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 written administrative protest. The protest must be either a request for reconsideration or a request for reinvestigation, and it must properly identify and support every assessment issue you intend to dispute. Missing the 30-day deadline can make the assessment final, executory, and demandable. (Lawphil)

The deadlines change depending on the document you received:

BIR document or event	Usual deadline	What to do
Preliminary Assessment Notice (PAN)	15 days from receipt	Submit a response explaining why the proposed assessment is incorrect
FLD/FAN	30 days from receipt	File a request for reconsideration or reinvestigation
Reinvestigation protest	60 days from filing the protest	Submit all relevant supporting documents
BIR inaction on protest	180 days	Depending on the circumstances, appeal the inaction to the CTA within the next 30 days or wait for a final BIR decision
FDDA issued by the CIR's authorized representative	30 days from receipt	Appeal to the Court of Tax Appeals (CTA), or elevate the protest to the Commissioner of Internal Revenue
Final adverse decision of the CIR	30 days from receipt	File a Petition for Review with the CTA

These periods can determine whether the assessment remains contestable. Record the actual date each BIR notice was received and calculate the deadline immediately.

First determine what BIR document you actually received

Not every letter from the BIR is already the assessment that must be protested within 30 days.

Notice of Discrepancy

During an audit, the BIR may first issue a Notice of Discrepancy and conduct a discussion of the audit findings. This is generally an opportunity to explain differences, submit records, and contest proposed adjustments before a formal deficiency assessment is issued.

Treat this stage seriously. Documents and explanations submitted during the audit can later affect whether a reconsideration is sufficient or whether a reinvestigation requiring new evidence becomes necessary.

Preliminary Assessment Notice

A PAN contains the BIR's proposed deficiency assessment. Under RR No. 18-2013, it should state in detail the facts and the law, regulations, or jurisprudence on which the proposed assessment is based.

You generally have 15 days from receipt of the PAN to respond. Failure to respond allows the BIR to proceed to the FLD/FAN.

A PAN is not required in several situations specifically listed in Section 228, including certain mathematical errors apparent from a return, discrepancies between tax withheld and tax remitted, particular situations involving excess creditable withholding tax, unpaid excise tax, and transfers of articles acquired by exempt persons to non-exempt persons. In those cases, the BIR may proceed directly to an FLD/FAN. (Lawphil)

Formal Letter of Demand and Final Assessment Notice

The FLD/FAN is the critical document for the administrative protest.

Once it is received, the taxpayer generally has 30 days to file a valid written protest. Failure to do so ordinarily makes the assessment final, executory, and demandable.

Do not confuse a response to the PAN with the required protest against the FLD/FAN. Responding to the PAN does not eliminate the need to protest the subsequent FLD/FAN on time.

Check whether the assessment itself complies with due process

Section 228 requires taxpayers to be informed in writing of the law and the facts on which the assessment is made. The statute expressly provides that an assessment that fails this requirement is void. (Lawphil)

The Supreme Court reiterated this principle in 2026, explaining that a valid assessment must sufficiently disclose its factual and legal bases so the taxpayer can meaningfully contest it and present evidence. The Court also emphasized that collection of deficiency taxes normally requires a valid assessment and observance of administrative due process. (Lawphil)

Accordingly, review the entire assessment package—not merely the amount stated on the FAN. Check the FLD, assessment notices, details of discrepancies, schedules, computations, and cited legal provisions.

Possible issues to investigate include:

whether the BIR clearly identified the transactions or adjustments producing the alleged deficiency;
whether the computations can be reconciled with the taxpayer's returns and books;
whether the assessment explains why claimed expenses, credits, exemptions, or deductions were rejected;
whether the correct tax law and taxable period were applied;
whether required notices were properly issued and served;
whether the audit and assessment were performed by properly authorized revenue officers;
whether the assessment was issued within the applicable prescriptive period; and
whether collection action is being attempted without a valid assessment.

Not every procedural irregularity automatically voids an assessment. Prescription, authorization, service, and due-process defenses can turn on the exact documents and dates, so they should be evaluated from the complete audit record.

Choose between reconsideration and reinvestigation

The protest must specify which remedy you are requesting.

