Quick answer

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

Request for reconsideration — review based only on records already with the BIR; or
Request for reinvestigation — review using newly discovered or additional evidence. Submit all relevant supporting documents within 60 days from filing the protest.

These deadlines are strict. A late or defective protest can make the assessment final, executory, and demandable. If the BIR denies the protest, or fails to act within the applicable 180-day period, the taxpayer may appeal to the Court of Tax Appeals (CTA), subject to another strict 30-day deadline.

The controlling rules are principally Section 228 of the National Internal Revenue Code and Revenue Regulations No. 18-2013.

First identify what the BIR sent

Not every BIR letter is the assessment that starts the 30-day protest period.

Document	What it generally means	Immediate action
Letter of Authority or electronic Letter of Authority	Authorizes specified revenue officers to conduct an examination	Verify the officers, taxable period, tax types, and scope
Notice of Discrepancy	Communicates preliminary audit findings and opens a discussion stage	Explain the discrepancies and submit supporting documents within the period stated in the notice; under RR No. 22-2020, the discussion generally runs no longer than 30 days from receipt
Preliminary Assessment Notice (PAN)	Proposed assessment, not ordinarily the final assessment	File a detailed written reply within 15 days from receipt
FLD/FAN	Formal assessment and demand for payment	File the Section 228 protest within 30 days from receipt
Final Decision on Disputed Assessment (FDDA)	BIR decision on the administrative protest	Appeal administratively or to the CTA, as applicable, within 30 days
Collection letter, warrant of distraint or levy, or garnishment notice	Collection action or an asserted final demand	Obtain tax counsel immediately; the document’s substance and the earlier assessment history must be reviewed

A reply to a Notice of Discrepancy or PAN is useful but does not replace the formal protest required after receipt of the FLD/FAN.

The critical deadlines

Event	Deadline
Reply to PAN	Within 15 days from receipt
Protest against FLD/FAN	Within 30 days from receipt
Supporting documents for reinvestigation	Within 60 days from filing the protest
BIR action period on reconsideration	180 days from filing the protest
BIR action period on reinvestigation	180 days from submission of the required supporting documents
Appeal from denial by the Commissioner or authorized representative	Within 30 days from receipt
Appeal from BIR inaction	Within 30 days after the applicable 180-day period expires, if choosing to appeal the inaction
Administrative appeal to the Commissioner from an authorized representative’s denial	Within 30 days from receipt

Treat every period as strict. Record the actual receipt date, calculate the earliest defensible deadline, and file ahead of it. Do not assume that an informal conversation, request for an extension, motion for reconsideration, work suspension, weekend, holiday, or email exchange automatically stops or extends a statutory period.

Step 1: Preserve proof of receipt

The protest period runs from receipt, so the evidence of service may decide whether the protest is timely.

Keep:

The envelope, registry notice, courier pouch, and tracking history;
The receiving copy showing the recipient’s name, signature, designation, date, and time;
Email headers if the BIR also sent an electronic copy;
The company’s mailroom, security, or document-control log;
Any authority showing whether the recipient could accept documents for the taxpayer;
Proof of the taxpayer’s registered address and any properly reported change of address; and
The engagement or authority of any tax agent who received the notice.

Under RR No. 18-2013, BIR notices may be served personally, by substituted service, or by mail. Service on a duly appointed tax agent can be treated as service on the taxpayer. Refusing delivery is therefore dangerous and may not prevent constructive service.

Step 2: Assemble the complete assessment file

Obtain and arrange the documents chronologically:

Letter of Authority or eLA and any replacement or supplemental authority;
BIR requests for information, subpoena, and the taxpayer’s submissions;
Notice of Discrepancy, meeting minutes, position papers, and supporting schedules;
PAN and the taxpayer’s reply;
FLD/FAN, audit working-paper schedules supplied to the taxpayer, and proof of receipt;
Tax returns, amendments, payment confirmations, and withholding-tax certificates;
Audited financial statements, trial balances, general ledgers, subsidiary ledgers, and reconciliations;
Invoices, contracts, delivery documents, bank records, and third-party confirmations;
Prior BIR rulings or certificates specifically applicable to the taxpayer or transaction;
Relevant correspondence with customers, suppliers, employees, and government agencies; and
Any waiver extending the period to assess or collect, including proof of its execution and BIR acceptance.

