Quick answer

If you receive a Formal Letter of Demand and Final Assessment Notice (FLD/FAN) from the Bureau of Internal Revenue (BIR) and disagree with it, you generally have 30 days from receipt to file a valid administrative protest. The protest must identify whether you are seeking reconsideration or reinvestigation, identify the assessment being protested, and state the factual and legal grounds supporting your objections. If you miss the 30-day period, the assessment ordinarily becomes final, executory, and demandable. (E-Library)

Do not confuse the FLD/FAN with earlier audit notices. A Notice of Discrepancy (NOD) is part of the pre-assessment process and is not itself an assessment. A Preliminary Assessment Notice (PAN) normally gives the taxpayer 15 days from receipt to respond. The formal 30-day administrative protest period applies to the FLD/FAN, not to the PAN. The Supreme Court has repeatedly emphasized this distinction. (Bir Cdn)

Tax-assessment deadlines are strict. If you have received an FLD/FAN, an adverse decision on your protest, a Final Decision on Disputed Assessment (FDDA), or a collection notice while a protest is supposedly pending, determine the actual date of receipt immediately and calculate the applicable deadline before doing anything else.

Know what BIR document you received

The proper response depends on the stage of the audit.

Notice of Discrepancy

The BIR currently uses a Notice of Discrepancy during the pre-assessment stage to inform the taxpayer of discrepancies found during an audit and allow the taxpayer to explain them and submit supporting documents.

BIR Revenue Memorandum Order No. 1-2026 confirms that the NOD is not yet an assessment. It should identify the discrepancies with sufficient specificity to give the taxpayer a reasonable opportunity to explain and contest them during the Discussion of Discrepancy. (Bir Cdn)

Even though the NOD is preliminary, it should not be ignored. A well-documented response may resolve factual issues before they mature into an assessment.

Preliminary Assessment Notice

If discrepancies remain unresolved, the BIR will ordinarily issue a Preliminary Assessment Notice or PAN, unless the case falls within one of the statutory exceptions where a PAN is not required.

Under the assessment regulations, a taxpayer generally has 15 days from receipt of the PAN to respond. Failure to respond allows the BIR to proceed with the formal assessment. (Bir Cdn)

The PAN should state in detail the facts and the law, rules, regulations, or jurisprudence supporting the proposed assessment. A bare computation without enough explanation to permit an intelligent response may raise a due-process issue. (E-Library)

Formal Letter of Demand and Final Assessment Notice

The FLD/FAN is the document that must ordinarily be protested within 30 days from receipt.

It should contain a demand for payment and disclose the factual and legal bases of the assessment. Section 228 of the National Internal Revenue Code requires taxpayers to be informed in writing of the law and facts on which an assessment is made; otherwise, the assessment is void. (E-Library)

Do not wait for a collection letter, warrant, or another follow-up before protesting. The 30-day period runs from receipt of the FLD/FAN, not from the BIR's subsequent collection activity.

The 30-day protest deadline is critical

A taxpayer or authorized representative may administratively protest an FLD/FAN within 30 days from receipt.

Under Revenue Regulations No. 18-2013, failure to file a valid protest within that period ordinarily causes the assessment to become final, executory, and demandable, and a later request for reconsideration or reinvestigation will generally not revive it. (Bir Cdn)

Record the exact date of receipt. Preserve the envelope, registry information, acknowledgment receipt, electronic transmission record if applicable, and any other evidence showing when the assessment was actually received.

Do not casually assume that the date printed on the assessment is the deadline trigger. The governing period is generally based on receipt, although questions involving service or constructive service can become fact-sensitive. BIR regulations expressly recognize circumstances in which notices may be constructively served. (E-Library)

Choose between reconsideration and reinvestigation

The protest should expressly state which remedy you are requesting.

Request for reconsideration

A request for reconsideration asks the BIR to re-evaluate the assessment based on the existing records, without presenting newly discovered or additional evidence.

This is appropriate where the dispute is principally about:

an incorrect interpretation of the Tax Code;
application of the wrong tax rate or tax provision;
mathematical or computational errors apparent from existing records;
deductions or credits already substantiated in the audit record;
prescription;
lack of authority of the examining revenue officer;
defects in the assessment procedure; or
other factual or legal matters that can already be resolved from the existing record.