Request for reconsideration

A request for reconsideration asks the BIR to re-evaluate the assessment using the records already available and previously submitted.

This is commonly appropriate when the dispute primarily concerns matters such as:

an incorrect interpretation of law;
an erroneous computation based on existing records;
a transaction already documented during the audit;
incorrect characterization of income or expense; or
a legal or factual conclusion that can be resolved from documents already in the BIR's possession.

The special 60-day deadline for submitting supporting documents does not apply to a request for reconsideration under RR No. 18-2013.

Request for reinvestigation

A request for reinvestigation asks for a re-evaluation based on newly discovered or additional evidence that the taxpayer intends to present.

The protest should identify that additional evidence. All relevant supporting documents must then be submitted within 60 days from the filing of the protest.

This deadline is important. The regulations provide consequences for failure to submit the documents within the prescribed period.

The Supreme Court has also looked beyond labels when determining the real nature of a protest. In Commissioner of Internal Revenue v. Maxicare Healthcare Corporation, the Court treated a protest indicating an intention to furnish additional supporting documents as a request for reinvestigation and recognized the taxpayer's statutory period to submit that evidence. (Lawphil)

For that reason, do not casually call a protest a "reconsideration" while simultaneously stating that important new evidence will be submitted later.

What a valid protest should contain

RR No. 18-2013 requires the written protest to state, among other matters:

the nature of the protest—reconsideration or reinvestigation;
the date of the assessment notice;
for a reinvestigation, the newly discovered or additional evidence that will be presented; and
the applicable law, rules, regulations, or jurisprudence supporting the protest.

The protest should also address the factual basis of each disputed issue.

This is not merely a drafting preference. If the FLD/FAN contains several issues and the taxpayer disputes only some of them, the assessment relating to the undisputed issues may become final, executory, and demandable. Likewise, if an issue is nominally disputed but the taxpayer fails to state its supporting factual and legal grounds, the regulations may treat that issue as undisputed.

A careful protest therefore normally identifies each assessment item separately, for example:

deficiency income tax;
deficiency VAT;
expanded withholding tax;
withholding tax on compensation;
documentary stamp tax;
disallowed expenses;
undeclared sales;
unsupported input VAT;
alleged withholding-tax deficiencies; and
applicable surcharge or interest computations.

For each item, explain what the BIR concluded, why that conclusion is wrong, the relevant facts, the applicable law, and the evidence supporting the taxpayer's position.

Where and how to file the protest

BIR guidance states that the protest against an FLD/FAN should be addressed to the Assistant Commissioner, Regional Director, or other authorized higher revenue official who issued the FLD/FAN, and filed with that official's office for recording and evaluation.

The BIR's published procedure recognizes filing:

in person; or
through registered mail.

For registered mail, the BIR states that the date of mailing shown by the post-office stamp on the envelope is considered the filing date, and the envelope becomes part of the case docket.

Do not assume that an ordinary email, private courier delivery, or submission to an unrelated BIR office will necessarily satisfy the statutory deadline unless an applicable BIR issuance or specific instruction authorizes that method.

For an in-person filing, obtain a clearly dated receiving copy. For registered mail, preserve the registry receipt, tracking records, envelope information, and proof of delivery.

Submit reinvestigation documents within 60 days

If you selected reinvestigation, calendar a second deadline immediately: 60 days from filing the protest.

The supporting documents should directly correspond to the disputed issues. Depending on the assessment, these may include:

tax returns and amended returns;
audited financial statements;
general ledgers and subsidiary ledgers;
invoices and supporting accounting records;
withholding tax certificates;
contracts and purchase orders;
bank statements and proof of payment;
reconciliations;
schedules explaining discrepancies;
corporate records;
proof of tax credits or prior payments;
correspondence with customers or suppliers; and
affidavits or other evidence explaining disputed transactions.

Organize the documents by assessment issue and identify what each document proves.

Do not simply deliver boxes of records without connecting them to the factual and legal defenses in the protest.

What happens after the protest

The BIR will review the protest and may issue a Final Decision on Disputed Assessment (FDDA).

An FDDA should state the facts and applicable law, regulations, or jurisprudence supporting the decision and indicate that it is the final decision of the Commissioner or authorized representative.

