Quick answer

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

Request for reconsideration if the BIR should re-evaluate the assessment using records already on file; or
Request for reinvestigation if you will present newly discovered or additional evidence.

A late, incomplete, or misfiled protest can leave the assessment final, executory, and demandable. If you choose reinvestigation, submit all relevant supporting documents within 60 days from filing the protest. If the BIR denies the protest or fails to act within the applicable 180-day period, strict rules govern an administrative appeal to the Commissioner of Internal Revenue (CIR) or a Petition for Review before the Court of Tax Appeals (CTA).

Do not wait for a collection letter before acting. The controlling rules are principally Section 228 of the National Internal Revenue Code and Revenue Regulations No. 18-2013.

Identify the notice you received

Different BIR notices require different responses.

Notice of Discrepancy

This ordinarily begins the audit discussion. Respond within the period stated in the notice and attend the scheduled discussion. Explain each discrepancy and submit supporting records, but remember that this response is not yet the formal protest under Section 228.

Preliminary Assessment Notice

A Preliminary Assessment Notice or PAN states the BIR’s proposed findings. A taxpayer who disagrees should submit a written response within 15 days from receipt.

Failure to answer the PAN allows the BIR to proceed with an FLD/FAN, but it does not eliminate the separate right to protest the eventual FLD/FAN within 30 days. A reply to a PAN is not a substitute for that protest.

The BIR may issue an FLD/FAN without first issuing a PAN only in these statutory situations:

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

Outside these exceptions, failure to issue and properly serve a required PAN may be a due-process objection.

Formal Letter of Demand and Final Assessment Notice

The FLD/FAN is the assessment that must be formally protested. The 30-day period runs from receipt, not from the date printed on the notice.

Record the exact date and circumstances of receipt immediately. Service may be made personally, through permitted substituted service, by registered or ordinary mail in the circumstances specified by the regulations, or through a reputable professional courier. Service upon an accredited tax agent appointed by the taxpayer may be treated as service upon the taxpayer.

Final Decision on a Disputed Assessment

An FDDA is the BIR’s decision on the protest. It should state the facts and legal grounds for the decision and identify itself as the final decision.

Do not assume that a document is harmless merely because it is called a “letter,” “final notice,” or “warrant.” Courts examine its contents and context. A communication that clearly rejects the protest and demands payment may affect the appeal period even if its caption is unusual.

The critical deadlines

Event	Deadline or action
Receipt of PAN	Respond within 15 days
Receipt of FLD/FAN	File a valid protest within 30 days
Filing a request for reinvestigation	Submit all relevant supporting documents within 60 days from filing
Inaction on a request for reconsideration	The 180-day period generally runs from filing the protest
Inaction on a request for reinvestigation	The 180-day period generally runs from submission of the required supporting documents within the 60-day period
Receipt of FDDA issued by the CIR’s authorized representative	Within 30 days, appeal to the CTA or elevate the matter to the CIR
Receipt of the CIR’s decision	Appeal to the CTA within 30 days
Election to appeal BIR inaction	File with the CTA within 30 days after the applicable 180-day period expires
Election to await a delayed decision	Appeal that final decision within 30 days from receipt

Treat these periods as strict. Do not assume that negotiations, follow-up letters, requests for conferences, or informal assurances extend them. File early if a deadline may fall on a non-working day or if the date or validity of service is disputed.

Choose the correct kind of protest

Request for reconsideration

Use reconsideration when the assessment can be resolved from records already submitted or already in the BIR docket. It may raise factual issues, legal issues, or both, but it does not contemplate additional evidence.

The separate 60-day document-submission period does not apply to reconsideration. Therefore, attach or identify the existing records on which the protest relies instead of assuming that new documents can be supplied later.

Request for reinvestigation

Use reinvestigation when you need to introduce newly discovered or additional evidence. The protest must:

Clearly call itself a request for reinvestigation;
Identify the additional or newly discovered evidence you intend to submit; and
Be followed by submission of all relevant supporting documents within 60 days from filing.

A vague statement that documents are still being compiled may not satisfy the regulation. If the protest does not clearly request reinvestigation, BIR procedures generally treat it as a request for reconsideration.

When documents are submitted, use a dated transmittal letter with a complete index. State that the submission contains the documents relied upon and retain proof of receipt. This helps establish when the 180-day period began.

What a valid protest should contain

Address every assessed tax, taxable period, and adjustment separately. At minimum, the protest should expressly state:

The taxpayer’s registered name, TIN, registered address, and contact details.
The assessment number, tax type, taxable period, amount, and date of the assessment notice.
The date and manner in which the FLD/FAN was received.
Whether the protest is a request for reconsideration or reinvestigation.
For reinvestigation, the newly discovered or additional evidence to be presented.
The specific facts supporting the objection to each adjustment.
The applicable statutes, regulations, and jurisprudence supporting each objection.
The computation of the amount, if any, that the taxpayer accepts and the amount disputed.
The relief requested, such as cancellation or reduction of the assessment.
The name, authority, and signature of the taxpayer or authorized representative.

