Quick answer

If you receive a Bureau of Internal Revenue (BIR) Formal Letter of Demand and Final Assessment Notice (FLD/FAN) and disagree with it, you generally have 30 days from receipt to file a valid written administrative protest. The protest must be either a request for reconsideration or a request for reinvestigation, must identify the assessment and the legal and factual grounds for disputing it, and should expressly challenge every assessment issue you intend to contest. Failure to file a valid protest within the 30-day period generally makes the assessment final, executory, and demandable. (Lawphil)

A request for reconsideration asks the BIR to reevaluate the assessment using the existing records. A request for reinvestigation relies on newly discovered or additional evidence. For a reinvestigation, all relevant supporting documents must be submitted within 60 days from filing the protest. The 60-day document-submission period does not apply to a request for reconsideration. The Supreme Court has specifically confirmed that this 60-day period concerns a reinvestigation of the FLD/FAN—not a response to the Preliminary Assessment Notice (PAN). (Lawphil)

These deadlines are strict. A taxpayer who misses them may lose the right to challenge even an assessment that might otherwise have substantial factual or legal defects.

First determine what BIR document you received

Not every BIR letter starts the same deadline.

BIR document or event	General significance	Important period
Preliminary Assessment Notice (PAN)	Proposed deficiency assessment; ordinarily gives the taxpayer an opportunity to respond before a final assessment	15 days from receipt to respond
Formal Letter of Demand and Final Assessment Notice (FLD/FAN)	The assessment that must be administratively protested	30 days from receipt
Request for reinvestigation	Protest relying on newly discovered or additional evidence	Supporting documents within 60 days from filing the protest
BIR inaction on a reconsideration	May eventually be appealed as an inaction	Generally 180 days from filing the protest, under RR No. 18-2013
BIR inaction on a reinvestigation	May eventually be appealed as an inaction	Generally 180 days from submission of the required supporting documents
Denial or FDDA by the CIR or authorized representative	Starts an appeal period, subject to the administrative-appeal option discussed below	Generally 30 days from receipt
Inaction after the applicable 180-day period	Taxpayer may appeal the inaction to the CTA or elect to await the BIR's final decision	CTA appeal based on inaction generally within 30 days after the 180-day period

The PAN is important, but it is not the same thing as the FLD/FAN. Under RR No. 18-2013, a taxpayer generally has 15 days from receipt of the PAN to respond. If no response is filed, the taxpayer may be considered in default and the BIR may proceed to the FLD/FAN. The Supreme Court has emphasized that it is the FLD/FAN that must be administratively protested within 30 days. (Bir Cdn)

A PAN is not required in every case. Section 228 of the National Internal Revenue Code (NIRC) allows an outright FLD/FAN in specified situations, including certain mathematical errors appearing on the face of a return, discrepancies between tax withheld and tax remitted, certain double use of excess creditable withholding tax, unpaid excise taxes, and specified transfers of tax-exempt articles to non-exempt persons. (Lawphil)

Do not confuse a PAN response with the formal protest

A response to a PAN is your opportunity to persuade the BIR before the assessment becomes final in form. It can address factual errors, provide explanations, reconcile discrepancies, and raise legal objections.

But receiving or responding to a PAN does not eliminate the need to protest the later FLD/FAN.

If an FLD/FAN is subsequently served, calendar a new 30-day deadline immediately. A taxpayer who argued extensively against the PAN but fails to file a valid protest against the FLD/FAN can still end up with a final assessment. The Supreme Court has repeatedly treated compliance with the protest requirements under Section 228 and RR No. 18-2013 as essential to creating a valid disputed assessment. (Lawphil)

Choose carefully between reconsideration and reinvestigation

A request for reconsideration asks the BIR to reevaluate the assessment based on records already available. It can involve questions of law, fact, or both, but it does not contemplate the introduction of additional evidence.

A request for reinvestigation asks the BIR to reevaluate the assessment using newly discovered or additional evidence that the taxpayer intends to submit. It likewise may involve factual and legal questions. (Lawphil)

The distinction matters because the procedural consequences are different. In a reinvestigation, the taxpayer must submit all relevant supporting documents within 60 days from filing the protest. Missing that period can cause the assessment to become final for purposes of introducing the additional evidence and lead to denial of the protest.

