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, must identify the assessment, and must state the legal and factual grounds for disputing it. A vague letter saying only that you disagree may not be enough. If you fail to file a valid protest on time, the assessment can become final, executory, and demandable.

A request for reconsideration asks the BIR to re-evaluate the assessment using the records already submitted. A request for reinvestigation relies on newly discovered or additional evidence. If you choose reinvestigation, the supporting documents must generally be submitted within 60 days from filing the protest. The 60-day document period does not apply to a request for reconsideration.

If the BIR denies the protest, the next deadline can also be only 30 days. If the BIR does not act within the applicable 180-day period, you generally have a choice: appeal the inaction to the Court of Tax Appeals (CTA) within 30 days after the 180 days expire, or wait for the BIR's final decision and appeal that decision within 30 days from receipt. Those alternatives are mutually exclusive once one is pursued.

These deadlines are strict. The safest approach is to identify exactly what BIR document you received, record the date of actual receipt, determine the correct remedy immediately, and prepare the protest issue by issue rather than waiting until the last few days.

First identify what BIR document you received

Not every BIR audit document starts the 30-day period for protesting an assessment.

Document	What it generally means	Immediate action
Notice of Discrepancy (NOD)	Pre-assessment stage identifying audit discrepancies; it is not yet the assessment	Participate in the Discussion of Discrepancy and submit explanations and documents
Preliminary Assessment Notice (PAN)	Proposed deficiency assessment	Respond generally within 15 days from receipt
Formal Letter of Demand / Final Assessment Notice (FLD/FAN)	The assessment that must ordinarily be administratively protested	File a valid protest within 30 days from receipt
Final Decision on Disputed Assessment (FDDA)	BIR's decision on the protest	Determine the appropriate appeal immediately; a 30-day deadline commonly applies
Collection letter, warrant, levy, garnishment, or similar enforcement document	The BIR may already be treating the liability as collectible	Obtain urgent tax-law advice and verify whether an administrative or judicial deadline has already run

Under current BIR audit guidance, the NOD is part of the pre-assessment process and should expressly indicate that it is not itself an assessment. The BIR's 2026 guidance also directs revenue officers to clearly identify the factual and legal bases of unresolved discrepancies in subsequent assessment notices. (BIR)

A PAN normally gives the taxpayer 15 days from receipt to respond. But the formal administrative protest contemplated by Section 228 of the Tax Code is directed against the FLD/FAN, not merely against the PAN. The Supreme Court reaffirmed this distinction in Commissioner of Internal Revenue v. Maxicare Healthcare Corporation. (eLibrary)

There are also statutory situations in which the BIR may issue an FLD/FAN without first issuing a PAN, including specified mathematical errors appearing on the return, discrepancies between taxes withheld and remitted, certain improper carryovers of refundable withholding taxes, unpaid excise taxes, and specified transfers of articles originally acquired by exempt persons.

Therefore, the absence of a PAN does not automatically invalidate every assessment. You must determine whether the case falls within one of the exceptions.

The four deadlines you should immediately calendar

For a typical protested BIR deficiency assessment, four periods are especially important.

1. The 30-day period to protest the FLD/FAN

A written administrative protest must generally be filed within 30 days from receipt of the FLD/FAN. Failure to file a valid protest within that period ordinarily makes the assessment final, executory, and demandable.

Do not count merely from the date printed on the assessment. Preserve evidence showing when it was actually received.

2. The 60-day period for a request for reinvestigation

If the protest is a request for reinvestigation, all relevant supporting documents should be submitted within 60 days from the filing of the protest. The protest itself should specify the newly discovered or additional evidence you intend to present.

The Supreme Court has held that this 60-day opportunity forms part of the taxpayer's procedural rights when a valid request for reinvestigation has been made. In Maxicare, the premature issuance of an FDDA before the taxpayer's 60-day period had expired was held to violate due process. (eLibrary)

3. The 180-day period for BIR action

The starting point depends on the type of protest:

For a request for reconsideration, the 180 days are generally counted from the filing of the protest.
For a request for reinvestigation, the 180 days are generally counted from the submission of the required supporting documents within the 60-day period.

Record these dates separately. A mistake in identifying the start of the 180-day period can lead to a premature or late CTA appeal.

4. The 30-day CTA appeal period

An adversely affected taxpayer generally has 30 days to appeal an appealable BIR decision to the CTA. If the taxpayer elects to appeal BIR inaction after the 180-day period, the petition must generally be filed within 30 days after that period expires. (eLibrary)

The 30-day CTA period is jurisdictional in nature and should never be treated as a flexible deadline.