The special 60-day period for submission of supporting documents under Revenue Regulations No. 18-2013 applies to a request for reinvestigation, not to a request for reconsideration. (E-Library)

Request for reinvestigation

A request for reinvestigation asks the BIR to re-evaluate the assessment using newly discovered or additional evidence that the taxpayer intends to submit.

If you choose reinvestigation, the protest should identify the additional evidence you intend to present. All relevant supporting documents must generally be submitted within 60 days from filing the protest. Failure to comply can cause serious consequences for the protest. (E-Library)

The choice also has possible prescription consequences. The Tax Code and Supreme Court jurisprudence distinguish the two remedies: a request for reinvestigation that is granted by the Commissioner can suspend the applicable period for collection, while a mere request for reconsideration does not have the same effect. (E-Library)

Choose based on what the case actually requires rather than simply labeling every protest a reinvestigation.

What a valid protest should contain

Revenue Regulations No. 18-2013 requires more than a letter saying that you disagree with the assessment.

At minimum, the written protest should clearly state:

Whether it is a request for reconsideration or reinvestigation.
The date and identifying details of the assessment notice being protested.
The particular assessment issues being disputed.
The relevant facts supporting your position.
The applicable statutes, regulations, jurisprudence, or other legal authorities supporting each disputed issue.
For reinvestigation, the newly discovered or additional evidence you intend to present.
The specific relief requested, such as cancellation or reduction of particular deficiency assessments.

A protest that fails to satisfy the regulatory requirements may be treated as void and ineffective. (E-Library)

Protest every issue you actually dispute

This is one of the most important technical rules.

Suppose the FLD/FAN assesses:

deficiency income tax;
deficiency VAT;
expanded withholding tax;
documentary stamp tax; and
corresponding penalties or interest.

If your protest attacks only the VAT issue and says nothing meaningful about the others, the unprotested portions may become final, executory, and demandable.

Revenue Regulations No. 18-2013 expressly provides that where several issues are assessed but only some are disputed, the tax attributable to the undisputed issues may become final. The same problem can arise if an issue is nominally mentioned but the protest fails to state the relevant factual and legal grounds supporting the objection. (E-Library)

For a multi-issue assessment, a useful structure is therefore:

Issue 1 — Deficiency income tax

State the BIR's position, your factual objection, supporting documents, legal basis, and requested adjustment.

Issue 2 — VAT

Do the same separately.

Issue 3 — Withholding tax

Address the assessment independently rather than assuming your arguments on another tax automatically apply.

Repeat this approach for every item you intend to contest.

Check whether the assessment itself is legally valid

A protest should not focus only on accounting computations.

Tax assessments are subject to statutory and constitutional due-process requirements. Depending on the record, review issues such as:

whether the examining revenue officers were properly authorized;
whether required pre-assessment procedures were followed;
whether the PAN and FLD/FAN sufficiently disclose the factual basis of the assessment;
whether the relevant law, regulation, or jurisprudence was identified;
whether the FLD/FAN actually contains a demand for payment;
whether the assessment was issued within the applicable prescriptive period;
whether any waiver extending prescription was validly executed; and
whether the assessment involves matters outside the authorized audit.

Current BIR instructions themselves require revenue officers to observe the assessment process under Revenue Regulations No. 12-99, as amended, and require assessment notices to state their factual and legal bases. (Bir Cdn)

A table of numbers may not be enough

In Ortiz Memorial Chapel, Inc. v. Commissioner of Internal Revenue, decided on December 3, 2025, the Supreme Court declared deficiency tax assessments void where the BIR's documents contained essentially tabulated figures and generalized legal references but failed to adequately explain the factual and legal bases for the alleged deficiencies. (E-Library)

The case reinforces that taxpayers must receive enough information to understand why the BIR says additional tax is due, not merely the amount demanded.