If the FLD/FAN contains several issues, do not use a general statement that the entire assessment is “contrary to law.” An issue not specifically disputed and supported by facts and legal authority may be treated as undisputed. The corresponding tax may then become final and collectible.

Attach organized schedules and supporting documents. For a corporation, partnership, or representative filing, include appropriate proof of authority, such as a secretary’s certificate, board authority, special power of attorney, or tax-agent authorization, as applicable.

Where and how to file the protest

Under Revenue Memorandum Order No. 6-2023, protest letters and requests for reconsideration or reinvestigation are received by the office of the concerned Revenue Director or Assistant Commissioner–Large Taxpayers Service that signed the PAN, FAN, or FLD.

Follow the addressee and filing instructions in the assessment, but verify that the protest is delivered to the office of the CIR’s authorized representative who signed the FLD/FAN. Filing with the wrong office can make the protest ineffective.

Personal filing with a stamped receiving copy is the safest practical method. Obtain proof showing:

The complete document received;
Date and time of receipt;
Receiving office;
Name or identifying stamp of the receiving personnel; and
Number of annexes or document boxes submitted.

Do not rely solely on ordinary email unless a controlling BIR issuance or written instruction expressly authorizes that method for the particular filing. If using mail or courier after confirming it is acceptable, preserve the mailing receipt, tracking history, proof of delivery, and exact contents of the package.

Build the protest issue by issue

For each adjustment, use a consistent structure:

BIR finding

State the adjustment and amount exactly as shown in the FLD/FAN.

Taxpayer’s facts

Explain what actually occurred, referring to dates, contracts, invoices, returns, ledgers, bank records, withholding certificates, and other evidence.

Legal basis

Identify the statutory or regulatory provision and any directly applicable controlling decision. Explain how it applies to the documented facts.

Correct computation

Show the BIR computation, the disputed component, and the taxpayer’s computation. Reconcile differences rather than presenting only a bottom-line figure.

Requested action

Ask the BIR to cancel, withdraw, or reduce the specific adjustment and its related additions.

Possible objections include factual or mathematical errors, duplicate assessments, taxes already paid, incorrect classification, failure to credit withholding taxes, improper disallowance of substantiated expenses, prescription, absence or defect of the required authority to audit, improper service, omission of a required PAN, or failure of the FLD/FAN to state the factual and legal bases of the assessment. Whether any objection succeeds depends on the actual notices, authority papers, dates, and evidence.

What the BIR notices must disclose

The PAN and FLD/FAN must inform the taxpayer in writing of the facts and law on which the proposed or final assessment is based. The FDDA must likewise state its factual and legal grounds and indicate that it is the final decision.

Merely listing amounts, tax provisions, or conclusions without explaining how the BIR reached them may present a due-process issue. However, validity should be assessed from the complete notice and incorporated schedules—not from isolated wording.

The Supreme Court has emphasized both the BIR’s due-process duties and the taxpayer’s obligation to comply strictly with the form and timing of a protest. In CIR v. Maxicare Healthcare Corporation, the Court confirmed that the 60-day document period concerns a request for reinvestigation against the FLD/FAN, not a response to the PAN.

If only part of the assessment is disputed

Identify and pay the genuinely undisputed portion. Under the regulations, an adjustment that is not validly protested becomes final, executory, and demandable, and the BIR may issue a collection letter for that portion, including applicable additions.

Make clear in the payment documents and protest that payment applies only to the accepted portion. Preserve BIR Form No. 0605, bank or electronic payment confirmation, and the allocation computation.

Payment of the disputed amount is generally not a prerequisite to filing the administrative protest. Nevertheless, a protest does not necessarily stop the accrual of applicable interest or prevent all collection activity once the BIR treats an amount as final.

If the protest is denied

FDDA signed by an authorized representative

Within 30 days from receipt, choose either:

File a Petition for Review with the CTA; or
Elevate the protest to the CIR through a request for reconsideration.

An administrative appeal to the CIR is limited to reconsideration. Reinvestigation and new issues are not allowed at that stage; only issues covered by the authorized representative’s decision will be entertained.

Decision issued by the CIR

File a Petition for Review with the CTA within 30 days from receipt. A motion asking the CIR to reconsider the CIR’s own denial does not suspend or restart the 30-day CTA period.

If the BIR does not act within 180 days

The taxpayer generally has two alternatives:

Treat the inaction as a denial and file a Petition for Review with the CTA within 30 days after the applicable 180-day period expires; or
Await the BIR’s final decision and appeal within 30 days from receiving it.

These alternatives are mutually exclusive once one is pursued. The Supreme Court affirmed the option to await a delayed final decision in Light Rail Transit Authority v. BIR, but the taxpayer’s actions must remain consistent with that choice.

Calendar the 180-day and 30-day dates before deciding. The correct starting date depends on whether the filing was reconsideration, reinvestigation, or an administrative appeal to the CIR, and on when the relevant documents were submitted.

Appealing to the Court of Tax Appeals

An assessment dispute is brought to the CTA in Division through a verified Petition for Review. The petition must establish the CTA’s jurisdiction and timeliness, state the complete material facts and issues, and attach the required decision and supporting documents. Docket and other lawful fees must be paid.

