When was my Corporation Tax actually due?
For most small companies, your Corporation Tax is due 9 months and 1 day after the end of your accounting period. Your accounting period is usually the year your accounts cover. So if your year ended on 31 March, the tax is due by 1 January the next year.
That date matters because it's the line HMRC measures "late" from. Pay on or before it and you owe no interest. Pay even a day after it and the clock starts.
What does HMRC charge me for paying late?
HMRC charges interest on the tax you still owe. It isn't a one-off fine. It's a daily charge that keeps growing for as long as the bill is unpaid, so the longer you leave it, the more it costs.
The interest starts the day after your due date and runs until the day you pay the tax off in full. Clear the bill quickly and the interest stays small. Leave it for months and it adds up.
How much is the interest right now?
The rate is 7.75% a year (this is the figure from 9 January 2026).
This rate isn't fixed forever. It follows the Bank of England base rate, so when the base rate goes up or down, this rate moves with it. That's why you should always check the rate for the day you're paying rather than trust an old number. We use the current rate when we show you the figures.
A real example, in pounds
Say your company owes £10,000 in Corporation Tax, and you pay it 3 months late.
- The interest rate is 7.75% a year.
- Three months is a quarter of a year, so you pay roughly a quarter of that rate: about 1.94%.
- 1.94% of £10,000 is about £194.
So paying that £10,000 bill three months late costs you around £194 on top. Pay it six months late and you'd owe roughly £388. The bill itself never changes. The extra is purely the interest for being late.
(This is a rounded example to show how it works. The exact amount depends on the rate on each day and the precise number of days you're late.)
Isn't this the same as filing my return late?
No, and this trips a lot of people up. There are two separate things you have to do, and each has its own penalty if you're late:
- Paying the tax late means HMRC charges you interest (the thing this guide is about).
- Filing your Company Tax Return late means HMRC charges you a fixed penalty instead, starting at £200 and rising the longer you leave it.
You can be late on one and on time with the other. If you filed your return on time but paid the tax a month late, you only owe interest, no filing penalty. If you paid on time but sent the return in late, you owe the filing penalty, no interest. We cover the filing penalties in a separate guide.
I can't afford to pay it. What do I do?
Don't ignore it, that only grows the interest. If you can't pay the full amount, you can ask HMRC for a "Time to Pay" arrangement. That's an agreement to pay the bill off in instalments over a set period instead of all at once.
The sooner you ask, the better, ideally before the due date. You contact HMRC, explain what you can afford, and they set up a plan. Interest still runs on whatever is still owed while you pay it off, but a plan stops things getting worse and keeps you on the right side of HMRC.
How do I stop this happening again?
The simplest fix is knowing your due date well ahead of it and having the right figure ready. Most late payments happen because the director didn't know what was owed, or when. Work out the bill early, set the due date aside, and pay before it.
How SimpleReturns helps
When we prepare your return, we work out exactly what your Corporation Tax bill is and tell you the due date clearly, so the payment never sneaks up on you. You see the figure and the date before anything is filed. If you've already paid late and want to understand the interest, the current rate is built into how we explain your numbers.