount for the CTA’s appellate review of a disputed BIR assessment.

Under the Revised Rules of the Court of Tax Appeals, the petition must generally:

Show why the CTA has jurisdiction;
Present a concise but complete statement of facts;
Identify the issues and grounds for review;
Be verified;
Contain the required certification against forum shopping;
Attach a clearly legible duplicate original or certified true copy of the appealed decision; and
Be accompanied by proof of payment of the docket and lawful fees.

Current CTA rules also impose paper and electronic-copy requirements. Initiatory pleadings must be filed through the authorized primary method, with the corresponding PDF transmitted to the CTA’s Judicial Records Division. Failure to submit the required electronic copy can result in the petition being treated as not filed. Check the CTA’s current filing page and CTA En Banc Resolution No. 1-2025 immediately before filing.

CTA litigation involves jurisdictional allegations, verification, service, docket fees, evidentiary rules, and strict electronic-filing requirements. A tax-litigation lawyer should prepare or review the petition.

A CTA appeal does not automatically stop collection

Filing a CTA petition does not, by itself, suspend payment, levy, distraint, or sale of the taxpayer’s property. If collection may jeopardize the taxpayer’s or the government’s interests, the taxpayer may ask the CTA to suspend collection.

The motion must be verified and supported by affidavits and documentary evidence. If suspension is warranted, the CTA may require a cash deposit equal to the value of the property or goods in dispute or an acceptable surety bond of up to twice the disputed amount or value. The governing provisions appear in Rule 10 of the Revised CTA Rules.

A warrant of distraint or levy, bank garnishment, or scheduled sale requires immediate legal action. Do not assume that a pending BIR protest or CTA case has automatically stopped collection.

Common mistakes that can make an assessment final

Answering the PAN but failing to protest the FLD/FAN;
Counting from the notice date without preserving proof of actual receipt;
Filing beyond the 30-day period;
Sending the protest only to the examining revenue officer;
Failing to identify the protest as reconsideration or reinvestigation;
Using a generic protest that does not discuss each adjustment;
Omitting one tax type, period, or issue from the protest;
Failing to submit reinvestigation documents within 60 days;
Submitting documents without an index or proof of receipt;
Assuming negotiations or settlement discussions extend a deadline;
Filing another motion with the Commissioner and assuming it tolls the CTA period;
Missing the five-day copy-furnishing requirement after an FDDA appeal;
Treating the 180-day rule as having only one possible remedy;
Assuming a CTA appeal automatically suspends collection; and
Ignoring current CTA paper-and-electronic filing requirements.

When legal help is urgent

Consult a Philippine tax lawyer immediately if:

The FLD/FAN protest deadline is less than a week away;
An FDDA has been received;
The BIR has issued a collection letter, final notice before seizure, warrant, garnishment, or levy;
The assessment alleges fraud, falsified documents, unreported sales, or criminal conduct;
Service was made at an old address or on a person whose authority is disputed;
The assessment covers multiple tax types or taxable years;
The amount is material to the taxpayer’s business or ability to operate;
Important accounting records are missing or held by another person;
The BIR’s authority, Letter of Authority, or assessment period appears questionable; or
The 30-day, 60-day, or 180-day period may already have expired.

Frequently asked questions

Must I pay the assessment before filing a BIR protest?

Section 228 does not make prior payment a condition for filing the administrative protest. However, interest and other consequences may continue if the assessment is ultimately sustained, and collection issues can arise later.

Can I ask for an extension of the 30-day protest period?

Do not depend on an extension. The regulations treat a failure to file a valid protest within 30 days as making the assessment final, executory, and demandable.

Is a one-page letter saying “I disagree” sufficient?

Usually not. The protest must state its nature, identify the assessment, and provide factual and legal grounds for every disputed issue. Unsupported or omitted issues may be treated as uncontested.

What if I need more time to collect evidence?

A timely request for reinvestigation permits additional evidence, but the evidence must be identified in the protest and submitted within 60 days from filing. The 30-day deadline for the protest itself remains critical.

Can I file the protest by email?

The cited BIR guidance recognizes personal filing and registered mail. Do not rely on ordinary email unless a valid BIR issuance or written case-specific instruction clearly authorizes it. Preserve proof of any authorized electronic submission.

Can I appeal directly to the CTA after receiving the PAN?

Ordinarily, no. A PAN is a proposed assessment. The usual route is to respond to the PAN, protest the later FLD/FAN administratively, and appeal the BIR’s decision or qualifying inaction.

May I wait for a decision after the 180-day period?

Yes. You may either appeal the inaction within 30 days after the 180-day period or wait for the final BIR decision and appeal within 30 days from receipt. The choices are mutually exclusive.

What if I missed the 30-day protest deadline?

The BIR will generally treat the assessment as final, executory, and demandable. Seek legal advice immediately. Questions involving invalid service, a void assessment, lack of authority, prescription, or other exceptional defects require document-specific analysis and do not guarantee relief.

Official references

This article provides general legal information, not legal or tax advice for a particular assessment. Outcomes depend on the notices, proof of receipt, audit records, tax type, taxable period, and evidence. The cited laws, procedures, and official issuances were checked as of 10 August 2026.