Tax season can be confusing for a lot of small business owners in Singapore [1]. There are a lot of terms out there, like “ECI,” “Form C-S,” “YA,” and “NoA.” But what do they really mean for your daily work?
The good news is that Singapore’s territorial tax system is one of the best for businesses in the world [2]. The bad news is that mistakes in filing automatically lead to penalties, notices of assessment, and IRAS questions that you don’t want [3].
This guide cuts through the jargon. This is how corporate tax works in Singapore for the Year of Assessment (YA) 2026, whether you are filing for the first time or have been doing it for a long time.
Part A: What is the Year of Assessment (YA)?
You don’t have to pay taxes on the money you make this year in Singapore. You pay taxes the year after [2].
- Fiscal Year (FY): The time frame in which your business files its taxes (for example, from January 1, 2025, to December 31, 2025).
- Year of Assessment (YA): The year when income earned in the previous fiscal year is taxed.
Example: Income earned in FY2025 is taxed in YA2026.
☐ Make sure you know when your company’s financial year ends (FYE).
☐ Find your YA that goes with it.
Part B: ECI, or the Estimated Chargeable Income
What is it?
ECI is an estimate of how much money your business will make in taxes for a year. It is not the last tax return [1].
Who files?
- All businesses must file ECI, unless they meet the requirements for the ECI Waiver.
- ECI Waiver Requirements: ECI is nil and annual revenue is less than S$5 million [4].
Due Date:
- Within three months of the company’s FYE.
Example: FYE 31 Dec 2025 → ECI due 31 Mar 2026.
☐ Figure out how much money you think you’ll make after taxes, expenses that are allowed, and capital allowances.
☐ Use the IRAS myTax Portal to file [5].
☐ Pay the estimated tax within 30 days of getting the Notice of Assessment (NoA) from IRAS [3].
⚠️ Common Trap: “Not paying taxes” means “not having to file.” You still have to file a NIL ECI even if your ECI is zero, unless you qualify for the full waiver [4].
Part C: Form C, Form C-S, and Form C-S (Lite)
This is the last tax return. It tells the YA how much money your business really made [2].
| Form Type | Who Can Use? | Key Requirements |
| Form C-S (Lite) | Annual revenue ≤ S$200,000 | 4-box declaration; no financial statements attached |
| Form C-S | Annual revenue ≤ S$5 million | Must meet audit exemption criteria; no tax adjustments required |
| Form C | All other businesses | Full financial statements and detailed tax calculations |
Due Date:
- The YA’s 30th of November.
- No extensions allowed. You must file electronically [5].
☐ Get ready to make full financial statements, both audited and not.
☐ Make a tax computation by comparing accounting profit to tax profit.
☐ File through the myTax Portal.
☐ Pay any taxes you owe within 30 days of receiving your NoA [3].
Part D: Common Mistakes People Make When Filing IRAS (And How to Avoid Them)
Mistake #1: Filling out the wrong form
When revenue is more than S$5 million, use Form C-S. The IRAS will turn down the filing and charge late fees [6].
Mistake #2: Wrong revenue declaration
The revenue you report on Form C-S must match what your financial statements say. IRAS checks ACRA data against its own [7].
Error #3: Not making tax changes
Profit for accounting purposes is not the same as profit for tax purposes [1]. Some common changes are:
- Expenses that are not allowed: personal cars, capital expenses, and donations (unless they are made through approved IPCs) [2].
- Capital allowances can be claimed for plant, machinery, and some renovation or refurbishment work [8].
Mistake #4: Late ECI = Late Payment Fees
If you file ECI on time but don’t pay the estimated tax on time, you’ll have to pay a 5% penalty plus 1% interest every month [3].
Part E: myTax Portal for IRAS Digital Services
All corporate tax returns in Singapore are filed online [5].
Important Features for Businesses That File:
- Information that is automatically filled in: The names of directors and shareholders are already filled in.
- View Notices of Assessment (NoA): Get them right away after the assessment.
- Ways to Pay: GIRO (highly recommended), PayNow Corporate, or AXS.
- Appeal/Objection: You have 30 days from the date of NoA to file an objection [3].
☐ Make sure your Corppass administrator gives you “Tax Agent” or “Finance” access [5].
☐ Set up GIRO so that your taxes are paid automatically (to avoid late fees).
