Form C-S is due 30 November. What to check in the last month
30 November is the date every Singapore company files its corporate income tax return for the current Year of Assessment: Form C-S, Form C-S (Lite) or Form C. If yours isn’t filed yet, you have about four weeks. This is what has to be true before you press submit, the claims small companies most often leave on the table, and what to do if you can’t make it.
In this article
Which form you file
There are three versions. Form C-S (Lite) is for the smallest companies with simple affairs, Form C-S is for small companies that meet IRAS’s qualifying conditions, and Form C is for everyone else. Which one you qualify for depends on your revenue and on conditions IRAS sets, and those can change, so check what myTax offers you rather than going by what you filed last year.
Two things catch people out. A company that made a loss still has to file. And a dormant company doesn’t simply skip the return: it can apply to IRAS for a waiver, but until that’s granted, the filing obligation stands.
Four things that must exist before you file
- Finalised accounts for the financial year. Management accounts or a bank-statement summary aren’t enough. The figures on the return come from accounts the directors have approved.
- A tax computation. Accounting profit isn’t taxable profit. The computation adds back what isn’t deductible, takes out what isn’t taxable, and claims capital allowances. Form C-S doesn’t ask you to attach it, but IRAS can ask for it later, and you’ll need it to answer.
- Corppass access with the right role. Whoever files needs the corporate tax filing role for your company in Corppass, or your tax agent needs to be authorised. Sorting this out on 29 November is a common way to miss the date.
- Numbers that agree with ACRA. The revenue and profit you report to IRAS should match the financial statements behind your annual return. Two different sets of figures is the kind of mismatch that invites questions.
What small companies most often get wrong
From the returns we review for companies coming to us from elsewhere:
- Capital allowances not claimed. Laptops, equipment, renovation and furniture bought during the year sit in the accounts as assets, and nobody claims the allowance. That’s tax overpaid. Our capital allowances guide explains how they work.
- Private car costs claimed. Expenses on S-plated private cars are generally not deductible, even when the car is used for business. Claiming them is one of the most common things IRAS adjusts.
- Losses and allowances from earlier years forgotten. Unused losses and capital allowances can usually be carried forward, subject to conditions such as a test on whether the shareholders are substantially the same. If last year’s return showed a loss, check it’s being used this year.
- The ECI and the final return don’t talk to each other. Your Estimated Chargeable Income was an estimate. If the final figure is very different, be ready to explain why.
- Personal and company spending mixed. Owner expenses booked through the company are not deductible, and they make the whole return harder to defend.
If you’re going to be late
Don’t go quiet. If a return isn’t filed, IRAS can issue an estimated assessment, and you then owe tax on IRAS’s estimate rather than your actual profit. Penalties follow, and repeated failure to file can end with the directors summoned to court. We don’t quote penalty amounts because they change, but the pattern is consistent: the longer it’s left, the more it costs.
A late return is far better than no return. If you know you’ll miss the date, file as soon as you can, and get someone who knows the process to talk to IRAS on your behalf.
A four-week plan
Week 1: close the books for the financial year: bank reconciled, invoices and receipts in, fixed asset purchases listed.
Week 2: finalise the accounts and get the directors to approve them.
Week 3: prepare and review the tax computation. Check capital allowances, disallowed expenses and anything carried forward.
Week 4: file. Aim for a few days before 30 November, not the day itself; you don’t want a Corppass problem at 11pm.
If you’re already past week 1 with nothing closed, that’s the sign to hand it over now.
Where we come in
This is the busiest month of our year, and we still take on returns in November. We close the books, finalise the accounts, prepare the tax computation and file, and we check the claims above as a matter of routine. If you’ve already done the accounts yourself, we can review the computation before you file. See our tax services and accounting & bookkeeping.
Common questions
When is Form C-S due?
Every Singapore company files its corporate income tax return, Form C-S, Form C-S (Lite) or Form C, by 30 November for the current Year of Assessment.
Do I have to file Form C-S if my company made a loss?
Yes. A loss-making company still files. A dormant company can apply to IRAS for a waiver, but until it's granted, the obligation to file stands.
Do I need to submit my tax computation with Form C-S?
You don't attach it to Form C-S, but you need one to work out the figures, and IRAS can ask for it later.
What happens if I miss the 30 November deadline?
IRAS can issue an estimated assessment, so you owe tax on their estimate, and penalties follow. Repeated failure to file can lead to the directors being summoned to court. File as soon as you can.
Which expenses are commonly disallowed?
Expenses on S-plated private cars, the owner's personal spending booked through the company, and capital items claimed as expenses instead of through capital allowances.
Four weeks left and nothing closed?
Tell us your financial year end and where your books stand. We’ll tell you honestly whether 30 November is still realistic, and what it takes to get there.
This article is general information about corporate income tax filing in Singapore as at Nov 2026, not tax advice. Eligibility for each form, deductibility and penalties depend on IRAS’s current rules and your company’s facts. Morphrix Pte. Ltd. (formerly AG Solutions).