Do not label a protest "reconsideration" merely to avoid the document deadline if the case actually depends on evidence that is not already part of the BIR record. Conversely, do not request reinvestigation unnecessarily if the dispute is purely legal and all necessary evidence is already in the file.

What a valid protest should contain

RR No. 18-2013 requires the written protest to state the nature of the protest—reconsideration or reinvestigation—the date of the assessment notice, and the applicable law, rules, regulations, or jurisprudence supporting the protest. If reinvestigation is requested, the taxpayer should identify the newly discovered or additional evidence intended to be presented. Failure to comply can make the protest void and ineffective.

A careful protest should therefore do more than say, "We disagree with the assessment."

A practical approach is to:

Identify the taxpayer and assessment precisely. State the taxpayer's name, TIN, taxable period, tax types, FLD/FAN date, assessment numbers, and date the assessment was received.
State expressly whether the filing is a request for reconsideration or reinvestigation. Do not leave the characterization ambiguous.
Challenge every disputed tax issue separately. For each item, identify what BIR assessed, explain the relevant facts, identify the legal basis for the objection, and state the relief requested.
Address the computation. Even where liability may exist in principle, check the taxable base, rates, credits, withholding taxes, prior payments, penalties, and mathematical calculations.
Raise procedural objections expressly. If applicable, identify defects involving the Letter of Authority, authority of the investigating revenue officers, service, prescription, PAN, FLD/FAN, or statement of factual and legal bases.
Identify and organize supporting evidence. For a reinvestigation, make sure all evidence on which the protest depends is submitted within the 60-day period.
Ask expressly for cancellation or reduction of the disputed assessment. Specify whether the entire assessment or only particular portions are contested.
File with the proper BIR office and preserve proof of filing. Do not rely on an informal delivery to a revenue officer without documentary proof of timely filing.

Every disputed issue should be addressed

A dangerous mistake is to protest the assessment generally while discussing only some of the individual tax findings.

RR No. 18-2013 provides that when several issues appear in an FLD/FAN and the taxpayer disputes only some of them, the assessment attributable to the undisputed issues becomes final, executory, and demandable. The same consequence may follow where an issue is nominally mentioned but the taxpayer fails to state the supporting facts and applicable law, regulations, or jurisprudence.

For example, an FLD/FAN may contain separate findings for income tax, VAT, expanded withholding tax, withholding tax on compensation, and penalties. A detailed objection to the VAT assessment does not automatically preserve objections to the other findings.

Review the FLD/FAN line by line before filing.

Check whether the assessment itself complied with due process

Section 228 requires the taxpayer to be informed in writing of both the law and the facts on which the assessment is based. An assessment that fails this requirement is void. RR No. 18-2013 similarly requires an FLD/FAN to state its factual and legal bases. (Lawphil)

The Supreme Court reaffirmed this principle as recently as 2026, explaining that a valid assessment must sufficiently inform the taxpayer of its factual and legal bases so that the taxpayer can effectively protest and present supporting evidence. (Lawphil)

That does not mean that every disagreement with the BIR's reasoning automatically creates a due-process violation. The relevant question is whether the assessment sufficiently disclosed the factual findings and legal bases necessary for the taxpayer to understand and challenge the liability being asserted.

Check the Letter of Authority if the assessment resulted from an audit

Where the assessment resulted from a BIR examination of the taxpayer's books and records, examine the Letter of Authority (LOA) and the authority of the revenue officers who actually conducted the investigation.

The Supreme Court has held that revenue officers derive their authority to conduct an examination from a valid LOA. In Commissioner of Internal Revenue v. McDonald's Philippines Realty Corp., the Court ruled that replacing the revenue officers named in an LOA without a proper new or amended authority violated due process and rendered the resulting assessment invalid. (Lawphil)

LOA issues are fact-specific. Determine who was authorized, which taxable period and taxes were covered, who actually performed the examination, and what subsequent authority—if any—was issued.