Ortiz is especially significant because the taxpayer's administrative protest had been filed late. The Court nevertheless invalidated the assessments for lack of the factual and legal bases required by Section 228. This does not make the 30-day protest deadline optional. The general rule remains that an assessment not timely protested becomes final. A claimed void-assessment exception should not be used as a substitute for filing a timely protest whenever filing is still possible. (E-Library)

Submit and preserve the supporting evidence

Tax controversies are often decided as much by documents as by legal arguments.

Depending on the assessment, preserve and organize:

income tax, VAT, percentage-tax, withholding-tax, and other relevant returns;
audited financial statements;
trial balances and general ledgers;
sales and purchase journals;
invoices and other source documents;
contracts and purchase orders;
bank statements and reconciliations;
withholding-tax certificates;
proof of tax payments;
importation or customs documents;
payroll records;
schedules reconciling tax returns to financial statements;
correspondence with revenue officers;
the Letter of Authority and related audit notices;
NOD, PAN, FLD/FAN, FDDA, collection letters, and warrants;
proof of the dates each BIR document was received;
copies of all documents previously submitted to the BIR; and
proof showing when and how each taxpayer submission was received by the BIR.

For each BIR adjustment, create a reconciliation showing exactly how your figures differ from the BIR's figures and which documents substantiate the difference.

If original records are needed, maintain an indexed copy set and a detailed transmittal identifying every document submitted.

Obtain proof that the protest was filed on time

A strong protest that cannot be proven to have been timely filed can become useless.

Follow the filing instructions applicable to the issuing BIR office and the assessment you received. Keep reliable evidence showing:

the date of filing;
the BIR office that received it;
the identity or authority of the person filing it;
the complete protest and attachments filed; and
any BIR acknowledgment, stamped copy, official receipt record, registry record, or other official proof of receipt.

Do not rely solely on an informal conversation with the examiner.

If the deadline is approaching and the filing method stated in the assessment is unclear, verify the proper channel with the issuing BIR office promptly rather than assuming an informal email or message constitutes a valid statutory protest.

What happens after the protest

The next deadline depends partly on whether you filed a reconsideration or reinvestigation.

Request for reconsideration

For purposes of the administrative procedure under Revenue Regulations No. 18-2013, the 180-day period for action is counted from the filing of the protest in a request for reconsideration. (E-Library)

Request for reinvestigation

For a reinvestigation, the taxpayer must submit the relevant supporting documents within the applicable 60-day period, and the 180-day period is counted from the submission of the required documents as provided by the regulations. (E-Library)

Keep a written deadline calendar showing:

date FLD/FAN received;
30-day protest deadline;
date protest filed;
60-day supporting-document deadline, if applicable;
date the relevant documents were submitted;
end of the applicable 180-day period; and
any later 30-day CTA appeal period.

If the BIR denies the protest

A denial may come from the Commissioner or from a duly authorized representative.

Denial by a duly authorized representative

If the Commissioner's duly authorized representative denies the protest in whole or in part, Revenue Regulations No. 18-2013 generally permits the taxpayer, within 30 days from receipt, either to:

appeal to the Court of Tax Appeals, or
elevate the matter to the Commissioner of Internal Revenue through a request for reconsideration.

A reinvestigation is not available at this administrative-appeal stage, and the issues entertained by the Commissioner are limited in accordance with the regulation. (Bir Cdn)

Denial by the Commissioner

If the Commissioner denies the protest or administrative appeal, the taxpayer generally has 30 days from receipt of the decision to file a petition for review with the CTA.

A motion for reconsideration directed to the Commissioner after that denial does not suspend or restart the 30-day CTA period. (Bir Cdn)

This is a common and potentially fatal deadline error.

What if the BIR does nothing for 180 days?

When the applicable 180-day period expires without a decision, the taxpayer has two recognized options.

You may:

appeal the BIR's inaction to the CTA within 30 days after expiration of the 180-day period, or
wait for the BIR's final decision and then appeal that final decision to the CTA within 30 days after receiving it.

The Supreme Court has repeatedly recognized these alternatives, including in Lascona Land Co., Inc. v. Commissioner of Internal Revenue and Light Rail Transit Authority v. BIR. (E-Library)

The choices are mutually exclusive. Once a taxpayer elects the inaction route and files a CTA petition, the taxpayer cannot later switch to the option of waiting for a final BIR decision if the first CTA case was filed too late or otherwise fails. (E-Library)

This decision should therefore be made carefully.

