Every Singapore company, active or dormant, must file a Corporate Income Tax Return with the Inland Revenue Authority of Singapore (IRAS) each year. Pick the wrong form or miss 30 November, and IRAS issues penalties. Three returns exist: Form C-S, Form C-S (Lite), and Form C. Which one you file depends on your revenue and the tax claims you make, as set out in IRAS’s overview of Form C-S/ Form C-S (Lite)/ Form C-form-c-filing/overview-of-form-c-s-form-c-s-(lite)-form-c).
This guide covers all three forms for Year of Assessment (YA) 2026, the eligibility rules, the myTax Portal process, and the penalties for filing late.
What are Form C-S, Form C-S (Lite), and Form C?
They are the three variants of Singapore’s Corporate Income Tax Return, filed once a year per Year of Assessment (YA). A YA is the year in which income is taxed. It always follows the basis period, which is the financial year the income was earned. IRAS confirms the same return applies whichever form you use.
Here is a worked example. A financial year ending 31 December 2025 is the basis period for YA 2026. The return for that income is filed in 2026 and is due 30 November 2026. Companies with a non-December financial year-end map to a YA the same way: the financial year ending in 2025 falls under YA 2026.
Form C-S vs Form C: which form does your company file?
Your revenue and your tax claims decide the form. Singapore-incorporated companies with revenue of S$5 million or below and simple tax affairs file Form C-S, or Form C-S (Lite) at S$200,000 or below. Everyone else files Form C. The table below compares all three, per IRAS.
| Feature | Form C-S (Lite) | Form C-S | Form C | Source |
|---|---|---|---|---|
| Annual revenue threshold | ≤ S$200,000 | ≤ S$5 million | No limit / above S$5 million | IRAS |
| Incorporated in Singapore | Required | Required | Not restricted | IRAS |
| Income taxed only at 17% | Required | Required | Not required | IRAS |
| Special claims (group relief, foreign tax credit, etc.) | Not allowed | Not allowed | Allowed | IRAS |
| Financial statements and tax computation filed with the return | No (keep, submit on request) | No (keep, submit on request) | Yes | IRAS |
| Number of fields | About 6 | About 18 | Full return | IRAS |
Per IRAS-form-c-filing/overview-of-form-c-s-form-c-s-(lite)-form-c), Form C-S (Lite) needs only about 6 essential fields, against about 18 for the standard Form C-S.
What are the Form C-S eligibility criteria?
A company must meet all four conditions to file Form C-S, per the IRAS Form C-S FAQ. It must be incorporated in Singapore, have annual revenue of S$5 million or below, derive income taxable only at the prevailing 17% corporate tax rate, and not claim carry-back of capital allowances or losses, group relief, investment allowance, or foreign tax credit and tax deducted at source.
Being “newly incorporated” is not a condition, despite what some guides claim. Age does not matter; the four tests above do. IRAS also grants an administrative concession: a company that filed Form C-S in YA 2025 can still file Form C-S in YA 2026 even if YA 2026 revenue exceeds S$5 million, provided all other conditions hold, per the IRAS Form C-S FAQ. Non-Singapore-incorporated companies and Singapore branches of foreign companies cannot use Form C-S at all and must file Form C, per IRAS.
Who qualifies for Form C-S (Lite)?
Companies that meet every Form C-S condition and have annual revenue of S$200,000 or below qualify for Form C-S (Lite), per IRAS. It is a simplified version of Form C-S, available since YA 2020, requiring only about 6 essential fields versus about 18 for the standard form, per the IRAS overview-form-c-filing/overview-of-form-c-s-form-c-s-(lite)-form-c).
Form C-S (Lite) suits micro and small companies with straightforward tax affairs. New Singapore subsidiaries set up as cost centres with little or no first-year revenue often land here. Like Form C-S, it does not require financial statements or a tax computation to be filed with the return; you prepare and keep them for submission on IRAS request.
When must a company file Form C?
Form C is the default full return for any company that fails a Form C-S condition, per IRAS. That includes revenue above S$5 million, claims such as group relief or foreign tax credit, income taxed at concessionary rates, and foreign-incorporated companies or Singapore branches. Unlike the C-S forms, Form C requires financial statements, a tax computation, and supporting schedules to be filed with the return.
Concessionary rates are below the standard 17%. Under incentive schemes such as the Development and Expansion Incentive, qualifying income is taxed at a reduced rate. Because that income is not taxed only at 17%, the company cannot use Form C-S and must file Form C.
Do you need to file ECI before Form C-S?
Yes. Estimated Chargeable Income (ECI) is a separate, earlier filing due within 3 months of the financial year-end, per the IRAS ECI guidance-filing). ECI is an estimate of taxable income. Form C-S/C is the actual return, due 30 November. They are two filings, not one.
A company is waived from filing ECI only if annual revenue is S$5 million or below and ECI is nil for the YA, per IRAS. The trap: an ECI waiver never removes the Form C-S/C obligation. You still file the annual return. For a full walkthrough, see Commenda’s guide to Estimated Chargeable Income (ECI) filing in Singapore.
What is the corporate tax filing deadline for YA 2026?