Check prescription

The ordinary rule under Section 203 of the NIRC is that internal revenue taxes must generally be assessed within three years from the statutory filing deadline or, when the return was filed late, from the actual filing date. A return filed before the statutory deadline is generally treated as filed on that deadline for purposes of computing the period. (Lawphil)

There are significant exceptions. Section 222 provides, among others, a different period in cases involving a false or fraudulent return with intent to evade tax or failure to file a return, and it permits the assessment period to be extended through a qualifying written agreement between the Commissioner and taxpayer executed before the applicable period expires. (Lawphil)

Prescription disputes can become highly technical because the relevant return, filing date, tax type, waivers, suspensions of the period, and date on which the assessment was legally made all matter. Do not conclude that an assessment is prescribed merely because the taxable year is more than three years old.

Where to file the protest

BIR Revenue Memorandum Circular No. 43-2023 reiterates that protests against an FLD/FAN are to be filed with the office of the duly authorized representative of the Commissioner who issued the FLD/FAN. (Bir Cdn)

Follow the filing instructions appearing in the assessment and applicable BIR issuances. Obtain reliable evidence showing both what was filed and when it was filed. For a physical filing, retain a complete receiving copy bearing the BIR receiving details. If another permitted mode is used, preserve the corresponding proof of transmission, delivery, and receipt.

Do not leave the only signed copy with the BIR.

What happens after you file the protest

The BIR may grant the protest, partly grant it, deny it, or fail to act within the applicable period.

A decision on a disputed assessment is normally communicated through a Final Decision on Disputed Assessment (FDDA). RR No. 18-2013 requires the decision of the Commissioner or duly authorized representative to state the relevant facts and legal authorities on which the decision is based and to state that it is the final decision. Otherwise, the decision may itself be void.

Read the signatory carefully because it affects your next remedy.

If an authorized representative denies the protest

When the protest is denied by a duly authorized representative of the Commissioner, RR No. 18-2013 generally gives the taxpayer two routes within 30 days from receipt:

The taxpayer may appeal directly to the Court of Tax Appeals, or may elevate the protest to the Commissioner of Internal Revenue through a request for reconsideration. A reinvestigation is no longer available at this administrative-appeal stage, and the Commissioner generally considers only the issues raised in the authorized representative's decision.

The Supreme Court has recognized this administrative appeal to the Commissioner as a genuine remedy. When properly and timely invoked, the authorized representative's FDDA does not become the final decision appealable to the CTA while the appeal to the Commissioner remains pending. (Lawphil)

If the Commissioner thereafter denies the protest or administrative appeal, the taxpayer generally has 30 days from receipt to appeal to the CTA. RR No. 18-2013 specifically warns that filing a motion for reconsideration of the Commissioner's denial does not suspend or restart this 30-day CTA period.

What if the BIR does nothing for 180 days?

The law protects taxpayers from waiting indefinitely.

Under RR No. 18-2013, the 180-day period is generally counted from the filing of a request for reconsideration, and from the submission of the required supporting documents in a request for reinvestigation.

When the applicable 180-day period expires without action, the taxpayer generally has two mutually exclusive choices:

The taxpayer may treat the inaction as a denial and file a petition for review with the CTA within 30 days after expiration of the 180-day period, or the taxpayer may continue waiting for the BIR's final decision and then appeal that final decision to the CTA within 30 days from receipt. The Supreme Court has repeatedly recognized these alternatives and has emphasized that exercising one excludes the other. (Lawphil)

Choosing between these remedies can materially affect jurisdiction and strategy. Once the 180-day point approaches, calculate the dates carefully and obtain tax-litigation advice before taking either route.

Appealing to the Court of Tax Appeals

The CTA has exclusive appellate jurisdiction over decisions and qualifying inaction of the Commissioner involving disputed assessments. The basic appeal period is 30 days from receipt of the appealable decision or, when the taxpayer elects to appeal an inaction, from expiration of the statutory period for BIR action. (Court of Tax Appeals)

The 30-day period is especially dangerous because an untimely petition can deprive the CTA of jurisdiction. Do not assume that ongoing communications, a collection discussion, a request for reconsideration filed after the Commissioner's final denial, or negotiations with revenue officers will preserve the CTA deadline.