The Final Decision on Disputed Assessment must also satisfy due process

An FDDA is not supposed to be a bare statement that the protest is denied.

BIR rules require the administrative decision on the disputed assessment to state the relevant facts and the applicable law, rules, regulations, or jurisprudence on which the decision is based, and to indicate that it is the final decision. Failure to satisfy these requirements may render the FDDA itself void. (E-Library)

A defective FDDA does not necessarily mean that every underlying assessment is automatically void. The validity of the assessment and the validity of the later administrative decision are legally distinct questions and must be analyzed separately. (E-Library)

Appealing to the Court of Tax Appeals

The CTA has exclusive appellate jurisdiction over decisions and qualifying inaction of the Commissioner involving disputed internal-revenue assessments. Republic Act No. 9282 generally requires the appeal to be brought within 30 days from receipt of the adverse decision or, when appealing qualifying inaction, from expiration of the period fixed by law. (E-Library)

CTA deadlines are jurisdictional in nature. Do not treat them like ordinary flexible administrative deadlines.

A CTA case is also substantially more formal than an administrative protest. Pleading requirements, verification, certification against forum shopping, documentary evidence, witness preparation, procedural rules, filing fees, and proof of authority to represent a corporation or other entity may all become relevant.

Does filing a CTA appeal stop BIR collection?

Not automatically.

Under Republic Act No. 9282, an appeal generally does not by itself suspend payment or BIR collection measures, including levy, distraint, or sale of property. The CTA may, however, suspend collection when the statutory conditions are met and may require the taxpayer to deposit the amount claimed or file a surety bond, subject to the limitations provided by law. (E-Library)

This becomes urgent if the taxpayer receives a:

Preliminary Collection Letter;
Final Notice Before Seizure;
Warrant of Distraint and/or Levy;
Warrant of Garnishment; or
other enforcement notice while the assessment remains disputed.

Collection action against an assessment that has not validly become delinquent can itself raise substantial legal issues. In a 2025 Supreme Court decision involving Stradcom Corporation, the Court reiterated that summary collection presupposes a valid basis for treating the tax as demandable. (E-Library)

Common mistakes when protesting a BIR assessment

Waiting for the BIR examiner to "resolve things informally"

Informal discussions do not replace a statutory protest. Once an FLD/FAN has been received, protect the 30-day deadline.

Protesting the PAN but not the FLD/FAN

A PAN response and an FLD/FAN protest are different procedural steps. A detailed PAN response does not eliminate the need to file the required protest after receiving the FLD/FAN. (E-Library)

Filing a one-paragraph objection

A protest should address every contested adjustment with facts and law. Merely saying that the assessment is "unfair," "incorrect," or "unsupported" is risky.

Failing to choose reconsideration or reinvestigation

The protest regulations expressly require the nature of the protest to be stated. (E-Library)

Choosing reinvestigation but forgetting the 60-day documents

If additional evidence is necessary, calendar the supporting-document deadline immediately.

Ignoring one of several assessed taxes

An unchallenged issue can become final even while other issues remain disputed.

Assuming another letter to the Commissioner extends the CTA deadline

Once the Commissioner has issued the relevant final denial, an additional administrative motion does not automatically toll the 30-day judicial appeal period. (Bir Cdn)

Filing at the CTA after the 180-day period without deciding which remedy you are using

If you elect to appeal BIR inaction, the petition must be filed within the applicable 30-day period. If instead you elect to wait, document that choice consistently and appeal within 30 days after receiving the eventual final decision. The two routes are mutually exclusive. (E-Library)

Ignoring defects in the assessment procedure

Do not assume that the only question is whether the BIR's arithmetic is correct. Authority, prescription, notice, service, factual basis, legal basis, and due process can determine whether an assessment is valid at all.

