How to Prepare for FIRS Audit in Nigeria: A Comprehensive Guide

An audit letter from FIRS arrives. Your stomach drops.

What do they want? Did you make a mistake? How bad will the penalties be?

Here is the truth. Audits are stressful. But they do not have to be disastrous.

Proper preparation makes all the difference. Good records. Clean filings. Knowing your rights.

The tax landscape just changed dramatically. FIRS is now the Nigeria Revenue Service as of January 2026. E-invoicing is mandatory. The rules are stricter.

Let me walk you through exactly how to prepare for a tax audit in Nigeria.

What is a tax audit?

Definition: According to the Tax Foundation, a tax audit is “a formal investigation of financial information to verify an individual or corporation has accurately reported and paid their taxes.”

Here is the simple version.

The tax authority checks your books. They verify you paid what you owe. They look for errors, omissions, or fraud.

Audits verify the accuracy of financial records. They detect potential errors or fraud. They ensure compliance with tax laws. They help close the gap between what is owed and what is actually paid.

Access our tax advisory services to ensure your business is audit-ready.

FIRS to Nigeria Revenue Service: what changed in January 2026

President Bola Ahmed Tinubu signed sweeping tax reforms. The Federal Inland Revenue Service officially became the Nigeria Revenue Service on January 1, 2026.

This is not just a name change.

The NRS now oversees all federal government revenue, including both tax and non-tax sources. The mandate is much broader.

Enhanced digital compliance. The NRS is deploying a single window for tax administration. E-invoicing and automated audits are coming. Harassment and corruption are being eliminated.

Harmonised identification. Your Tax Identification Number is now mandatory for financial transactions. Your NIN serves as your Tax ID. This creates a comprehensive tracking system.

Improved transparency. The Office of the Tax Ombud provides an impartial arbiter for taxpayer complaints. Businesses now have a clearer path for resolving disputes.

E-invoicing mandate: what you must know

This is one of the biggest changes affecting audit preparation.

Medium and small VAT-registered businesses must comply from January 1, 2026. Large taxpayers started in November 2025.

Technical requirements are specific.

Invoice formats must be XML or JSON following the UBL 3.0 standard. You need 55 mandatory data fields across eight categories. Digital signatures use the ECDSA algorithm. OAuth 2.0 authentication and TLS 1.3 encryption are required. RESTful API connections to FIRSMBS are mandatory.

Reporting obligations are strict.

For B2C transactions exceeding ₦50,000, you must report invoice details to FIRSMBS within 24 hours of issuance. Near real-time reporting ensures high-value transactions are captured promptly.

Businesses with properly implemented e-invoicing systems will have organised, verifiable transaction records. This significantly streamlines the audit process.

Our digital compliance advisory can help you implement compliant e-invoicing systems.

Tax relief and new exemptions under the 2025 reforms

The reforms bring stricter compliance requirements. But they also introduce relief measures.

Individuals earning ₦800,000 or less annually are now completely exempt from personal income tax. Taxpayers can claim a 20% deduction on annual rent for the first time.

These exemptions are critical for audit preparation. They are legitimate deductions. You must document them properly. Understanding which exemptions apply ensures you neither overpay nor underreport.

Essential steps for FIRS audit preparation

Successfully navigating a tax audit requires systematic preparation.

Step one: Maintain comprehensive financial records

Every invoice, receipt, and payment record should be properly filed and easily accessible. Regular bank reconciliation between your books and statements demonstrates financial accuracy. Keep detailed payroll records, including PAYE calculations and remittances. Maintain asset registers with depreciation schedules and disposal records. Keep copies of all filed returns with proof of payment.

With the transition to digital systems, consider cloud-based accounting software. It provides audit trails and easy retrieval of historical data.

Step two: Ensure e-invoicing compliance

Integrate your accounting systems with FIRSMBS or use certified Access Point Providers. Ensure all invoices contain the required 55 mandatory fields. Maintain digital certificates for API authentication. Keep records of CSID and IRN for all transactions. Document any rejected invoices and their corrections.

Non-compliance with e-invoicing requirements will trigger closer scrutiny during audits.

Step three: Verify Tax Identification Numbers

Ensure all employees have valid TINs linked to their NINs. Maintain updated TIN records for all vendors and contractors. Verify customer TINs for significant B2B transactions. Regularly update your company’s TIN registration information.