Preserve originals. Submit legible copies unless the BIR lawfully requires original records for examination, and keep an indexed duplicate of everything filed.

Step 3: Review both the merits and the assessment process

A protest should address the BIR’s calculations and legal theory, but procedural defects can also be material. Possible issues include:

Authority to examine

Check whether the audit was conducted by revenue officers authorized through a valid LOA or eLA and whether they stayed within its taxable period and scope. The Supreme Court has held that an assessment resulting from an unauthorized examination may be void, including in Medicard Philippines, Inc. v. Commissioner of Internal Revenue and Commissioner of Internal Revenue v. Asian Agri-Business Corporation.

The BIR’s current audit framework is governed in part by Revenue Memorandum Order No. 1-2026, including its rules on electronic audit authority and the single-instance audit framework. Application of those rules depends on when and why the audit authority was issued.

PAN and opportunity to respond

A PAN is generally required, and the taxpayer ordinarily has 15 days from receipt to respond before the FLD/FAN is issued. The Supreme Court has treated this opportunity as substantive due process, not an empty formality. An FLD/FAN issued before the taxpayer receives the PAN or before the applicable reply period has been meaningfully afforded may be defective.

A PAN is not required in the five situations specified in Section 228:

A mathematical error appearing on the face of the return;
A discrepancy between tax withheld and tax actually remitted;
A taxpayer both claims a refund or tax credit for excess creditable withholding tax and carries over the same amount;
Unpaid excise tax on excisable articles; or
Transfer of an exempt person’s locally purchased or imported article to a non-exempt person.

Whether an exception applies depends on the actual basis of the assessment, not merely its label.

Written factual and legal bases

The PAN and FLD/FAN must adequately state the facts and the law, rules, regulations, or jurisprudence supporting the assessment. A bare amount or unexplained conclusion may deny the taxpayer a meaningful opportunity to respond.

The Supreme Court has repeatedly enforced this requirement, including in Commissioner of Internal Revenue v. Yumex Philippines Corporation.

Definite demand and due date

A valid final assessment should communicate the amount demanded and a definite due date for payment. The Court discussed this requirement in Commissioner of Internal Revenue v. Fitness by Design, Inc..

Prescription

The BIR generally has three years to assess, counted from the applicable statutory filing deadline or actual filing date, whichever is later. Different rules—including a ten-year period after discovery—may apply to a false or fraudulent return with intent to evade tax or to failure to file a return. Valid written waivers and other statutory grounds may also affect the calculation.

Prescription is document- and tax-type-specific. Review the filing date of every return, the assessment’s issuance and service dates, the asserted fraud or non-filing basis, and every waiver before taking a position.

Computation and applicable concessions

Recompute every tax, surcharge, interest period, credit, and payment. Under the Ease of Paying Taxes Act, qualifying micro and small taxpayers may receive reduced civil penalties and interest for covered cases. The classifications generally use annual gross sales:

Micro: below ₱3 million;
Small: ₱3 million to below ₱20 million;
Medium: ₱20 million to below ₱1 billion; and
Large: ₱1 billion or more.

The implementing rules provide a 10% civil surcharge and a reduced interest rate for covered micro and small taxpayers, subject to the applicable taxable period, violation, and classification. See Republic Act No. 11976 and Revenue Regulations No. 6-2024.

Step 4: Choose the correct type of protest

Request for reconsideration

Use reconsideration when the case can be resolved from records already submitted to or held by the BIR. Typical issues may include:

Incorrect legal interpretation;
Mathematical or transcription error;
Misapplication of a tax rate;
Failure to recognize a payment or credit already in the record; or
Conclusions contradicted by documents previously submitted.

The special 60-day period for additional supporting documents does not apply. The BIR’s 180-day action period is counted from filing the protest.

