If your company has paid too much corporation tax in the UK, you can reclaim it directly from HMRC. Yes, by filing or amending your Company Tax Return (CT600).
For 2026/27, the key thing to know is that HMRC’s current repayment interest rate is 2.75% from 9 January 2026. And it’s 3.50% for Company Tax quarterly instalment payments. So remember that there can be a small amount of interest on a valid corporation tax refund HMRC processes.
If you think your company may have paid too much, this guide walks you through exactly how to reclaim overpaid corporation tax UK, including:
- How do I amend a CT600?
- 3 ways to reclaim overpaid corporation tax UK
- How long does HMRC take to repay corporation tax?
- And much more…
Let’s get into it!
Why Do Companies Overpay Corporation Tax in the First Place?
Honestly, it happens more than you’d think. You might have missed a valid expense. Or perhaps your profits weren’t as high as you initially projected. In the 2026/27 tax year, the rules around things like R&D credits and full expensing for capital equipment have become even more detailed. It is very easy to overlook a relief that could have shaved thousands off your bill.
Another big reason Companies Overpay Corporation Tax is “loss carry-back.” If your business had a bit of a rough year and made a loss, you might be able to use that loss. This way you can offset profits from the previous year. This often results in a nice refund from tax you’ve already paid. It’s essentially a bit of a safety net which is provided by the tax system. But remember that you have to actively ask for it.
Sometimes, the overpayment happens because of how you pay. If your company is large enough to pay in quarterly instalments, you are essentially guessing your profit in advance. If the economy takes a dip or a big contract falls through, those early payments might end up being way too high. In these cases, you definitely need to reclaim overpaid corporation tax UK. This way, you can keep your cash flow healthy.
How Do I Claim Back Overpaid Corporation Tax?
To reclaim overpaid corporation tax in the UK, a few different routes are depending on your situation. The process to claim back overpaid corporation tax depends entirely on whether you’re still within the amendment window or not.
Option 1: Include It on Your Company Tax Return (CT600)
This is the easiest way to claim back overpaid corporation tax. If you are currently sitting down to do your taxes or you are just about to hit send, this is the time to act. On your Company Tax Return (CT600), you simply tell HMRC that a repayment is due. You need to tell them exactly how you want that money paid.
Make sure you put your company bank account details (sort code and account number) right there on the form. If you leave those boxes blank, HMRC won’t just guess where to send it. They usually just hold onto the money. They might offset it against your next bill instead of sending it to you. If you want the cash in your pocket to pay staff or buy stock, fill in those bank details. This way, you can reclaim overpaid corporation tax UK efficiently.
At Accotax, our limited company accountants always double-check this for our clients because nobody wants their money stuck in an HMRC holding account.
Option 2: Amend Your CT600
So you have already filed, and then you realise you missed a massive invoice or a tax relief. Don’t worry, you can still reclaim overpaid corporation tax UK by amending your return. HMRC allows amendments. But only within 12 months of the filing deadline. And not 12 months from when you filed, but from the deadline itself.
For example, if your accounting period ended on 31 March 2026, your filing deadline is 31 March 2027. That means you have until 31 March 2028. This is to fix any blunders and reclaim overpaid corporation tax UK.
How Do I Amend a CT600?
Here’s how you can amend a CT600 for 2026/27:
- Check the deadline: You have 12 months from the original filing deadline. If that has passed, you’ll need overpayment relief instead.
- Prepare your corrected figures: Update tax computation, revised accounts if needed.
- Open your CT600 in your commercial software: Locate the accounting period you want to correct and mark it as “amended”. Remember, HMRC’s free service closed in March 2026. That is why all CT600 filings and amendments now have to go through commercial filing software.
- Submit the full return: Not just the changed boxes. The whole thing, including iXBRL-tagged accounts.
- Include bank details: This is to make sure any repayment goes directly to your account when you reclaim overpaid corporation tax UK.
- Keep a copy: Record the submission receipt. And also any HMRC correspondence.
If the error involves accounting period dates, you’ll need to contact HMRC directly. Do not amend through software, as those can’t simply be resubmitted.
Option 3: Overpayment Relief Claim
What if you are looking at a mistake from three years ago? Now you have missed the 12-month amendment window. nd this is where people usually give up. But you shouldn’t. You can still reclaim overpaid corporation tax UK using something called “Overpayment Relief.” It’s governed by Schedule 1AB of the Taxes Management Act 1970.
The deadline here is four years from the end of the accounting period. So if the overpayment relates to an accounting period ending 31 March 2023, you would have until 31 March 2027 to submit your claim. After that, the window closes permanently. Yes, and you lose the chance to reclaim overpaid corporation tax UK.
For an overpayment relief claim, you have to write an actual letter to HMRC. You need to include your company name and your UTR (Unique Taxpayer Reference). You must include the specific dates, the amount you overpaid, and a very good reason why it happened. You also need to provide evidence to successfully reclaim overpaid corporation tax UK.
How Long Does HMRC Take to Repay Corporation Tax?
If you go the digital route, you’re usually looking at about 4 to 8 weeks. If you’ve had to post off a letter for Overpayment Relief, it’ll likely take longer. HMRC doesn’t just wave those through. They check them thoroughly, so it could be 10 or even 12 weeks before that balance actually hits your account. You can also use the HMRC “Check when you can expect a reply” tool for updated estimates.
The Bottom Line
Reclaiming tax you’ve overpaid is not some rare thing. It happens with many. And if you don’t check, that money just sits there. Therefore, in order to reclaim overpaid corporation tax in the UK, you need to act. Amend the return if you can. Also, keep an eye on deadlines.
How Accotax Can Help
If you need help to reclaim overpaid corporation tax UK or require expert assistance with any other accounting service, such as bookkeeping, VAT, or year-end accounts, visit Accotax. We offer a range of packages designed to fit your unique needs!
Reach out, get an instant quote, and let us help you stay compliant!
Disclaimer: The information about “How to Reclaim Overpaid Corporation Tax in UK” provided in this article including text and graphics. It does not intend to disregard any of the professional advice.