Step 1: Preserve proof of when you received the assessment

The date of receipt can determine whether the protest is timely.

Immediately preserve:

the FLD and every FAN attached to it;
the Details of Discrepancies or audit schedules;
the envelope in which the assessment arrived;
registry notices and registry return cards;
courier or delivery records;
email or electronic transmission records, if applicable;
the name and position of the person who received the documents;
any acknowledgment of receipt; and
a scanned copy of the complete assessment package exactly as received.

Do the same for the NOD, PAN, FDDA, and every subsequent collection notice.

Do not separate the FAN from its annexes. An assessment may involve different tax types and taxable periods, each of which must be reviewed independently.

Step 2: Check whether the assessment was procedurally valid

Before focusing exclusively on the BIR's computation, examine whether the assessment itself complied with the Tax Code and applicable BIR rules.

Did the FLD/FAN explain the factual and legal basis?

Section 228 requires the taxpayer to be informed in writing of the law and facts on which the assessment is based. RR No. 18-2013 similarly requires the FLD/FAN to state the facts and the applicable law, regulations, or jurisprudence; otherwise, the assessment may be void. (Lawphil)

Merely disagreeing with the amount is therefore not the only possible ground for protest. Examine whether the assessment sufficiently tells you:

what transaction or accounting entry is being questioned;
what taxable period is involved;
how the alleged deficiency was calculated;
what legal rule the BIR applied; and
why the BIR rejected the taxpayer's treatment.

Whether a particular notice satisfies due process depends on the actual wording and documents served, so the entire assessment package should be reviewed.

Was the audit conducted under proper authority?

For audits requiring a Letter of Authority (LOA), check who was authorized to examine the taxpayer's books and who actually performed the audit.

The Supreme Court has repeatedly treated the authority of the examining revenue officers as a serious due-process requirement. In CIR v. McDonald's Philippines Realty Corp., the Court held that substituting or replacing revenue officers without the required new or amended authority could invalidate the resulting assessment. More recent Supreme Court decisions have continued applying the LOA requirement. (Lawphil)

Preserve the original LOA or eLOA, any memorandum of assignment, reassignment papers, notices identifying the revenue officers, and documents showing who actually conducted the examination.

An LOA objection should nevertheless be based on the actual audit history. Do not assume that every personnel change automatically defeats an assessment without examining the applicable authority and records.

Was the assessment issued within the prescriptive period?

As a general rule, the BIR has three years within which to assess internal revenue taxes, subject to important statutory exceptions and rules on when the period begins. In cases involving a false return, a fraudulent return with intent to evade tax, or failure to file a return, Section 222 provides a longer period. A valid written waiver may also affect the deadline. (Lawphil)

Prescription analysis can become technical because it may depend on:

when the particular return was legally due;
when it was actually filed;
whether an amended return substantially changed the original;
whether the BIR validly invokes falsity, fraud, or non-filing;
whether waivers were executed; and
when the assessment was legally issued.

Do not raise prescription based only on the taxable year appearing on the FAN. Calculate it from the applicable statutory rules and documentary record.

Step 3: Choose between reconsideration and reinvestigation

This choice matters.

Request for reconsideration	Request for reinvestigation
Re-evaluation based on records already submitted	Re-evaluation using newly discovered or additional evidence
No statutory 60-day document-submission period under RR No. 18-2013	Supporting documents must generally be submitted within 60 days of filing the protest
180-day period generally runs from filing of protest	180-day period generally runs from submission of the required documents
Appropriate where the dispute can be resolved from the existing record and legal arguments	Appropriate where additional factual evidence must be introduced

The BIR's published procedure defines the two remedies in essentially these terms.

Do not call the protest a request for reconsideration while simultaneously stating that significant new evidence will later be submitted. Conversely, do not casually select reinvestigation if you have no additional evidence and cannot comply with the 60-day documentary period.

The substance of the letter matters, not merely its caption.

Step 4: Make the protest valid on its face

Under RR No. 18-2013, the written protest should state at least:

The nature of the protest — reconsideration or reinvestigation. If reinvestigation is requested, identify the newly discovered or additional evidence you intend to submit.
The date of the assessment notice.
The applicable law, rules, regulations, or jurisprudence supporting the protest.

