Every Singapore company that derives income from any source must file a corporate income tax return with IRAS every year. The form you file, however, depends on the size and complexity of your business — and choosing the wrong one wastes hours of preparation time or, worse, attracts an IRAS review.
For Year of Assessment (YA) 2026, IRAS continues to offer three corporate tax return forms: Form C-S, Form C-S (Lite), and Form C. This guide explains which one applies to your company, the documents each requires, the filing deadlines, and the practical pitfalls our team sees most often.
Why IRAS Has Three Forms
The three forms exist to scale compliance effort to business complexity. The smallest, simplest companies fill in the simplest form. Large or complex companies file the full Form C with detailed schedules and supporting documents. The intermediate Form C-S sits in between — short enough to be friendly, but with enough detail for IRAS to triangulate.
At the heart of the system are two qualifying tests: annual revenue and business profile. A company that meets both qualifying tests for Form C-S (Lite) may elect to file the lightest return; a company that fails either drops to Form C-S or Form C as the case may be.
Form C-S (Lite) — The 6-Field Simplified Return
Form C-S (Lite) is the shortest of the three, requiring only 6 essential fields to be completed. It was introduced to streamline filings for very small companies and remains a strong fit for owner-managed SMEs.
To qualify, the company must satisfy ALL of the following:
- Be incorporated in Singapore;
- Have an annual revenue of S$200,000 or less for the relevant YA;
- Derive only income taxable at the prevailing corporate tax rate (currently 17 percent);
- Not be claiming any of the following in the YA: carry-back of capital allowances or losses, group relief, investment allowance, Section 13(1) tax exemption, foreign tax credit or tax deducted at source.
The 6 fields cover revenue, adjusted profit/loss before exempt amount, exempt income, chargeable income before exempt amount, partial tax exemption, and tax payable. No financial statements or tax computation needs to be filed — but they must still be prepared and retained for the IRAS retention period of 5 years.
Form C-S — For Most Small Singapore Companies
Form C-S is the workhorse return used by the vast majority of small Singapore SMEs that exceed the S$200,000 revenue ceiling. It is shorter than the full Form C and does not require submission of financial statements, tax computation or detailed schedules at the point of filing.
Qualifying conditions for Form C-S:
- Incorporated in Singapore;
- Annual revenue of S$5 million or less for the YA;
- Derives only income taxable at the prevailing corporate tax rate;
- Not claiming any of the items listed under the Form C-S (Lite) restrictions above (group relief, investment allowance, FTC, etc.).
Although the return itself is short, the company must still prepare full tax-adjusted accounts, a tax computation and supporting schedules, and produce them within 30 days if IRAS calls for them.
Form C — The Full Return
Form C is the default return required of any company that does not qualify for Form C-S or Form C-S (Lite). It requires submission, at the point of filing, of:
- Financial statements (audited or unaudited, depending on the company’s audit-exemption status);
- Detailed tax computation;
- Supporting schedules for capital allowances, deductions, losses carried forward, group relief etc.;
- Form for Reporting Related Party Transactions (RPT Form) where applicable.
Companies that must file Form C include those:
- With annual revenue above S$5 million;
- Claiming foreign tax credit, group relief, investment allowance, carry-back relief or any incentive other than partial tax exemption;
- With income taxed at concessionary rates (e.g. companies under Pioneer, Development & Expansion Incentive, Section 13O/13U for family offices);
- Operating regulated financial sector activities;
- Holding tax-incentive certificates from EDB or MAS.
Side-by-Side Comparison
| Criterion | Form C-S (Lite) | Form C-S | Form C |
|---|---|---|---|
| Revenue ceiling | ≤ S$200,000 | ≤ S$5 million | No ceiling |
| Number of fields | ~6 essential fields | Reduced (no schedules at filing) | Full return + schedules |
| Financial statements at filing | Not required | Not required | Required |
| Tax computation at filing | Not required | Not required | Required |
| Group relief / FTC / investment allowance | Not allowed | Not allowed | Allowed |
| Concessionary tax rate income | Not allowed | Not allowed | Allowed |
| Filing deadline | 30 Nov (e-filing) | 30 Nov (e-filing) | 30 Nov (e-filing) |
Filing Deadlines and ECI
Whichever form your company files, the YA filing flow is the same:
- ECI: File the Estimated Chargeable Income (ECI) within 3 months after FYE. Companies with revenue ≤ S$5m and ECI of nil are exempt from ECI filing.
- Tax Form: File Form C-S (Lite), Form C-S or Form C by 30 November of the YA.
- Tax Payment: Pay the tax assessed (NOA) within 1 month from the date of NOA, or via GIRO over up to 12 months.
Need a fuller picture of corporate tax rates and the partial exemption rules? Read our Singapore Corporate Tax 2026 guide.
Common Mistakes We See
- Filing Form C-S despite claiming group relief. If your company is claiming group relief from a related Singapore company, you must file Form C — even if revenue is below S$5m.
- Missing the related-party threshold. Companies with related-party transactions exceeding S$15m in aggregate must complete the RPT Form. This sometimes pushes a company from Form C-S to Form C in practice.
- Over-stating revenue. Revenue means the company’s principal income, not the gross top-line including disposal gains and reversals. Misclassifying capital receipts as revenue can inflate the figure past the C-S threshold.
- Filing on paper. Paper filing has been discontinued — all returns must be e-filed via myTax Portal.
- Forgetting the 5-year retention rule. Even Form C-S (Lite) filers must retain the underlying records for at least 5 years. Section 199 of the Companies Act imposes a parallel record-keeping requirement.
What Happens If You File the Wrong Form?
IRAS will typically reject the return and ask the company to refile using the correct form. There is no fine for filing the wrong form, but the refile delays issuance of the Notice of Assessment and increases the risk of late filing if the 30 November deadline is missed in the process. Worse, repeated incorrect filings flag the company for review.
If you only realise mid-prep that your company should be filing Form C, do not file Form C-S and “fix it later”. File Form C from the outset — and budget for the additional accounting work to produce financial statements and a tax computation.
How Raffles Corporate Services Handles This
For SME clients, our team computes the qualifying tests early in the year — usually as part of the ECI filing — and locks in the right form before the November deadline. We prepare the tax-adjusted accounts and computation regardless of which form is filed, so the underlying records are audit-ready. For groups with intercompany lending, FTC claims or transfer-pricing requirements, we walk clients through the additional Form C schedules and the Transfer Pricing Documentation rules.
FAQ
Can a dormant Singapore company use Form C-S (Lite)?
Yes — provided revenue is zero and the company has no other disqualifying claim. Many dormant companies use Form C-S (Lite) or the dormant simplified e-Service to file a nil return.
Does Form C-S apply if my company has only Singapore-sourced rental income?
Yes, if the rental income is taxable at the prevailing corporate tax rate and the company does not claim any disqualifying item. Most small property-holding companies use Form C-S.
Can I switch from Form C to Form C-S in the following year?
Yes — eligibility is tested annually. If revenue drops below S$5m and no disqualifying items apply, the company can elect Form C-S for the new YA.
Are the deadlines the same for all three forms?
Yes. All three forms must be e-filed by 30 November of the YA.
— The Editorial Team, Raffles Corporate Services