Step four: Conduct internal audit reviews

Before facing an external audit, do your own review. Reconcile all tax returns with financial statements. Identify and correct discrepancies in reported income or expenses. Review expense classifications to ensure proper deduction claims. Verify VAT calculations and remittances. Check compliance with withholding tax obligations.

Step five: Organise documentation by tax type

For Company Income Tax, keep financial statements, profit and loss accounts, tax computations, and evidence of estimated tax payments. For VAT, maintain input and output VAT registers, VAT returns, and evidence of remittances. For Withholding Tax, keep deduction schedules, remittance evidence, and WHT credit notes. For PAYE, maintain monthly schedules, annual returns, and employee tax cards.

Step six: Update knowledge of tax law changes

The 2025 tax reforms introduced numerous changes. Stay informed about new exemption thresholds. Understand the consolidated tax framework replacing over 60 disparate taxes. Know the current CIT rate and sector-specific provisions. Be aware of the new 4% Development Levy on assessable profits for companies (excluding small businesses).

Step seven: Prepare your audit team

Designate specific personnel responsible for audit coordination. Identify internal staff who understand your accounting systems and tax positions. Brief team members on proper communication protocols with auditors. Ensure relevant personnel are available during the audit period. Consider engaging external tax consultants for complex matters.

Our audit and assurance services can help you prepare for and navigate the audit process.

Common audit triggers and how to avoid them

Understanding what attracts audit attention helps you proactively address red flags.

Significant variances in reported income. Large fluctuations in year-over-year revenue without a clear business justification trigger scrutiny. Maintain documentation explaining significant changes in business performance.

Disproportionate expense claims. When expenses appear unusually high relative to income, especially in categories like entertainment, travel, or professional fees, auditors notice. Ensure all expense claims are properly substantiated with receipts and business justification.

Inconsistent information across returns. Discrepancies between company tax returns and VAT returns or WHT schedules raise red flags. Regular internal reconciliation prevents these inconsistencies.

Repeated late filings or non-compliance. A history of late submissions or previous compliance issues increases your audit risk profile. Establish systems for timely filing.

Industry-specific red flags. Certain industries face higher scrutiny due to their cash-intensive nature or complex transactions. Retail, construction, real estate, and professional services need exceptionally detailed records.

E-invoicing non-compliance. With new digital requirements, failure to properly implement e-invoicing or repeated validation errors will attract immediate attention.

What to expect during a tax audit

Understanding the audit process reduces anxiety.

Types of tax audits in Nigeria

Desk audits are conducted at the tax authority’s office. They typically involve reviewing specific documents or clarifying particular issues. Communication happens primarily through correspondence.

Field audits involve auditors visiting your business premises. They examine records in person. These are more comprehensive and may involve interviews, physical asset inspection, and a detailed review of your accounting systems.

Issue-specific audits focus on particular aspects of your tax return. Transfer pricing arrangements, large expense claims, or specific deductions.

The audit timeline

Notification. You will receive an official letter from NRS specifying the tax types and periods under review, required documents, and initial meeting dates.

Opening conference. Auditors introduce themselves, explain the audit scope, outline required documentation, and establish timelines.

Fieldwork. Auditors examine your financial records, accounting systems, and supporting documentation. This phase may involve multiple requests for additional information.

Site visit (if applicable). For field audits, auditors may observe business operations, interview staff, and verify physical assets against records.

Preliminary findings. Before finalising their report, auditors typically discuss preliminary findings. This allows you to provide explanations or additional evidence.

Final report. The formal audit report outlines findings, any additional taxes assessed, penalties, and interest charges.

Resolution. You have the right to accept findings, provide additional information, or file an appeal.

Your rights and responsibilities during an audit

The Office of the Tax Ombud provides an impartial arbiter for taxpayer complaints. Know your rights.

Your rights include:

• Professional treatment. You have the right to courteous, professional treatment throughout the process.

• Representation. You may be represented by qualified tax professionals, accountants, or legal counsel during all audit proceedings.

• Clear explanation. Auditors must clearly explain the purpose of the audit, what documents are needed, and the basis for any proposed adjustments.

• Privacy. Your tax information must be kept confidential and used only for legitimate tax administration purposes.