Current CTA filing requirements should also be checked when the petition is prepared. The CTA has issued rules and resolutions concerning electronic copies of court submissions in addition to its Revised Rules. (Court of Tax Appeals)

BIR RMC No. 43-2023 additionally requires a taxpayer who appeals an FDDA to the Commissioner or CTA to furnish a copy of the appeal to the designated BIR office—generally the Chief of the Assessment Division for regional cases, or the concerned Head Revenue Executive Assistant for specified Large Taxpayer Service or National Investigation Division cases—within five days from filing the appeal. (Bir Cdn)

An appeal does not automatically stop BIR collection

Do not assume that filing a CTA case automatically freezes collection.

Under Republic Act No. 1125 and the CTA Rules, an appeal generally does not suspend payment, levy, distraint, or sale of property for satisfaction of the tax liability. The CTA may, however, suspend collection where the statutory requirements are met, subject to the rules governing deposits or surety bonds and jurisprudential exceptions. (Court of Tax Appeals)

Accordingly, if the BIR has issued a collection letter, final notice before seizure, warrant of distraint or levy, garnishment, or another collection measure while a dispute is pending, obtain advice immediately. The validity of collection can depend on whether the assessment had already become final and demandable, whether an administrative appeal remained pending, and whether relief from the CTA should be sought.

Evidence to preserve from the beginning

Keep the complete audit and assessment file, not merely the FLD/FAN. Important records commonly include the LOA and any later authority affecting the investigating officers; notices of discrepancy or audit correspondence; PAN and attachments; your PAN response and evidence of filing; FLD/FAN and all assessment schedules; envelopes, registry documents, courier records, receiving stamps, or other evidence showing the dates notices were actually received; the administrative protest and proof of filing; supporting documents submitted during a reinvestigation and proof of their timely submission; FDDA and proof of receipt; correspondence with the BIR; tax returns, audited financial statements, books, invoices, withholding certificates, schedules, reconciliations, contracts, bank records, and accounting workpapers relevant to the disputed findings.

Receipt dates are particularly important because a case can turn on a single missed deadline.

Common mistakes

Treating the PAN as the final assessment. The PAN normally gives an opportunity to respond, but the critical 30-day administrative protest is directed against the FLD/FAN.

Sending a vague objection. A letter that merely says the taxpayer disagrees may not satisfy RR No. 18-2013. The protest must identify its nature, assessment date, and legal grounds and should address the relevant factual grounds.

Failing to contest every issue. Portions not properly disputed may become final even while other portions remain contested.

Calling the filing a reconsideration when new evidence is necessary. The legal characterization should correspond to what the taxpayer actually intends to do.

Missing the 60-day evidence deadline in a reinvestigation. This can prevent the taxpayer from relying on additional evidence and lead to denial.

Counting on continuing discussions with the BIR. Informal negotiations ordinarily do not replace the formal remedies and deadlines established by Section 228.

Waiting after a final CIR denial because a motion for reconsideration was filed. RR No. 18-2013 expressly provides that such a motion does not toll the 30-day CTA appeal period.

Assuming a CTA appeal automatically stops collection. Suspension of collection requires separate legal consideration and, where appropriate, relief from the CTA.

When legal help is urgent

Professional assistance is especially urgent if the FLD/FAN was received close to 30 days ago; a reinvestigation's 60-day deadline is approaching; the 180-day inaction period has expired or is about to expire; an FDDA or denial from the Commissioner has been received; the assessment is substantial or involves multiple tax types; fraud or a false return is alleged; the BIR audit may have LOA defects; prescription is disputed; the BIR has issued garnishment, distraint, levy, seizure, or collection notices; or you are deciding whether to appeal immediately to the CTA or wait for a BIR decision.

The legal merits cannot rescue an otherwise valid assessment if the taxpayer allows the procedural remedy to lapse.

Frequently asked questions

Can I protest a BIR assessment without paying it first?