A practical protest should ordinarily contain considerably more than those minimum items. Consider including:

taxpayer name, TIN, registered address, and branch code where applicable;
FLD/FAN reference numbers;
tax type and taxable period;
date of receipt;
a statement that the FLD/FAN is being timely protested;
the precise nature of the protest;
a separate heading for every disputed assessment issue;
relevant facts for each issue;
legal authorities for each issue;
computations showing the taxpayer's position;
identification of supporting documents;
the specific relief requested; and
an appropriate signature and proof of authority where a representative files for the taxpayer.

Do not rely on a one-paragraph letter saying that the assessment is "incorrect" or asking the BIR to "reconsider." The regulations expressly require substantive information, and BIR guidance warns that an invalid protest does not stop the running of the 30-day period. (BIR)

Step 5: Protest every issue you genuinely dispute

This is one of the most important rules.

If an FLD/FAN contains several issues and you dispute only some of them, the assessment attributable to the undisputed issues may become final, executory, and demandable.

The same problem can occur if you purport to protest an issue but fail to state the supporting facts and legal basis required by the regulations.

For example, if the FAN contains separate assessments involving income tax, VAT, expanded withholding tax, and withholding tax on compensation, do not simply address the issue with the largest peso amount and assume the entire FAN has been disputed.

Prepare an issue matrix such as:

Assessment issue	BIR position	Taxpayer position	Legal basis	Evidence
Issue 1	BIR adjustment	Why adjustment is disputed	Statute/regulation/case	Documents
Issue 2	BIR adjustment	Why adjustment is disputed	Statute/regulation/case	Documents
Issue 3	BIR adjustment	Why adjustment is disputed	Statute/regulation/case	Documents

This reduces the risk of accidentally allowing one component of the assessment to become final.

Step 6: File the protest with the correct BIR office

The BIR's published procedure states that the protest should be addressed to and filed with the office of the Assistant Commissioner, Regional Director, or other authorized higher revenue official that issued the FLD/FAN, as applicable.

RMC No. 15-2020 expressly recognizes filing in person or by registered mail. For registered mail, the date shown by the post-office stamp is treated as the filing date, and the envelope forms part of the case records. (BIR)

Accordingly:

If filing personally, obtain a clearly dated receiving copy.
If using registered mail, keep the registry receipt, tracking information, duplicate protest, and proof of contents.
Do not rely solely on ordinary mail.
Do not assume that sending the protest to the revenue officer who conducted the audit is equivalent to filing it with the proper office.
Do not rely solely on email unless a specific applicable BIR issuance or authorized filing procedure clearly permits it and you can establish timely filing.

When the deadline is close, filing mechanics become as important as the legal arguments.

Step 7: For reinvestigation, complete the evidence within 60 days

A request for reinvestigation is not an indefinite extension to assemble documents.

Within the 60-day period, submit the relevant evidence identified in the protest, which may include:

general ledgers and subsidiary ledgers;
invoices and supporting schedules;
withholding tax certificates;
tax returns and proof of filing or payment;
bank records;
contracts and purchase orders;
delivery documents;
importation or customs records where relevant;
payroll records;
board resolutions;
accounting reconciliations;
proof of tax credits;
correspondence explaining questioned transactions;
relevant BIR rulings or certificates; and
other documents necessary to establish the factual and legal defenses.

Prepare a formal transmittal identifying every document submitted and obtain proof of receipt.

The Supreme Court has clarified that the relevant 60-day period applies to a reinvestigation protest against the FLD/FAN, not to the earlier response to the PAN. (eLibrary)

Step 8: Track the 180-day period instead of simply waiting

Once the protest is filed and, for reinvestigation, the required documents are submitted, calculate the applicable 180-day period.

If the BIR's duly authorized representative does not act within that period, you ordinarily have two alternatives:

Appeal the inaction to the CTA within 30 days after the 180-day period expires; or
Wait for the final BIR decision and appeal that final decision within 30 days after receiving it. (eLibrary)

The Supreme Court has repeatedly recognized the second option. A taxpayer does not necessarily lose the case simply because it elects to wait for a final decision instead of immediately appealing the BIR's inaction after 180 days. (eLibrary)

The two remedies are, however, mutually exclusive. Once a taxpayer chooses to judicially appeal the inaction, it cannot simultaneously pursue the alternative of continuing to wait for an administrative decision on the same protest. (eLibrary)

This is an area where professional advice is particularly important because a mistake can deprive the CTA of jurisdiction.

What happens when the BIR issues an FDDA?

A Final Decision on Disputed Assessment should state the factual and legal basis for the decision and indicate its final character.