The deadline is 30 November 2026 for YA 2026, covering any financial year ending in 2025, per IRAS’s due dates. One single e-Filing deadline applies to all three forms. Paper filing has been phased out, e-Filing is compulsory, and the old 15 December e-Filing deadline no longer exists.
| Financial year-end (FYE) | Year of Assessment | Filing deadline | Source |
|---|---|---|---|
| Any date in 2025 (e.g. 31 Dec 2025) | YA 2026 | 30 November 2026 | IRAS |
| Any date in 2026 (e.g. 30 Jun 2026) | YA 2027 | 30 November 2027 | IRAS |
Track every filing date across your entities with Commenda’s compliance calendar.
What documents do you need to file Form C?
Form C requires financial statements, a tax computation with supporting schedules, and the return’s compliance declarations, all filed with the form, per IRAS. Form C-S and Form C-S (Lite) filers prepare and keep the same documents but submit them only if IRAS asks. Companies must retain proper records for at least 5 years.
When do financial statements need to be audited?
Financial statements must be audited unless the company qualifies as a “small company” exempt from statutory audit under the Companies Act. A private company qualifies if it meets at least 2 of 3 criteria for the two immediately preceding financial years, per ACRA’s audit exemption rules.
| Small company audit-exemption criterion | Threshold | Source |
|---|---|---|
| Total annual revenue | ≤ S$10 million | ACRA |
| Total assets | ≤ S$10 million | ACRA |
| Number of employees | ≤ 50 | ACRA |
A newly incorporated company needs to meet the criteria for the current financial year only, per ACRA. These S$10 million thresholds are the audit test and are separate from the S$5 million Form C-S revenue threshold.
What declarations does the return include?
The return includes compliance declarations that confirm the company’s tax obligations, per IRAS. These cover related-party transactions, where the company declares that transactions with related parties are conducted at arm’s length. Companies above the reporting threshold must submit a Form for Reporting Related Party Transactions with the return.
For companies with cross-border related-party dealings, Commenda’s transfer pricing service prepares the documentation that supports these declarations.
What are tax adjustments in the tax computation?
Tax adjustments reconcile the accounting profit in your financial statements to chargeable income under Singapore tax law, because accounting and tax treatments differ. The tax computation applies these adjustments to arrive at the income IRAS actually taxes.
Three common adjustments show how it works. You add back non-deductible expenses, such as fines and private car expenses. You replace accounting depreciation with capital allowances. You remove non-taxable income, such as qualifying foreign-sourced dividends that are exempt when conditions are met. Each adjustment moves the accounting figure closer to chargeable income.
How do you file Form C-S on myTax Portal step by step?
File at mytax.iras.gov.sg after Corppass authorisation, following the numbered steps below. Corppass is Singapore’s corporate digital identity for government transactions. The filer must be authorised for “Corporate Tax (Filing and Applications)” as a Preparer or Approver before login, per the IRAS Form C-S FAQ. Without it, you cannot access the return.
- Determine the correct form (Form C-S, Form C-S (Lite), or Form C) using the eligibility conditions above.
- Prepare financial statements, audited unless the company is exempt as a small company.
- Prepare the tax computation and supporting schedules.
- Log in to myTax Portal with Corppass and the company’s tax reference number.
- Complete the on-screen form and submit it. For Form C, attach the financial statements, tax computation, and schedules.
- Retain the documents for IRAS request (Form C-S / Form C-S (Lite)) or attach them (Form C), and save the acknowledgement.
Qualifying small companies can also file Form C-S directly from accounting software integrated with IRAS through Seamless Filing from Software, which pulls figures straight from the books.
Do dormant companies need to file a Singapore tax return?
Yes. Dormant companies must still file, using IRAS’s simplified “File Form C-S/ C for Dormant Company” service, unless IRAS grants a waiver of the return. A dormant company had no business activity and no income during the basis period. Until a waiver is approved, it files a nil return declaring no income.
A company can apply to IRAS for a waiver if it has ceased trading, has no intention to recommence business, and has met its prior filing obligations. Note that “dormant for tax purposes” under IRAS differs from dormancy under ACRA; see Commenda’s guide to ACRA and BizFile in Singapore.
What are the penalties for late corporate tax filing in Singapore?
IRAS enforces late or non-filing with estimated assessments, composition offers, and prosecution, per its late filing guidance-form-c-filing/late-filing-or-non-filing-of-Corporate-Income-Tax-Returns-form-c-s-form-c-s-(Lite)-form-c). An estimated Notice of Assessment (NOA) is issued on IRAS’s estimate of income, and the tax must be paid even while you object. The table sets out the specific consequences.
| Enforcement action | Amount or consequence | Source |
|---|---|---|
| Composition offer in lieu of prosecution | Up to S$5,000 per offence | IRAS |
| Estimated Notice of Assessment (NOA) | Tax on estimated income, payable within 1 month even if objecting | IRAS |
| Conviction after court summons (2+ years non-filing) | Fine up to S$5,000 per offence plus twice the tax assessed | IRAS |
| Director failing a Section 65B(3) notice | Fine up to S$10,000 or up to 12 months jail, or both | IRAS |
An estimated assessment does not remove the obligation to file, and the estimate is often higher than the actual tax.
How Commenda helps with Singapore corporate tax filing
Commenda’s corporate tax and bookkeeping service prepares your financial statements and tax computation and files Form C-S, Form C-S (Lite), or Form C on time, so controllers know their Singapore annual filing is handled. Where the return’s related-party declarations apply, Commenda’s transfer pricing service prepares the documentation that supports them. For the earlier estimate, start with Commenda’s guide to Estimated Chargeable Income (ECI) filing.
Book a demo to get your Singapore YA 2026 filing calendar mapped before the 30 November deadline.