For the ordinary administrative protest of a deficiency assessment under Section 228, the statute provides a procedure for disputing the FLD/FAN through reconsideration or reinvestigation and does not make prior payment the condition for filing that protest. The situation changes once collection remedies and CTA proceedings become involved, so payment, collection, and suspension issues should be analyzed separately.

I replied to the PAN. Do I still need to protest the FAN?

Yes. If the BIR later issues an FLD/FAN, it should be independently protested within the applicable 30-day period. A PAN response does not substitute for the administrative protest against the FLD/FAN. (Lawphil)

Is a PAN always required?

No. Section 228 expressly identifies situations in which the BIR may issue the FLD/FAN without first issuing a PAN. (Lawphil)

Should I request reconsideration or reinvestigation?

Use reconsideration when the assessment can be resolved from the existing records. Reinvestigation is appropriate when newly discovered or additional evidence must be presented. The correct choice depends on the actual evidentiary needs of the case. (Lawphil)

How long do I have to submit documents for a reinvestigation?

Generally 60 days from filing the protest. The Supreme Court has confirmed that this period applies to a request for reinvestigation against the FLD/FAN. (Lawphil)

What happens if I do not protest within 30 days?

The assessment generally becomes final, executory, and demandable, and the BIR may proceed with collection remedies.

Can I appeal directly to the CTA after receiving the FLD/FAN?

Ordinarily, no. The assessment must first become a disputed assessment through a valid and timely administrative protest. The CTA reviews the appealable decision or qualifying inaction on that disputed assessment, not an FLD/FAN that the taxpayer simply failed to protest. (Lawphil)

What if a Regional Director or another authorized BIR representative issues the FDDA?

RR No. 18-2013 generally permits either a direct CTA appeal within 30 days or an administrative appeal to the Commissioner within 30 days. If the taxpayer timely chooses the administrative route, the case must then be resolved at the Commissioner's level before the resulting final decision is appealed, subject to the rules concerning inaction.

What if BIR does not decide my protest within 180 days?

Depending on the procedural posture, you may generally appeal the inaction to the CTA within the following 30 days or elect to wait for a final BIR decision and appeal within 30 days after receiving it. Those alternatives are mutually exclusive once one is pursued. (Lawphil)

Can the assessment be challenged because it is old?

Possibly. The ordinary assessment period is generally three years, but important exceptions, extensions, and suspension rules exist. The actual return filing date, tax type, allegations of fraud or non-filing, waivers, and other events must be reviewed before concluding that the BIR's right to assess has prescribed. (Lawphil)

Official sources

National Internal Revenue Code, particularly Sections 203, 222, and 228. Section 228 contains the core rules governing PANs, protests, document submission, BIR inaction, and CTA appeals. (Lawphil)

BIR Revenue Regulations No. 18-2013. This is the principal regulation amending RR No. 12-99 on deficiency-assessment due process, including PAN and FLD/FAN requirements, reconsideration versus reinvestigation, protest contents, 60-day submissions, FDDA procedures, and appeals. (Bir Cdn)

BIR Revenue Memorandum Circular No. 11-2014. This circular clarifies due-process and filing issues arising from RR No. 12-99 as amended by RR No. 18-2013. (Bir Cdn)

BIR Revenue Memorandum Circular No. 43-2023. This clarifies where protests and appeals concerning FLD/FANs and FDDAs are filed or furnished within the BIR. (Bir Cdn)

Revised Rules of the Court of Tax Appeals. These govern petitions for review and related CTA procedure once the administrative dispute reaches the tax court. (Court of Tax Appeals)

Supreme Court decisions on disputed assessments. Recent and controlling decisions include cases confirming the 60-day reinvestigation rule, the alternatives following BIR inaction, administrative appeals to the Commissioner, LOA requirements, and the need for a valid assessment before collection. (Lawphil)

General-information disclaimer

This article provides general Philippine legal information and is not a substitute for advice based on the taxpayer's actual FLD/FAN, audit records, proof of receipt, tax returns, supporting documents, and procedural history. Tax-assessment deadlines can be jurisdictional or otherwise result in finality, so a taxpayer facing an active assessment should have the actual documents reviewed promptly.

Law and official-source check: August 25, 2026.