• Appeal. If you disagree with audit findings, you have the right to appeal to the Tax Appeal Tribunal or pursue other dispute resolution mechanisms.

• Reasonable timeframes. While you must cooperate promptly, you can request reasonable extensions when gathering complex documentation.

Your responsibilities include:

• Cooperation. Provide requested documents within specified timeframes. Respond to auditor inquiries truthfully.

• Access. Allow auditors reasonable access to your premises during normal business hours for field audits.

• Accuracy. Ensure all information and documentation provided is accurate and complete.

• Record retention. Maintain tax records for the legally required period of generally six years in Nigeria.

At Stonehill Research , we help clients navigate audits while protecting their rights.

Post audit: responding to findings

How you respond to audit findings significantly impacts the outcome.

Possible audit outcomes

No change means the audit confirmed your tax returns were accurate. No adjustments are necessary.

An agreed assessment means you accept the auditor’s findings. You pay any additional taxes, penalties, and interest assessed.

Partial agreement means you agree with some findings but dispute others. This leads to partial payment and appeals on contested items.

Full disagreement means you contest all findings. You pursue formal dispute resolution.

Steps to take after receiving audit findings

Analyse thoroughly. Understand the basis for adjustments. Verify calculations are correct.

Seek professional advice. Before responding, seek advice from qualified tax consultants. They can evaluate whether findings are reasonable and advise on the best course of action.

Gather supporting evidence. If you believe findings are incorrect, compile supporting documentation that may not have been previously considered.

Respond timely. Missing response deadlines can forfeit your right to dispute findings. Adhere strictly to timeframes.

Consider settlement. In some cases, settlement negotiations with tax authorities may resolve disputes more efficiently than formal appeals.

Pursue appeals if necessary. If you genuinely believe findings are incorrect, use the appeals process. The Tax Ombudsman and Tax Appeal Tribunal provide formal mechanisms.

Learn and improve. Whether you agree with the findings or not, identify what led to the audit. Implement systems to prevent similar issues in future returns.

Key takeaways for effective audit preparation

Embrace digital transformation. Implement compliant e-invoicing systems. Maintain electronic records.

Maintain meticulous documentation. Cover all aspects of your financial and tax affairs.

Stay informed. Keep up with the 2025 tax reforms and ongoing regulatory changes.

Conduct regular internal reviews. Identify and correct issues before external audits.

Ensure TIN compliance for all business transactions and relationships.

Understand your rights under the new framework, including access to the Tax Ombudsman.

Seek professional support when facing complex tax matters or audit proceedings.

Respond promptly and professionally to all communications from tax authorities.

View audits as opportunities to strengthen your tax compliance systems.

Plan proactively rather than reactively when it comes to tax compliance.

Our capacity building services can help train your team on audit readiness.

Frequently Asked Questions

Q1: What is the definition of a tax audit according to the Tax Foundation?
A: According to the Tax Foundation, a tax audit is “a formal investigation of financial information to verify an individual or corporation has accurately reported and paid their taxes.”

Q2: What changed with FIRS in January 2026?
A: FIRS officially became the Nigeria Revenue Service (NRS) on January 1, 2026. The NRS now oversees all federal government revenue, including both tax and non-tax sources. The mandate is much broader with enhanced digital compliance requirements.

Q3: What are the e-invoicing requirements for Nigerian businesses?
A: Medium and small VAT-registered businesses must comply from January 1, 2026. Invoice formats must be XML or JSON following UBL 3.0 standard with 55 mandatory data fields. For B2C transactions exceeding ₦50,000, invoice details must be reported within 24 hours.

Q4: What are the new tax relief measures under the 2025 reforms?
A: Individuals earning ₦800,000 or less annually are now completely exempt from personal income tax. Taxpayers can claim a 20% deduction on annual rent for the first time.

Q5: What are common audit triggers in Nigeria?
A: Common triggers include significant variances in reported income, disproportionate expense claims, inconsistent information across returns, repeated late filings, industry-specific red flags (retail, construction, real estate), and e-invoicing non-compliance.

Q6: What are the types of tax audits in Nigeria?
A: The three types are desk audits (conducted at tax authority office), field audits (auditors visit business premises), and issue-specific audits (focus on particular aspects like transfer pricing or large expense claims).

