By KYN AI Advisory Team — AI implementation specialists, Singapore
A Singapore company files Form C-S if its annual revenue is $5 million or below and it meets IRAS's income and claim conditions. It may file the shorter Form C-S (Lite) if revenue is $200,000 or below. If you do not qualify for either, you file the full Form C. All three are due by 30 November each year. The choice depends on three tests: where the company is incorporated, how much it earns, and what kind of income and claims it has.
What is the difference at a glance?
| | Form C-S (Lite) | Form C-S | Form C | |---|---|---|---| | Annual revenue | $200,000 or below | $5 million or below | Any | | Incorporated in Singapore | Required | Required | Not required | | Income taxed at 17% only | Required | Required | Not required | | Claims limited (see below) | Required | Required | Not required | | Level of detail | Fewest fields | Moderate | Fullest | | Due date | 30 November | 30 November | 30 November |
Sources: IRAS overview of Form C-S, C-S (Lite) and C-form-c-filing/overview-of-form-c-s-form-c-s-(lite)-form-c) and IRAS filing guidance-form-c-filing/guidance-on-filing-form-c-s-form-c-s-(lite)-form-c).
What are the exact conditions for Form C-S?
IRAS lists these conditions, which also apply to C-S (Lite):
- The company is incorporated in Singapore.
- It derives only income taxable at the prevailing 17% corporate income tax rate. Income that is tax exempt or taxed at concessionary rates, such as under tax incentives, generally disqualifies it, with some exceptions.
- It does not claim carry-back of current year capital allowances or losses, group relief, investment allowance, or foreign tax credit and tax deducted at source in the Year of Assessment.
- Annual revenue is $5 million or below (for C-S), or $200,000 or below (for C-S Lite).
IRAS notes that revenue refers to the company's main income source, excluding separate source income such as interest.
Do you have to use C-S (Lite) if you qualify?
No. If you qualify for the Lite form, you can still file Form C-S or Form C. Lite is an option for companies with simple affairs. A company that chooses the longer form loses nothing except time.
Which form suits which company?
| Company | Likely form | Why | |---|---|---| | New consultancy, S$120,000 revenue, no claims | C-S (Lite) | Under $200,000, simple income | | Design studio, S$1.8 million revenue, Singapore customers | C-S | Between thresholds, 17% income | | Trading firm, S$4 million revenue, group relief claimed | C | Group relief rules out C-S | | Software firm, S$900,000 revenue, tax incentive on part of income | C | Concessionary income rules out C-S | | Holding company, S$6 million revenue | C | Over $5 million | | Foreign-incorporated branch | C | Not incorporated in Singapore |
The examples are illustrative. Check the conditions against your own facts.
What do you need to prepare?
The forms differ in fields, not in the evidence behind them. Prepare:
- financial statements for the year, or the figures if unaudited;
- a reconciliation from accounting profit to taxable profit: add back non-deductible items, deduct non-taxable income;
- capital allowance schedule for fixed assets;
- the ECI you filed, or the reason you did not;
- the GST figures, if registered, for reference;
- the company's tax reference, and a login with authority to file.
For Lite, the form asks for a small set of figures, such as revenue, total expenses, and chargeable income. For C-S, you add more detail, such as the breakdown of items in the tax computation.
Keep the working papers with the records. IRAS requires companies to keep records for at least five years from the relevant Year of Assessment. See what to keep and for how long.
What is the timeline?
For a December year end:
| Step | When | |---|---| | Financial year ends | 31 December | | ECI due, unless waived | Within 3 months of year end (IRAS-filing)) | | Accounts finalised | Usually within 3 to 5 months | | Form C-S, C-S (Lite) or C due | 30 November of the following year |
The 30 November date applies to every year end. A company with a June year end has about 17 months from year end to filing, and a company with a December year end about 11. See the full 2027 deadline calendar.
What mistakes do companies make?
- Using Lite when a condition fails. Concessionary-rate income, or a claim such as group relief, takes you out of both C-S forms.
- Reading revenue wrongly. Revenue is the main income source. Do not add interest or other separate-source items when testing the threshold.
- Skipping ECI when revenue exceeds $5 million with nil ECI. The waiver needs both revenue at or below $5 million and nil ECI.
- Filing before the accounts are final. An amended return costs more time than waiting a week.
- Not saving the acknowledgement. Save the filing confirmation with the working papers.
How does the revenue test work in practice?
Take a company that bills S$3.2 million in services and earns S$18,000 in bank interest. IRAS treats revenue as the main income source and excludes separate source income such as interest, so the test uses S$3.2 million. The company is under the $5 million line, and the interest does not push it over.
Now take a company with S$4.9 million of sales that signs a large contract mid-year and ends the year at S$5.3 million. It moves from Form C-S to Form C for that Year of Assessment. Watch revenue through the year, not only at close, so the move to the fuller form does not surprise your accountant in October.
Revenue is also the test for the ECI waiver, which uses the same $5 million figure together with a nil ECI. Both thresholds are in the IRAS pages linked above.
What should you check each year?
- Revenue against both thresholds, using the main income source.
- Whether any income is exempt or taxed at a concessionary rate.
- Whether you plan to claim group relief, carry-back of current-year losses or capital allowances, investment allowance, or foreign tax credit.
- Whether the company is still incorporated in Singapore.
- Whether the ECI was filed or the waiver applied.
Write the answers in a one-page checklist and keep it with the working papers. The checklist also shows next year's accountant why you chose a form.
Can a system help?
It can do the repeatable parts: pull revenue and expense totals from the ledger, list add-backs flagged during the year, compute capital allowances from the asset register and pre-fill the working paper. A person reviews the computation and approves the submission, because a filing is a statement to a tax authority.
If your ledger is clean, the form takes minutes. If it is not, no form fixes that. A reconciled ledger and an audit trail come first; read what an audit trail is.
Where KYN fits
KYN builds finance systems in a cloud account in your name. In our own books, bills are read from Gmail into the ledger and GST is tracked by quarter. A system can prepare the revenue and expense totals and the working paper for your accountant. Filings wait for a named person, and every action is logged with the actor.
The 14-day review checks your revenue profile and what your accountant already receives from you. A full build ships in under 90 days. See finance systems.
Frequently asked questions
Can I switch from C-S (Lite) to C-S in a later year?
Yes. The form is chosen each year by the conditions in that year. If revenue grows above $200,000, you move to C-S, as long as you still meet the C-S conditions.
Does a loss-making company still file?
Yes. A company files each year, including when it has a loss or no activity. Check with your accountant on how a dormant company reports.
Who can file the return?
An authorised officer of the company, or a tax agent appointed by the company, through IRAS's online service. The company remains responsible for the content.
Checked 30 October 2026.
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