A practical protest workflow

Identify the document. Determine whether it is an NOD, PAN, FLD/FAN, FDDA, or collection notice.
Establish the date of receipt. Preserve objective proof.
Calendar every deadline immediately.
Obtain the complete audit file available to you. Include the LOA, notices, discrepancy schedules, prior submissions, and correspondence.
Break the assessment down by tax and issue.
Recompute the BIR figures independently.
Identify legal and procedural defenses separately from factual defenses.
Choose reconsideration or reinvestigation deliberately.
Draft a ground-by-ground protest addressing every disputed item.
Attach or identify the evidence supporting each factual assertion.
File through the proper BIR channel and preserve proof of timely receipt.
For reinvestigation, complete the documentary submission within the applicable 60-day period.
Calendar the 180-day period and determine in advance how you will handle BIR inaction.
Review every denial or FDDA immediately for a possible 30-day CTA deadline.
Take collection notices seriously even while substantive issues remain contested.

When legal or tax help is urgent

Professional assistance should be obtained promptly when:

the FLD/FAN protest deadline is near;
the assessment involves several tax types or substantial amounts;
the BIR alleges fraud or imposes a fraud-related surcharge;
the audit authority or Letter of Authority appears defective;
the assessment may already be prescribed;
the BIR relies on estimates, third-party data, unexplained bank deposits, or alleged undeclared sales;
the taxpayer needs to present substantial additional evidence;
an FDDA or other final denial has been received;
the 180-day period is expiring and a CTA strategy must be chosen;
a warrant of distraint, levy, or garnishment has been issued;
criminal tax exposure is being threatened or investigated; or
there is uncertainty about whether an assessment or BIR decision is void for lack of factual or legal basis.

Because many tax-remedy periods are jurisdictional or lead to finality, waiting until collection begins can severely narrow the available remedies.

Frequently asked questions

How many days do I have to protest an FLD/FAN?

Generally, 30 days from receipt of the FLD/FAN. (E-Library)

Do I have 30 days to answer a PAN?

No. The ordinary period to respond to a PAN is 15 days from receipt. The statutory 30-day protest applies to the FLD/FAN. (Bir Cdn)

Is a Notice of Discrepancy already a tax assessment?

No. Current BIR guidance describes the NOD as a pre-assessment document reflecting initial discrepancies, not yet an assessment. (Bir Cdn)

Do I always have to submit supporting documents within 60 days?

No. Under Revenue Regulations No. 18-2013, the specific 60-day supporting-document requirement applies to a request for reinvestigation. It does not apply in the same manner to a request for reconsideration based on existing records. (E-Library)

What happens if I protest only some of the assessment?

The portions you do not validly dispute may become final, executory, and demandable. (E-Library)

What if the BIR never decides my protest?

After the applicable 180-day period, you may either appeal the inaction to the CTA within the next 30 days or wait for the final BIR decision and appeal within 30 days after receiving it. The two options are mutually exclusive. (E-Library)

Can I file another motion with the Commissioner after receiving the Commissioner's final denial to extend my CTA deadline?

Do not rely on that. Revenue Regulations No. 18-2013 states that a motion for reconsideration of the Commissioner's denial does not toll the 30-day CTA appeal period. (Bir Cdn)

Can a BIR assessment be void even if the taxpayer missed the ordinary protest deadline?

The general rule is that failure to file a timely valid protest makes the assessment final. However, the Supreme Court's December 3, 2025 decision in Ortiz Memorial Chapel demonstrates that a fundamentally void assessment—for example, one violating the mandatory requirement to disclose its factual and legal bases—can present a different legal question. This is an exceptional issue requiring careful case-specific analysis and should never be treated as permission to ignore the normal 30-day deadline. (E-Library)

Does filing an appeal automatically prevent the BIR from collecting?

No. A CTA appeal does not automatically stay collection. The CTA has statutory authority to suspend collection in appropriate circumstances, subject to conditions provided by law. (E-Library)

Official sources

General-information disclaimer

This article provides general information on Philippine tax-assessment remedies and is not a substitute for advice based on the actual FLD/FAN, audit records, proof of receipt, tax returns, supporting documents, and procedural history of a particular case. Tax-remedy deadlines can be jurisdictional or can cause an assessment to become final, so taxpayers facing an active assessment should obtain case-specific advice promptly.

Law and official sources checked: August 25, 2026.