Request for reinvestigation

Use reinvestigation when newly discovered or additional evidence must be introduced. The protest must identify the evidence intended to be submitted.

All relevant supporting documents must be submitted within 60 days from filing the protest. For this kind of protest, the BIR’s 180-day action period is counted from the submission of those documents.

A request for reinvestigation that is granted can also affect the prescriptive period for collection. The choice should therefore be deliberate, not merely based on which label sounds stronger.

Step 5: Draft a valid, issue-by-issue protest

The protest should contain at least:

Taxpayer’s registered name, TIN, address, and contact details;
Date the FLD/FAN was received;
Date and identifying numbers of the assessment notices;
Tax type and taxable period for each assessment;
A clear statement that the submission is a protest under Section 228;
An express choice between reconsideration and reinvestigation;
For reinvestigation, the additional or newly discovered evidence to be presented;
Each disputed issue, amount, and computation;
Relevant facts for each issue;
Applicable statutes, regulations, and jurisprudence;
Specific objections to penalties and interest;
Procedural objections, if supported by the record;
The precise relief requested, such as cancellation or reduction;
Identification of any undisputed amount; and
A complete list of attachments.

Address every issue in the FLD/FAN. Under RR No. 18-2013, an issue not disputed with supporting facts and legal grounds may be treated as undisputed, making the amount attributable to it final, executory, and demandable.

Avoid a one-page protest that merely says the assessment is “without basis.” The Supreme Court has upheld the rejection of purported protests that omitted required particulars, as illustrated by Commissioner of Internal Revenue v. Citysuper, Inc..

Step 6: File with the correct BIR office and keep conclusive proof

File the protest with the office of the Commissioner’s duly authorized representative who signed the FLD/FAN. An administrative appeal from that representative’s decision is filed with the Office of the Commissioner.

BIR guidance directs filing by the taxpayer or duly authorized representative either personally or through registered mail with return card. See Revenue Memorandum Circular No. 39-2013 and Revenue Memorandum Circular No. 11-2014.

For personal filing, obtain a stamped receiving copy showing the date, office, recipient, and number of pages or attachments. For registered mail, preserve the registry receipt, tracking record, return card, complete duplicate, and proof of enclosure.

Do not rely solely on an email, ordinary mail, verbal handover to the revenue officer, or delivery to an office that did not issue the assessment unless a current official rule or written BIR instruction clearly authorizes that method.

If a representative files, attach appropriate proof of authority, such as a special power of attorney or corporate authorization, together with relevant tax-agent accreditation details where applicable.

Step 7: Complete a reinvestigation submission within 60 days

A request for reinvestigation should be followed by an indexed transmittal containing all relevant evidence. Organize it by assessment issue, not merely by document type.

The transmittal should:

Refer to the protest and FLD/FAN numbers;
State the protest filing date and 60-day deadline;
Identify each attachment;
Explain which finding each document addresses;
Include revised computations and reconciliations; and
State whether the submission completes the taxpayer’s relevant supporting documents.

Do not wait for the BIR to issue another request. The Supreme Court confirmed that the 60-day period runs from the protest against the FLD/FAN—not from a reply to the PAN—in Commissioner of Internal Revenue v. Maxicare Healthcare Corporation.

Step 8: Track the 180-day period

For reconsideration, count 180 days from filing the protest. For reinvestigation, count from submission of the required supporting documents.

If the BIR does not act within that period, the taxpayer has two mutually exclusive choices:

Appeal the inaction to the CTA within 30 days after the 180-day period expires; or
Continue waiting for the final BIR decision, then appeal that decision within 30 days from receipt.

Choosing to appeal the inaction bars the alternative of waiting for the BIR decision on the same protest. The Supreme Court recognized the option to wait in Lascona Land Co., Inc. v. Commissioner of Internal Revenue, while RR No. 18-2013 confirms that the two routes are mutually exclusive once one is chosen.

Calendar both the end of the 180-day period and the following 30-day CTA window. The decision whether to appeal immediately or wait should consider the strength of the evidence, continuing interest, possible collection activity, and litigation readiness.

