Singapore tax filing deadlines: GST, corporate, and personal dates

Singapore’s tax calendar is compact compared with its peers: one GST date that repeats, two corporate milestones, and a single personal filing window. The catch is the Year of Assessment system, which offsets corporate deadlines a year from the activity they describe and regularly confuses founders new to the jurisdiction. The dates below are verified against IRAS sources in the Sources section.

GST: one month, every period

For GST-registered businesses, the F5 return and the payment are both due one month after the end of the accounting period ^[1] . On the standard quarterly cycle:

GIRO payers get their deduction taken shortly after the due date automatically, which in practice makes GIRO the default risk-management move for small businesses. Note that as the GST InvoiceNow requirement phases in through 2031, the invoice data behind these returns will flow to IRAS continuously; the F5 dates themselves are unchanged.

Corporate income tax: ECI, then Form C-S

Singapore taxes companies on a Year of Assessment (YA) basis: YA 2026 covers the financial year that ended during calendar 2025. Two filings result ^{[2] [3]} :

Three practical notes:

1. The ECI waiver: companies that meet IRAS’s waiver conditions (centred on revenue within the threshold and a nil ECI) do not need to file ECI; check the current conditions on the IRAS ECI page rather than assuming ^[2] .
2. Early ECI buys instalments. Filing ECI promptly, with GIRO, spreads the tax over more monthly instalments; filing at the deadline compresses the payment schedule.
3. The November return is about last year. A company with a 31 December 2025 year end files ECI by 31 March 2026 and Form C-S by 30 November 2026, both for YA 2026.

Personal income tax (including sole proprietors)

Individuals, including sole proprietors reporting business income, file for the preceding calendar year by 18 April (e-filing) or 15 April on paper. The assessment then arrives as a Notice of Assessment, with payment due within 1 month of its date unless GIRO instalments are in place. Most taxpayers in Singapore are on GIRO, which converts the bill into interest-free monthly deductions.

If a deadline is missed

IRAS enforcement is brisk by international standards. Late or missing corporate returns draw composition amounts and, if ignored, estimated assessments based on IRAS’s own view of the company’s income, which are rarely flattering and must be paid even while you object. Late GST filing attracts penalties that grow the longer the return stays outstanding, and late payment adds a percentage penalty on the unpaid tax. The working rule for bookkeepers: never let IRAS estimate. Filing something accurate on time, then amending if needed, is always cheaper than the estimated-assessment path, and GIRO instalment plans neutralise most payment-timing risk for both corporate and personal tax.

The annual rhythm for a typical SMB

Take a GST-registered private limited company with a December year end:

• 31 January, 30 April, 31 July, 31 October: quarterly F5 and GST payment.
• 31 March: ECI for the year just ended (unless waived).
• 18 April: directors’ and any sole-proprietor personal filings.
• 30 November: Form C-S for the YA.
• Rolling: corporate and personal tax payments, one month after each NOA or via GIRO.

Every one of those filings is assembled from the same expense and revenue records, and IRAS expects the documents behind them to be producible on request. ExpenseFlow keeps that base layer current: receipts and supplier invoices are captured as they arrive, extracted and coded with the right GST treatment (including blocked input tax categories), and synced into Xero with the source document attached. The F5 gets prepared and filed from the accounting platform as usual; the difference is that the data underneath it is already reconciled when the month-end arrives.