How Far Back Can IRAS Go? Time Limits for Reopening Your Company’s Tax Years

For corporate income tax, IRAS generally has 4 years from the end of the Year of Assessment (YA) to raise an assessment or additional assessment, under section 74(1) of the Income Tax Act 1947. For GST, the period is 5 years from the end of the accounting period. Neither limit applies where fraud is involved, so a deliberately understated year can be reopened at any time. The same clock also limits your company: claims for relief on overpaid income tax under section 93A must be made within 4 years after the end of the YA in which the assessment was made.

Raffles Corporate Services works with a panel of experienced Singapore law firms who offer cost-effective and efficient legal service and advice. This article is general information only and is not legal advice.

How the 4-year income tax limit is counted

IRAS’s page on what happens after filing Form C-S or Form C says the statutory time limit to raise an assessment or additional assessment is 4 years, and that it does not apply where fraud is involved. For YA 2008 onwards, the 4 years run from the end of the YA, not from the end of the financial year or the date the return was filed.

Because a YA is a calendar year, the deadline always falls on 31 December. IRAS’s examples show that the financial year end does not change the result.

Applying the same rule today, November 2026, the oldest corporate tax year IRAS can still reopen in a normal case is YA 2022, which closes on 31 December 2026. From 1 January 2027, YA 2022 is time-barred unless fraud is involved, and YA 2023 becomes the oldest open year.

When there is no time limit

IRAS’s guidance on investigations by IRAS states that where there is fraud, the statutory limitation in section 74(1) of the Income Tax Act and section 45(5) of the GST Act does not apply. The Act’s wording also refers to wilful default, so a deliberate failure, not just outright fraud, may keep a year open.

The limit is a protection for honest mistakes, not for concealed income. The penalties in fraud cases are heavy: IRAS says serious fraudulent evasion can attract a penalty of up to four times the tax undercharged, plus a fine and imprisonment. If an old error may have been deliberate, get advice before you contact IRAS. Our article on IRAS’s Voluntary Disclosure Programme explains how disclosure affects the outcome.

How far back can IRAS go for GST?

For GST, IRAS refers to a 5-year period from the end of the prescribed accounting period, for periods ending on or after 1 January 2007, with no limit in fraud cases. The same 5 years apply in the other direction. IRAS’s page on correcting errors in a GST return says errors must be corrected within 5 years from the end of the relevant accounting period, for example by 31 December 2028 for a period ending 31 December 2023. A refund of overpaid GST must also be claimed within 5 years, and IRAS treats a claim as valid only when the errors for all affected periods are fully quantified.

The time limits at a glance

Your company found an old mistake: what now?

The direction of the error decides the route.

The company paid too much tax

If a mistake in the company’s own return led to too much tax, for example a missed deduction or capital allowance, IRAS says the company may apply in writing for relief for error or mistake. The deadline is no later than 4 years after the end of the YA in which the assessment was made. IRAS’s example is an error in the YA 2021 return assessed in 2022, which can be claimed until 31 December 2026. Miss the window and the overpaid tax generally stays with IRAS.

The company paid too little tax

If the mistake meant too little tax, the right route is a voluntary disclosure, not waiting to see whether the year becomes time-barred. Under IRAS’s Voluntary Disclosure Programme, a qualifying disclosure made within one year of the statutory filing deadline attracts no penalty. After that grace period, the reduced penalty for corporate tax is 5% of the tax undercharged for each year the error went uncorrected. To qualify, the disclosure must be self-initiated, made before IRAS raises a query or starts an audit, accurate and complete, and the company must cooperate and pay or arrange to pay. If IRAS has already written to you, read our guide to the voluntary disclosure opportunity letter.

The error touches years that are already closed

Work out each affected YA separately. Some years may be inside the 4-year window and some outside. Do not assume an old year is closed if the error may have been deliberate, and do not use the time limit as a reason to leave out years from a disclosure that IRAS could still assess.

Steps when an old error comes to light

1. Preserve the evidence. Keep the original ledgers, computations and filed returns before anyone corrects the books.
2. Identify each affected year. List the financial year, YA and, for GST, the accounting periods.
3. Quantify the tax effect for each year. Separate errors that increase tax from those that reduce it.
4. Check each year against the limits. Use the table above for IRAS’s window, your section 93A window and the GST 5-year window.
5. Decide the route. Section 93A relief for overpayments, voluntary disclosure for underpayments, GST F7 for GST errors.
6. File before the earliest deadline. A section 93A claim for an older YA may expire on 31 December of this year.
7. Fix the cause. Update the chart of accounts, controls or tax computation template so the error does not repeat.

Example: a missed capital allowance claim

Example: In November 2026, a new finance manager at a logistics company discovers that equipment bought in the financial year ended 31 December 2021 was expensed in the accounts but never claimed for capital allowances. The YA 2022 return was assessed in 2022.

The company paid too much tax, so the route is a section 93A claim. On IRAS’s rule, the 4 years run from the end of YA 2022, so the application must be made in writing by 31 December 2026, a matter of weeks away. The manager also finds that a supplier rebate in YA 2023 was never recorded as income. That year is still open to IRAS until 31 December 2027, so the company prepares a voluntary disclosure for it at the same time rather than offsetting the two errors informally.

How long should records be kept?

IRAS’s record-keeping requirements say companies must keep source documents, accounting records, bank statements and other transaction records for at least 5 years from the relevant YA. A company that is struck off or wound up must still have its records kept for 5 years after dissolution, by a former officer or the liquidator. GST records must also be kept for at least 5 years; see our guide to GST record-keeping.

The 5-year record period is longer than the 4-year income tax limit for a reason: it leaves the evidence available for the full assessment window. Where fraud could be alleged, IRAS is not bound by the limit at all, so records that prove a position was honest are worth keeping longer.

Frequently asked questions

Does the 4-year limit start when we file Form C-S?

No. It runs from the end of the YA. A YA 2023 assessment can be raised until 31 December 2027, whatever the filing date.

If IRAS audits us, can it look at years beyond 4 years?

Not to raise an assessment in a normal case. Where fraud is involved the limit does not apply. See our guide to preparing for an IRAS tax audit.

Can we still object to a Notice of Assessment from two years ago?

The objection window is 2 months from the notice date, and IRAS says the assessment becomes final if no objection is filed. If the problem was your company’s own mistake, a section 93A claim may still be available within its 4-year window.

We bought a company. Are its old tax years our problem?

The tax liability stays with the company you bought, so any year still open to IRAS remains a risk for its new owners. Ask for the target’s filed returns, notices and computations for every open YA during due diligence.

Need help with an old tax error?

If your company has found a mistake in an earlier return, contact the Raffles Corporate Services team at [email protected] or on WhatsApp at +65 8501 7133. We can review the earlier tax computations and GST returns, work out which years are still open, quantify the tax effect, and prepare the section 93A claim, voluntary disclosure or GST F7 with the supporting schedules. This article is general information, not tax advice.

Kevin Yeo, Raffles Corporate Services