Step 9: Respond correctly to a denial or FDDA

If the denial is issued by a duly authorized representative of the Commissioner, the taxpayer generally has 30 days from receipt to choose between:

Filing a petition for review with the CTA; or
Elevating the protest to the Commissioner through a request for reconsideration.

At this administrative-appeal stage, no reinvestigation is allowed, and the Commissioner will entertain only issues raised in the authorized representative’s decision.

If the denial is issued by the Commissioner, appeal to the CTA within 30 days. A motion asking the Commissioner to reconsider that denial does not suspend the CTA appeal period.

Do not depend entirely on the document’s title. A collection or demand letter that clearly and finally rejects the protest may be treated as the appealable decision. Obtain advice immediately whenever a post-protest letter demands payment or threatens collection.

A proper FDDA should state the facts and legal authorities supporting the decision and indicate that it is final. A defective FDDA may be challenged, but the safer course is to preserve the CTA deadline rather than assume the defect prevents the clock from running.

Appealing to the Court of Tax Appeals

CTA review is initiated by a petition for review filed with the CTA in Division. The petition must establish jurisdiction, present the complete material facts and issues, be verified, include a certification against forum shopping, attach the challenged decision, and comply with filing, service, and docket-fee requirements.

The Revised Rules of the Court of Tax Appeals govern the filing. Because a missed appeal period can deprive the CTA of jurisdiction, engage tax litigation counsel before—not after—the 30-day period is about to expire.

An appeal does not automatically stop collection. The taxpayer may ask the CTA to suspend collection when collection may jeopardize the interests of the taxpayer or the government. The CTA may require a deposit or surety bond of up to twice the amount claimed, depending on the circumstances. See Section 11 of Republic Act No. 1125, as amended and Rule 10 of the CTA Rules.

What happens while the assessment is disputed?

A timely administrative protest prevents the disputed portion from becoming final solely because no protest was filed. It does not necessarily stop interest from accruing or prevent every form of collection activity in every circumstance.

For periods beginning January 1, 2018, the ordinary interest rate under Section 249 has been implemented at 12% per year, while qualifying micro and small taxpayers may be entitled to the reduced 6% rate for covered liabilities. The correct amount depends on the tax period, taxpayer classification, payment history, and whether deficiency or delinquency interest applies. Revenue Regulations No. 21-2018 governs the general post-TRAIN interest rules.

If the taxpayer accepts part of the assessment, identify and arrange payment of the undisputed portion. Do not leave it unaddressed merely because other issues remain contested.

Settlement and compromise are different from a protest

A taxpayer may explore payment, abatement, or compromise without conceding every disputed issue, but these remedies have separate requirements and are not automatically granted.

Under Section 204 of the Tax Code, compromise may be considered where:

The assessment’s validity is doubtful; or
The taxpayer’s financial position demonstrates a clear inability to pay.

The statutory minimum is generally 10% of basic assessed tax for financial incapacity and 40% for other cases, subject to detailed regulations, evidence, payment conditions, and the required level of approval. A compromise application should not be assumed to suspend a protest or CTA deadline. Preserve the formal remedy unless authoritative written action clearly establishes otherwise.

Evidence worth preserving

Depending on the assessment, preserve:

Returns, amended returns, and electronic filing confirmations;
Authorized-agent-bank receipts and electronic payment confirmations;
Books of account, ledgers, journals, and audit trails;
Sales invoices and purchase invoices;
Withholding certificates and alphalists;
Contracts, purchase orders, delivery receipts, and acceptance records;
Bank statements and payment instructions;
Payroll, benefits, and employee records;
Inventory records and physical-count reports;
Importation, customs, and excise-tax documents;
Board resolutions, corporate approvals, and related-party agreements;
Tax treaties, residency certificates, and treaty-relief records;
BIR certificates, rulings, and registration documents;
Emails or letters explaining the commercial purpose of transactions;
Proof of every BIR submission and meeting; and
Working papers reconciling the tax return, financial statements, and BIR figures.