If the FDDA denying the protest was issued by a duly authorized representative of the Commissioner, RR No. 18-2013 generally gives the taxpayer a choice, within 30 days from receipt, to:

appeal directly to the CTA; or
elevate the matter to the Commissioner of Internal Revenue through a request for reconsideration.

At this administrative-appeal stage, RR No. 18-2013 does not allow another request for reinvestigation. The regulation also limits the matters entertained by the Commissioner to issues raised in the decision of the authorized representative.

If the Commissioner himself denies the protest or administrative appeal, the taxpayer generally has 30 days from receipt of the decision to appeal to the CTA.

Critically, filing another motion for reconsideration of the Commissioner's denial does not toll the 30-day period for appealing to the CTA.

Do not lose a CTA remedy by repeatedly asking the BIR to reconsider a decision that is already appealable.

Common substantive grounds for protesting an assessment

The proper defenses depend on the actual FAN, but common areas requiring examination include:

Incorrect factual assumptions

The BIR may have attributed transactions to the wrong taxable period, treated non-income amounts as income, duplicated transactions, used incomplete records, or misunderstood the commercial nature of a transaction.

Incorrect interpretation of tax law

The assessment may turn on the wrong tax rate, tax base, withholding classification, VAT treatment, deductibility rule, exemption, treaty provision, or timing rule.

Unsupported disallowances

Where the BIR disallows an expense, credit, or deduction, determine both whether the statutory requirements were met and whether the taxpayer possesses the required supporting documents.

Incorrect computation of penalties or interest

Check the taxpayer's applicable classification and the law in force for the relevant period. Under the Ease of Paying Taxes Act and RR No. 6-2024, qualifying micro and small taxpayers receive specified reduced civil penalties and a reduction in the interest rate imposed under Section 249. (Lawphil)

Due-process defects

Potential issues can include a deficient statement of factual or legal bases, failure to provide a legally required opportunity to respond or submit documents, or defects in the final decision.

Lack of proper audit authority

A mismatch between the revenue officers authorized by an LOA and those who actually conducted the examination can be material under Supreme Court jurisprudence. (Lawphil)

Prescription

An assessment issued after the applicable statutory period may be invalid, subject to the Tax Code's exceptions and any valid extension. (Lawphil)

These defenses should be raised only when the facts support them. A protest is stronger when each legal argument is tied directly to documents and calculations rather than presented as a generic list of alleged defects.

Do not assume every BIR procedural delay invalidates the assessment

Tax assessments are subject to procedural safeguards, but not every missed internal BIR timetable automatically nullifies an assessment.

For example, RR No. 18-2013 states that an FLD/FAN should follow after the taxpayer's response to the PAN, but BIR clarification has stated that issuance beyond the specified BIR processing period is not by itself fatal so long as the assessment is otherwise issued within the lawful period to assess. (BIR)

Focus on defects that the Tax Code, regulations, or controlling jurisprudence actually treat as material rather than assuming that every administrative irregularity voids the assessment.

Does filing a CTA case automatically stop BIR collection?

No.

As a general rule, an appeal to the CTA does not automatically suspend payment, levy, distraint, or sale of property for satisfaction of a tax liability. Section 11 of the CTA law permits the CTA, however, to suspend collection when the statutory requirements are met and collection may jeopardize the interest of the Government or the taxpayer. (Lawphil)

If the BIR is already issuing warrants, garnishing bank accounts, levying property, or taking other collection measures, merely filing a petition for review may therefore be insufficient. Counsel should immediately consider whether a motion to suspend collection or other appropriate CTA relief is necessary.

Evidence to preserve from the beginning

Keep a complete assessment file containing:

Letter of Authority or eLOA;
Notice of Discrepancy;
minutes or records of the Discussion of Discrepancy;
PAN and its attachments;
PAN response and proof of filing;
FLD/FAN and all assessment notices;
Details of Discrepancies;
envelope and proof of receipt of each BIR notice;
protest letter and receiving copy;
registry receipts and envelopes;
reinvestigation documents and transmittal letters;
all BIR correspondence;
FDDA;
collection letters and warrants;
tax returns for the affected periods;
books of accounts and accounting schedules;
invoices and withholding certificates;
contracts and transaction documents;
relevant bank records;
proof of tax payments and credits;
waivers of the statute of limitations, if any; and
a written chronology showing every receipt, filing, and deadline.

Do not discard envelopes simply because the BIR notice itself bears a date. The date of actual receipt can become decisive.