Part F: Simple Tax Planning Tips for Small Businesses (2026)
1. Plan Your Capital Spending
You can claim capital allowances on assets you buy and use during the financial year. If you want to buy equipment, do it before your FYE so you can claim it in the current YA [8].
2. Deduction for Renovation and Repair
You can claim up to S$300,000 for qualifying renovation work over three consecutive YAs [8].
3. Get the most out of the Corporate Income Tax Rebate
The corporate tax rebate, which is usually 20–50% of the tax owed, is expected to last until 2026. Keep an eye on IRAS announcements [9].
4. The Loss Carry-Back Plan
If your business loses money in YA2026, you can carry it back up to 1 YA to lower the taxable income from the previous year, but only if certain conditions are met [2].
5. Transactions with Related Parties
Make sure that all transactions with directors and shareholders are properly recorded and done at arm’s length. Loans that aren’t backed up may be treated as dividends [7].
Part G: How PC Lee Helps You File Your Business Taxes
We don’t just fill in boxes at PC Lee & Co. Our corporate tax services Singapore team, who are all Certified Public Accountants, takes a “holistic” approach [10]:
1. Early ECI Filing
As soon as we finish your management accounts, we file your ECI. No waiting until the three-month deadline.
2. Calculating and Changing Taxes
We find every deduction and capital allowance that is allowed. What we want to do: Pay as little tax as possible and follow the rules as much as possible.
3. Getting Ready for Form C / C-S
We make sure that your financial statements meet IRAS standards. We do full tax calculations and make supporting schedules for people who file Form C.
4. Letters from IRAS
If IRAS has questions, we answer them in a professional way, so you won’t have to deal with any “letter from IRAS” stress.
5. Review of Tax Planning
After you file, we look over your business structure and transactions to find ways to save money on taxes in the future.
How Much We Charge:
- Form C-S (Lite): A set fee of S$400
- Form C-S: A set fee of S$600
- Form C (Full): The price is based on how complicated the transaction is [10]
Corporate Tax Filing Deadlines at a Glance (YA 2026)
| Task | Deadline | Form |
| File ECI | Within 3 months of FYE | myTax Portal |
| Pay ECI Tax | Within 30 days of NoA | GIRO / PayNow |
| File Form C / C-S | 30 Nov 2026 | myTax Portal |
| Pay Final Tax | Within 30 days of NoA | GIRO / PayNow |
⚠️ Reminder: Your ECI is due on March 31, 2026, and your Form C is due on November 30, 2026, if your FYE is December 31, 2025.
Don’t File Alone—Get Help from Professionals
Filing corporate taxes is not just a duty; it’s a strategic exercise [1]. You lose money when you miss deductions. You will have to pay fines if you file late. Mistakes cause IRAS audits [6].
PC Lee & Co offers complete IRAS tax filing services Singapore small and medium-sized businesses and foreign subsidiaries can rely on [10]. We offer accurate, timely, and stress-free help with filing taxes once or all year long.
[Get in touch with our tax team today] to get a quote with a set fee. We can take care of the numbers while you grow your business.
This guide is based on the rules for Singapore corporate taxes for the Year of Assessment 2026. We keep an eye on budget announcements and changes to the law all the time, and we send proactive updates to PC Lee clients.
References[1] Inland Revenue Authority of Singapore (IRAS). (2025). Corporate Income Tax Guide for New Companies.
[2] IRAS. (2025). Singapore’s Territorial Tax System and Basis of Taxation.
[3] IRAS. (2025). Late Filing and Late Payment Penalties for Corporate Tax.
[4] IRAS. (2024). Estimated Chargeable Income (ECI) Filing and Waiver Criteria.
[5] IRAS. (2025). myTax Portal – Corporate Tax Filing User Guide.
[6] IRAS. (2024). Common Errors in Form C-S Filing and How to Avoid Them.
[7] Accounting and Corporate Regulatory Authority (ACRA), Singapore. (2025). Financial Reporting and Tax Alignment.
[8] IRAS. (2025). Capital Allowances and Renovation & Refurbishment Deduction Schemes.
[9] Ministry of Finance, Singapore. (2025). Singapore Budget 2025 – Tax Measures and Corporate Rebates.
[10] PC Lee & Co. (2025). Corporate Tax Compliance and Advisory Services.