Do not alter, backdate, reconstruct without disclosure, or destroy records. If a document was recreated from source data, label it accurately and preserve the underlying data.

Common mistakes

Treating a PAN reply as the protest against the FLD/FAN;
Counting from the date printed on the notice instead of preserving and analyzing the receipt date;
Filing after 30 days because discussions with the revenue officer are ongoing;
Calling the protest both reconsideration and reinvestigation without making a clear choice;
Requesting reinvestigation but missing the 60-day document deadline;
Disputing only the total amount without addressing each assessment issue;
Omitting the assessment date or the applicable legal and factual grounds;
Sending the protest to the investigating revenue officer instead of the issuing office;
Failing to obtain a stamped copy, registry receipt, or return card;
Assuming a compromise offer or further motion stops the appeal clock;
Waiting beyond the 180-day period without consciously choosing between immediate CTA appeal and awaiting a decision;
Treating an FDDA or final demand as ordinary correspondence;
Assuming a CTA appeal automatically suspends collection; and
Ignoring interest and the undisputed portion while the protest is pending.

When legal help is urgent

Consult a Philippine tax lawyer immediately if:

Fewer than ten days remain before a protest or CTA deadline;
The assessment has already been received but the receipt date is uncertain;
The BIR claims fraud, falsity, non-filing, or a ten-year assessment period;
The FLD/FAN covers multiple tax types, years, or branches;
The BIR disregarded a PAN reply or issued the FLD/FAN before the reply period expired;
The audit was conducted by officers not named in the LOA or eLA;
A waiver of prescription is disputed;
The amount could threaten payroll, operations, credit facilities, or essential assets;
A collection letter, warrant of distraint or levy, garnishment order, tax lien, or seizure notice has been issued;
The BIR has referred the matter for criminal investigation; or
The 180-day period has expired and the taxpayer must choose a CTA strategy.

Frequently asked questions

Can I protest a Notice of Discrepancy?

You may and should submit a position paper and evidence, but that is an audit-discussion response. The formal Section 228 protest is filed against the FLD/FAN.

Can I protest a PAN?

You may file a written reply within 15 days. It is not the same as the 30-day administrative protest against the FLD/FAN.

Must I pay before filing the administrative protest?

There is no general prepayment requirement for a timely administrative protest. However, amounts not disputed issue by issue may become final and payable. Interest and collection risk should also be evaluated.

Which is better: reconsideration or reinvestigation?

Choose reconsideration if the existing BIR record is enough. Choose reinvestigation if additional or newly discovered evidence is necessary. The choice affects the supporting-document deadline, the 180-day reckoning date, and potentially prescription.

Can I submit supporting documents after 60 days?

For reinvestigation, relying on documents submitted after the 60-day period is unsafe. The regulations allow the BIR to deny the protest and bar the introduction of additional evidence once the period is missed.

What if the BIR asks for more documents after I submitted everything?

Respond carefully and preserve proof. State whether the requested item was already submitted, is unavailable, or is outside the assessment issue. Do not casually agree that the earlier submission was incomplete, because the completion date may affect the 180-day period.

What if the BIR does nothing for 180 days?

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. Do not drift into one option without documenting the decision and its deadlines.

Can I simply email the protest?

Do not rely solely on email unless a current official rule or case-specific written instruction expressly authorizes it. File through a recognized channel with verifiable proof.

What if my 30-day protest period has already expired?

The assessment generally becomes final, executory, and demandable. Urgent review may still be necessary to determine whether there was valid service, a valid assessment, a prohibited collection method, prescription, or another matter within the CTA’s jurisdiction. These possibilities are fact-specific and are not substitutes for a timely protest.

Can the BIR collect while the CTA case is pending?

A CTA appeal does not automatically suspend collection. The taxpayer may file a motion to suspend collection, supported by evidence, and the CTA may impose a deposit or bond condition.

Official sources

This article provides general Philippine legal information, not legal or tax advice for a particular assessment. Deadlines and remedies depend on the documents, service history, taxable period, and applicable issuances. Sources were checked as of August 3, 2026.