Q7: How can Stonehill Research help with FIRS audit preparation?
A: Stonehill Research provides pre-audit health checks, e-invoicing implementation, documentation management, audit representation before NRS, dispute resolution through Tax Ombudsman or Tax Appeal Tribunal, tax optimisation, and training and advisory services.

Where to start tomorrow

Do not wait for an audit letter to begin preparing.

Review your e-invoicing compliance today. Are you using the correct format? Are all 55 fields populated?

Check your TIN records. Every employee. Every vendor. Every major customer.

Run an internal tax health check. Reconcile your returns to your financial statements.

Organise your documentation by tax type. Make sure you can find everything quickly.

Train your team. They need to know what to expect and how to respond.

Consider professional help. Tax compliance is complex. Good advisors pay for themselves.

The Bottom Line

Audits are stressful. But they are manageable.

The new Nigeria Revenue Service brings stricter enforcement and digital systems. E-invoicing is mandatory. The rules have changed.

But proper preparation works. Good records. Clean filings. Knowledge of your rights.

Most audits end with no adjustments or minor corrections. The businesses that struggle are those with poor records, inconsistent filings, or ignored compliance.

Do not be that business.

Get your systems right. Keep your records clean. Stay current with the rules.

And when the audit letter comes, you will be ready.

About Stonehill Research

Stonehill Research provides comprehensive tax advisory and audit preparation services to help Nigerian businesses navigate the evolving tax landscape.

Our FIRS Audit Preparation Services include:

• Pre-Audit Health Checks – Thorough reviews of your tax compliance status, identifying potential issues before they attract audit attention

• E-Invoicing Implementation – Help businesses implement compliant e-invoicing systems that meet FIRSMBS requirements

• Documentation Management – Assist in organising and maintaining proper tax documentation

• Audit Representation – Experienced tax professionals represent you before NRS

• Dispute Resolution – Guide you through the appeals process to Tax Ombudsman or Tax Appeal Tribunal

• Tax Optimisation – Structure your tax affairs to minimise liability while maintaining full compliance

• Training and Advisory – Regular updates on tax law changes and staff training

Why Choose Stonehill Research?

• Deep Local Expertise – We understand Nigeria’s tax environment and have extensive experience with FIRS and NRS procedures

• Proven Track Record – Our team has successfully represented numerous businesses through complex audits

• Proactive Approach – We prevent tax problems rather than just solving them

• Personalised Service – Every client receives tailored solutions

• Current Knowledge – We stay ahead of regulatory changes

Let’s Work Together

Don’t wait for an audit notice. Get your business audit ready now.

Contact us today:

📧 Email: info@stonehillresearch.com
📞 Phone: +234 802 320 0801
📍 Address: 5, Ishola Bello Close, Off Iyalla Street, Alausa, Ikeja, Lagos, Nigeria

Contact us today to schedule your consultation.

Stonehill Research – Your Trusted Partner in Tax Compliance and Audit Readiness.

Recommended reading from the Stonehill Research blog

• How to Register Your Business for Tax in Nigeria: A Step-by-Step Guide – Understanding the registration process before facing an audit

• Audit Exemptions for Small Companies in Nigeria: Who Qualifies in 2026? – Understanding your compliance obligations

• IFRS 16 Lease Accounting: What Nigerian Businesses Must Know – Financial reporting requirements that affect tax filings

Related services from Stonehill Research

• Tax Advisory Services – Comprehensive tax compliance and planning

• Audit and Assurance Services – Internal audit reviews and external audit support

• Digital Compliance Advisory – E-invoicing implementation and compliance

• Capacity Building – Tax compliance training for your team

• Dispute Resolution – Representation before Tax Ombudsman and Tax Appeal Tribunal

References

1. Tax Foundation. “Tax Audit Definition.”

2. Legit.ng. “Nigeria Ushers in New Revenue Era as FIRS Transforms into Nigeria Revenue Service in 2026.”

3. Global VAT Compliance. “Nigeria e-invoicing rollout: Key updates for 2026 compliance.”

4. VAT IT. “Nigeria’s E-Invoicing Mandate: What Businesses Need to Know Ahead of 2025.”

5. National Association of Local Tax Filers. “Understanding the New Tax Law: Key Changes and Implications.”

6. SeamlessHR. “Nigeria’s 2025 Tax Reform Acts: Key Tax Changes.”