Common mistakes that can make an assessment final

Avoid these recurring errors:

Responding to the PAN but failing to protest the later FLD/FAN. A PAN response does not substitute for the required protest to the FLD/FAN. (eLibrary)
Missing the 30-day FLD/FAN protest deadline.
Filing a protest that fails to identify whether it is reconsideration or reinvestigation.
Requesting reinvestigation without identifying the additional evidence.
Failing to submit reinvestigation documents within 60 days.
Giving legal arguments for some assessment issues but saying nothing about others.
Sending the protest to the wrong BIR office.
Failing to obtain reliable proof of filing.
Assuming the BIR's silence means the assessment disappeared.
Miscomputing the 180-day period.
Waiting more than 30 days after an appealable FDDA or CIR decision.
Filing another motion with the Commissioner and assuming it suspends the CTA deadline.
Assuming a CTA appeal automatically stops collection.
Ignoring an unexpected collection letter because no document is labeled "FDDA." The legal effect of later BIR communications can depend on their language and the history of the disputed assessment, so an apparently final demand should be reviewed immediately. (Lawphil)

When legal help is urgent

Seek immediate tax counsel if:

fewer than 10 days remain in the 30-day protest or appeal period;
the assessment involves several tax types or taxable periods;
the FAN is already for a substantial amount;
fraud, falsity, or tax evasion is alleged;
the BIR claims the 10-year assessment period applies;
there is an LOA or reassignment issue;
the BIR disputes whether your protest was valid;
a 60-day reinvestigation deadline is approaching;
the 180-day BIR-action period has expired;
an FDDA has been received;
the BIR has issued a collection letter, warrant of distraint or levy, or garnishment notice;
property or bank accounts are threatened with collection; or
a CTA petition may be required.

Tax cases are unusually deadline-sensitive. A strong substantive defense can become useless if the assessment has already become final because the required protest or appeal was filed late.

FAQ

Do I have to pay the assessment before I can protest it?

For an ordinary BIR deficiency assessment under Section 228, prior payment is not generally a condition for filing the administrative protest. The taxpayer may timely dispute the FLD/FAN without first paying the full amount assessed. (Lawphil)

This should not be confused with other tax regimes that may have different payment-under-protest rules.

Can I simply protest the PAN?

You should respond to a PAN within the applicable period, but the formal administrative protest under Section 228 is directed against the FLD/FAN. If the BIR later issues an FLD/FAN, do not assume your PAN response already satisfies the 30-day protest requirement. (eLibrary)

Is the 60-day period available for every protest?

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

When does the BIR's 180-day period begin?

For reconsideration, generally from filing of the protest. For reinvestigation, generally from submission of the required documents within the allowed 60-day period. (BIR)

What if the BIR does nothing for 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. Once one route is chosen, the alternatives should not be mixed. (Lawphil)

Can I appeal an FDDA directly to the CTA?

If the adverse FDDA was issued by a duly authorized representative of the Commissioner, RR No. 18-2013 generally permits either a CTA appeal or an administrative elevation to the Commissioner through reconsideration, both subject to the applicable 30-day period. If the adverse decision is already that of the Commissioner, the remedy is generally an appeal to the CTA within 30 days.

Can I ask the Commissioner to reconsider his own denial and wait for another decision?

You may file whatever pleading is legally appropriate, but do not assume it extends the CTA deadline. 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.

Can I file the BIR protest by registered mail?

Yes. BIR's published procedure recognizes registered mail, with the post-office stamp serving as the filing date. Keep the registry receipt, envelope records, tracking information, and a complete duplicate of what was mailed. (BIR)

What if I agree with only part of the assessment?

Clearly identify what you dispute and what you do not. Under RR No. 18-2013, portions not disputed may become final, executory, and demandable even while other issues remain contested.

Does a defect in the Letter of Authority automatically cancel the tax assessment?

Not every perceived irregularity will necessarily do so, but the Supreme Court has repeatedly held that proper LOA authority is fundamental to a valid BIR examination where an LOA is required. The exact officers, dates, scope, taxable periods, and reassignment history should be examined before asserting this defense. (Lawphil)

Official sources

General-information disclaimer

This article provides general Philippine legal information and is not a substitute for advice based on the particular FLD/FAN, taxable periods, audit records, evidence, and dates in a specific case. BIR assessment and CTA appeal deadlines can become final even when substantial defenses exist, so taxpayers facing an active assessment should have the complete record reviewed promptly by a qualified Philippine tax professional or lawyer.

Sources and current procedures checked as of August 25, 2026.