Corporation Tax Refund: How to Get Money Back If You Overpaid HMRC
If your company has overpaid corporation tax, you're entitled to a refund from HMRC. Whether the overpayment happened because of an accounting error, a change in your tax calculation, or because you paid too much on account, getting that money back is straightforward — once you know the process.
This guide explains when corporation tax refunds arise, how to claim them, and how long you should expect to wait.
When Do Corporation Tax Overpayments Happen?
There are several common scenarios where a company ends up paying more corporation tax than it owes:
- Estimated payments were too high — You made a payment on account based on estimated profits, but your actual profits were lower.
- Expenses or reliefs were missed — Your original CT600 didn't include all allowable deductions (e.g. capital allowances, R&D tax relief, or losses brought forward).
- Accounting errors — A mistake in your accounts overstated profits.
- Loss carry-back — Your company made a loss in a later period and you're carrying it back to an earlier profitable year under the loss relief rules.
- Marginal relief miscalculation — If your profits fall between £50,000 and £250,000, marginal relief reduces your effective tax rate. Getting this wrong can mean overpaying.
How to Claim a Corporation Tax Refund
Option 1: HMRC Processes It Automatically
When you file your CT600 and the tax calculated is less than what you've already paid, HMRC will usually issue a refund automatically. This typically happens within a few weeks of your return being processed.
The refund is sent to the bank account HMRC has on file for your company, or by payable order (cheque) if no bank details are registered.
Option 2: Amend Your CT600
If you've already filed your CT600 and later realise you overpaid — perhaps because you missed an expense or relief — you'll need to amend your return.
You can amend a CT600 within 12 months of the original filing deadline. For most companies, the filing deadline is 12 months after the end of the accounting period, giving you up to 24 months from the end of the accounting period to submit an amendment.
To amend:
- Log in to HMRC's online services or your filing software.
- Submit a revised CT600 with the corrected figures.
- Include updated computations and iXBRL accounts if the underlying figures have changed.
HMRC will process the amendment and issue a refund for the difference.
Option 3: Write to HMRC
If the amendment window has closed (more than 12 months after the filing deadline), you can still make a claim for overpayment relief. This must be made in writing within 4 years of the end of the relevant accounting period.
You'll need to explain why the original return was incorrect and provide supporting evidence.
How Long Does a Corporation Tax Refund Take?
Typical timelines:
| Scenario | Expected Wait |
|---|---|
| Automatic refund after filing | 2–4 weeks |
| After CT600 amendment | 4–6 weeks |
| Overpayment relief claim (written) | 8–12 weeks |
| Complex cases or HMRC enquiry | 3–6 months+ |
If your refund is delayed beyond the normal processing time, you can contact HMRC's Corporation Tax helpline on 0300 200 3410.
Interest on Corporation Tax Refunds
HMRC pays interest on overpaid corporation tax from the date the tax was paid (or the normal due date, whichever is later) to the date the refund is issued.
The repayment interest rate is set by HMRC and tracks the Bank of England base rate. From 9 January 2026, the repayment interest rate is 2.75% (though this changes — always check the HMRC interest rates page).
Note that repayment interest is taxable — it counts as income for your company in the period it's received.
Corporation Tax Refund and Your CT600
When you submit or amend your CT600, the key boxes to check are:
- Box 525/528 — Self-assessment of tax payable (this should reflect the correct, lower amount after amendment)
- Box 605 — Tax overpaid (the amount HMRC will repay if your credits and prior payments exceed your liability)
If you're carrying back a trading loss from a later period to reclaim tax paid in an earlier year, the claim is made on the main CT600 form — there are no supplementary pages for a standard loss carry-back. On the amended earlier-period return, enter the loss being carried back in box 275 and tick box 280 to confirm the figure includes an amount carried back from a later period. You should also tick box 45 ("Claim or relief affecting an earlier period") to flag the amendment to HMRC. Note that you cannot make a carry-back claim until the return for the loss period has been delivered.
Common Mistakes When Claiming Refunds
- Not updating iXBRL accounts — If your amendment changes the underlying accounts, you must submit updated iXBRL-tagged accounts alongside the revised CT600.
- Missing the amendment deadline — You only have 12 months from the filing deadline. After that, the process becomes more complex.
- Forgetting about associated companies — If you have associated companies, the £50,000 and £250,000 thresholds for marginal relief are divided. Getting this wrong affects your tax rate.
- Not checking bank details with HMRC — Refunds go to the bank account on file. If those details are outdated, your refund could be delayed.
File Your CT600 Accurately with Taxpipe
The best way to avoid overpayments is to get your CT600 right first time. Taxpipe helps UK limited companies file their CT600 directly to HMRC for just £59 — with built-in checks for marginal relief, capital allowances, and common errors. No accountant needed.