What to do next depends on who issued the adverse decision.

If the FDDA was issued by an authorized representative of the CIR

Within 30 days from receipt, the taxpayer generally has two alternatives:

appeal directly to the Court of Tax Appeals; or
elevate the protest to the Commissioner of Internal Revenue through a request for reconsideration.

At this administrative-appeal stage, RR No. 18-2013 does not allow a new request for reinvestigation. It also provides that only issues raised in the decision of the CIR's authorized representative will be entertained by the Commissioner.

If the Commissioner personally denies the protest or administrative appeal

The remedy is generally an appeal to the CTA within 30 days from receipt of the Commissioner's decision.

Do not attempt to extend that period merely by filing another motion for reconsideration with the Commissioner. RR No. 18-2013 expressly states that a motion for reconsideration of the Commissioner's denial does not toll the 30-day period to appeal to the CTA.

What if the BIR does nothing for 180 days?

The 180-day rule is frequently misunderstood.

For a request for reconsideration, RR No. 18-2013 generally counts the 180-day period from the filing of the protest.

For a request for reinvestigation, it generally counts the period from the taxpayer's submission of the required supporting documents within the 60-day period.

If the BIR does not act within the applicable 180 days, the taxpayer has two mutually exclusive remedies:

appeal the BIR's inaction to the CTA within 30 days after the 180-day period expires; or
wait for the BIR's final decision, and then appeal that decision to the CTA within 30 days after receiving it. (E-Library)

The Supreme Court confirmed this rule in Lascona Land Co., Inc. v. Commissioner of Internal Revenue. A taxpayer is not automatically required to appeal merely because 180 days have elapsed. The taxpayer may deliberately await the BIR's final decision. However, the two remedies are mutually exclusive: once the taxpayer chooses one, the other is no longer available. (E-Library)

This makes the 180-day date strategically important. Calculate it carefully rather than simply waiting indefinitely without knowing which remedy is being preserved.

Appealing to the Court of Tax Appeals

Disputed BIR assessments fall within the appellate jurisdiction of the Court of Tax Appeals in Division. The taxpayer ordinarily seeks review by filing a Petition for Review. (Lawphil)

The statutory 30-day appeal deadline should be treated as critical. The petition must also comply with the current CTA Rules regarding pleadings, attachments, docket fees, service, and other filing requirements.

An appeal to the CTA does not automatically stop tax collection. Republic Act No. 1125, as amended by RA No. 9282, provides that 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 when the statutory requirements are met. (Lawphil)

Accordingly, if collection measures are already threatened or underway, the taxpayer should not assume that merely filing the CTA case is enough to stop them.

Evidence you should preserve immediately

As soon as an assessment dispute begins, preserve a complete chronological file containing:

the Letter of Authority or electronic Letter of Authority;
Notice of Discrepancy and related correspondence;
PAN and all attachments;
proof of the exact date the PAN was received;
the taxpayer's PAN response and proof of filing;
FLD/FAN and all schedules and Details of Discrepancies;
proof of the exact date the FLD/FAN was received;
the protest letter and stamped receiving copy or postal records;
all documents submitted during reinvestigation;
proof of the date those documents were submitted;
FDDA and proof of receipt;
administrative appeal to the CIR, if any;
subsequent BIR decisions and collection notices;
returns, books, invoices, contracts, bank records, and reconciliations supporting the disputed transactions; and
emails, letters, meeting notes, and transmittal sheets showing what was given to the BIR and when.

The dates of receipt and filing can be just as important as the merits of the tax computation.

Common mistakes that can seriously damage a protest

Missing the 30-day FLD/FAN deadline. Once the assessment becomes final, ordinary reconsideration or reinvestigation is no longer available.

Treating the PAN response as the final protest. The FLD/FAN must still be timely protested.

Using a vague protest letter. A statement that the taxpayer "disagrees with the assessment" without properly stating the factual and legal grounds can leave issues undisputed.

Challenging only the total amount instead of every assessment item. Uncontested issues may become final even while other issues remain disputed.

Choosing reconsideration while intending to introduce substantial new evidence. The substance of the request matters, not merely the caption.

Choosing reinvestigation and then missing the 60-day document deadline.