The governing procedure is found in the Revised Rules of the Court of Tax Appeals. The 30-day appeal period is jurisdictional in character, so engage tax counsel well before it expires.

Current CTA filing requirements also include electronic-copy compliance. Under CTA En Banc Resolution No. 8-2024, when paper copies are filed personally, by registered mail, or through an accredited courier, the required PDF copies must be transmitted in the prescribed manner within 24 hours from filing; noncompliance can cause the pleading to be deemed not filed. Confirm the CTA’s current number-of-copies, email or electronic-transmission, formatting, payment, and service requirements immediately before filing.

An appeal does not automatically suspend tax collection. Under Republic Act No. 1125, as amended by Republic Act No. 9282, the CTA may suspend collection when the statutory conditions are met and may require a cash deposit or an acceptable surety bond of up to twice the disputed amount. A request to suspend collection requires a properly supported motion.

Evidence to preserve

Keep originals and secure searchable copies of:

Letter of Authority and any amendments or reassignment documents;
Notice of Discrepancy and conference records;
PAN, FLD/FAN, FDDA, collection letters, warrants, and attachments;
Envelopes, registry notices, courier labels, tracking records, and proofs of delivery;
Proof of the taxpayer’s registered address and registration updates;
Returns, amendments, payment confirmations, and withholding certificates;
Books, ledgers, invoices, contracts, bank records, and reconciliations;
Emails, letters, meeting minutes, and written BIR requests;
Stamped receiving copies of the protest and every supporting-document submission;
Proof of the representative’s authority;
A master chronology showing every receipt, filing, and deadline; and
Electronic copies with metadata and backups.

Do not alter originals, recreate missing acknowledgments, or backdate correspondence. If receipt is disputed, obtain affidavits promptly from the person who actually received or attempted to receive the notice.

Common mistakes

Protesting the PAN but failing to protest the FLD/FAN.
Counting 30 days from the wrong event.
Assuming discussions with the examiner extend the deadline.
Calling a filing “reinvestigation” without identifying additional evidence.
Failing to submit reinvestigation documents within 60 days.
Filing with an office other than the office of the authorized BIR signatory.
Omitting the assessment date or applicable legal authorities.
Giving one blanket objection instead of addressing every adjustment.
Leaving some tax periods or issues unprotested.
Submitting documents without an indexed receiving copy.
Filing a second request with the CIR and assuming it tolls the CTA deadline.
Missing the 30-day window after electing to appeal BIR inaction.
Filing paper copies with the CTA but missing the required electronic transmission.
Assuming a CTA appeal automatically stops distraint, levy, garnishment, or sale.

When professional help is urgent

Consult a Philippine tax lawyer promptly if:

The FLD/FAN deadline is less than ten days away;
Receipt, substituted service, or the taxpayer’s registered address is disputed;
The assessment covers several taxes or years;
Fraud, willful failure, or criminal referral is alleged;
The BIR has issued a collection letter, warrant of distraint or levy, garnishment notice, or notice of sale;
Assets or bank accounts are threatened;
The amount could materially affect payroll, operations, lending covenants, or solvency;
Prescription or validity of the Letter of Authority is an issue;
An FDDA or CIR decision has been received; or
The 180-day inaction period is about to expire.

A CPA can reconstruct computations and organize accounting evidence, but CTA litigation and legal objections should be handled by counsel familiar with tax procedure.

Frequently asked questions

Is a PAN already a final assessment?

No. It is a proposed assessment. Respond within 15 days, but separately watch for and timely protest the FLD/FAN.

Can the BIR issue an FLD/FAN without a PAN?

Only in the five situations expressly listed in Section 228. Whether an exception applies depends on the actual basis of the assessment.

Do I have to pay the whole assessment before protesting?

Generally, no. Pay the portion you genuinely do not dispute, and clearly protest the remainder. A different analysis may be necessary if collection has begun or if you seek suspension from the CTA.

Can I change reconsideration into reinvestigation later?

Do not assume so. Select the proper remedy in the original timely protest. If additional evidence is needed, expressly request reinvestigation and comply with the 60-day deadline.

Does the BIR decide which documents are relevant?

Revenue Regulations No. 18-2013 describes relevant supporting documents as those necessary to support the taxpayer’s legal and factual bases, as determined by the taxpayer. Submit a complete, organized set and explain the relevance of each item.

What happens if the protest is one day late?

The assessment may become final, executory, and demandable. Later requests generally cannot revive an assessment that has already become final.

Does an invalid protest stop the 30-day period?

No. A defective protest may be treated as void and may not toll the period. Correct any defect within the original 30-day window whenever possible.

Can I wait indefinitely after the BIR’s 180-day inaction?

The law recognizes an election to await a final decision, but that choice carries procedural risk and must be consistent with the taxpayer’s actions. Obtain advice before the 180-day period expires and preserve the calculation.

Does filing in the CTA stop collection?

No. Seek appropriate relief from the CTA if collection threatens the taxpayer or the government’s interests. Security may be required.

Official sources

This article provides general legal information, not legal or tax advice. Outcomes depend on the complete notices, records, filing history, and facts. Official sources and current procedures were checked as of August 3, 2026.