Sending the protest to the wrong BIR office. Follow the BIR rule directing the protest to the official who issued the assessment and file it with the proper office. (Bir Cdn)

Assuming another request for reconsideration to the CIR stops the CTA deadline. It does not when the Commissioner has already denied the protest or administrative appeal.

Assuming a CTA appeal automatically freezes collection. It generally does not. (Lawphil)

When legal or tax assistance becomes urgent

Prompt professional review is especially important when:

fewer than 30 days remain before the protest or CTA deadline;
the assessment involves a substantial amount;
the BIR has issued an FDDA;
a Warrant of Distraint and/or Levy, garnishment, or other collection measure has been issued or threatened;
the taxpayer disputes whether a notice was properly served;
there may be an issue involving prescription;
the validity or authority of the audit itself is questioned;
the assessment alleges fraud or circumstances that could lead to criminal exposure;
the case involves complicated transfer pricing, withholding, VAT, tax treaty, related-party, or cross-border issues;
important documents were not previously submitted and reinvestigation may be necessary; or
the 180-day BIR inaction period is about to expire.

Tax assessment cases can be lost through procedural default even where the underlying tax position is defensible.

Frequently asked questions

Do I have to pay the assessment before filing a protest?

Section 228 provides an administrative mechanism for disputing an FLD/FAN and does not make prior payment a prerequisite to filing the protest. Once an assessment becomes final, however, the BIR may pursue collection through remedies authorized by law.

How many days do I have to protest a BIR assessment?

A valid administrative protest against an FLD/FAN generally must be filed within 30 days from receipt. (Lawphil)

How long do I have to answer a PAN?

Generally 15 days from receipt under RR No. 18-2013.

What is the difference between reconsideration and reinvestigation?

Reconsideration relies on the existing record. Reinvestigation relies on newly discovered or additional evidence that the taxpayer intends to submit.

Does the 60-day supporting-document deadline apply to every protest?

No. Under RR No. 18-2013, the 60-day deadline applies to a request for reinvestigation, not to a request for reconsideration.

What happens if only some assessment issues are protested?

The portions that are not properly disputed can become final, executory, and demandable even while the other issues remain contested.

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

You may generally either appeal the inaction to the CTA within the following 30 days or wait for the BIR's final decision and appeal that decision within 30 days from receipt. These remedies are mutually exclusive. (E-Library)

Can I appeal an FDDA to the Commissioner instead of immediately going to the CTA?

If the adverse FDDA was issued by the Commissioner's duly authorized representative, RR No. 18-2013 generally permits either a CTA appeal or an administrative appeal by reconsideration to the CIR within 30 days. If the Commissioner has already issued the adverse final decision, the next remedy is generally the CTA.

Does filing with the CTA stop BIR collection?

Not automatically. The CTA has statutory authority to suspend collection in appropriate circumstances, but the taxpayer must seek the appropriate relief. (Lawphil)

Official sources

National Internal Revenue Code, Section 228 on protesting assessments: Republic Act No. 8424 on Lawphil
BIR Revenue Regulations No. 18-2013, amending the assessment and protest rules under RR No. 12-99: BIR Revenue Regulations No. 18-2013
BIR guidance on responding to deficiency assessments and filing administrative protests: BIR RMC No. 15-2020 Annex A
BIR clarification on where protests should be filed: BIR RMC No. 11-2014
Revised Rules of the Court of Tax Appeals: Court of Tax Appeals Rules
Republic Act No. 9282, expanding CTA jurisdiction and governing the effect of CTA appeals: Republic Act No. 9282 on Lawphil
Supreme Court decision on the two remedies following 180 days of BIR inaction: Lascona Land Co., Inc. v. Commissioner of Internal Revenue
Supreme Court decision reaffirming the need for factual and legal bases in tax assessments: CIR v. Elric Auxiliary Services Corporation/Sacred Heart Gas Station

This article provides general legal information about Philippine BIR deficiency-tax assessments and is not a substitute for advice based on the taxpayer's actual notices, tax records, dates of receipt, and audit history. Assessment remedies are highly deadline-sensitive. Laws, regulations, jurisprudence, and official BIR procedures were checked through August 25, 2026.