Penalties are not a proportionate response to being a bit disorganised. A Self Assessment return filed a year late can cost £1,600 in penalties before a penny of the actual tax is considered. The rules are unforgiving in a way that catches people out repeatedly.
Self Assessment
The UK tax year runs from 6 April to 5 April. The return for that year is due the following January.
| What | When |
|---|---|
| Register for Self Assessment (first time) | 5 October |
| Paper return filing deadline | 31 October |
| Online return filing deadline | 31 January |
| Balancing payment for the year | 31 January |
| First payment on account | 31 January |
| Second payment on account | 31 July |
What being late costs
- Day one: £100, whether or not any tax is owed
- Three months: £10 a day for up to 90 days — a further £900
- Six months: 5% of the tax due, or £300, whichever is higher
- Twelve months: another 5% or £300
Late payment penalties sit on top of late filing penalties, and interest runs on the unpaid amount throughout.
If your bill exceeds £1,000 and most of your tax is not collected at source, HMRC asks for two advance instalments towards next year, each half of this year's bill. In your first year of self-employment that means roughly eighteen months of tax due within about six months. Plan for it in your first year, not your second.
Corporation tax and Companies House
Note the order here, because it surprises people: the tax is due before the return that calculates it.
| What | When |
|---|---|
| Pay corporation tax | 9 months + 1 day after period end |
| File the CT600 return | 12 months after period end |
| File accounts at Companies House | 9 months after the accounting reference date |
| First accounts after incorporation | 21 months after incorporation |
| Confirmation statement | Within 14 days of the review period ending |
Companies House late filing penalties
| How late | Penalty |
|---|---|
| Up to 1 month | £150 |
| 1 to 3 months | £375 |
| 3 to 6 months | £750 |
| More than 6 months | £1,500 |
File late in two consecutive years and the penalty doubles. Persistent failure to file is also grounds for the company to be struck off, and for directors to be disqualified.
HMRC applies its own separate penalties for a late CT600: £100 immediately, another £100 at three months, then 10% of the unpaid tax at six months and a further 10% at twelve.
VAT
Returns and payment are both due one calendar month and seven days after the end of each quarter. So a quarter ending 31 March is due by 7 May.
Late submission: penalty points
Since January 2023, late VAT returns work on a points system rather than an immediate fine. Each late submission earns one point. Reach the threshold for your filing frequency and you get a £200 penalty, plus another £200 for every late return after that while you remain at the threshold.
| Filing frequency | Points threshold |
|---|---|
| Annual | 2 |
| Quarterly | 4 |
| Monthly | 5 |
Late payment
Paying late is charged separately from filing late. For VAT due on or after 31 May 2025, the first penalty is 3% of the amount still outstanding at day 15, plus a further 3% of whatever is still outstanding at day 30. From day 31, a second penalty accrues daily at an annual rate of 10% until the balance is cleared. Interest runs alongside all of it.
Contacting HMRC and agreeing a Time to Pay arrangement before day 15 prevents the penalties from building. Silence is the expensive option.
Payroll and PAYE
| What | When |
|---|---|
| Full Payment Submission (RTI) | On or before each pay date |
| Pay PAYE and NI — electronically | 22nd of the following month |
| Pay PAYE and NI — by post | 19th of the following month |
| CIS monthly return | 19th of the following month |
| Issue P60s to employees | 31 May |
| File P11D and P11D(b) | 6 July |
| Pay Class 1A NI on benefits | 22 July |
If your average monthly PAYE liability is under £1,500, you can pay quarterly instead. Late CIS returns start at £100 and escalate quickly, which makes them one of the more expensive things to forget.
Two more worth diarising
- Capital gains on UK residential property: a separate return and payment within 60 days of completion. This one is missed constantly, because people assume it can wait for the annual return. It cannot.
- P11D and benefits in kind: if the company provides a car, private medical cover or an interest-free loan over £10,000, that is reportable each July.
What to actually do about it
Put every date that applies to you in a calendar with a reminder four weeks ahead, not one week. Four weeks is enough time to find missing records; one week is not.
And if you are already late — file anyway, today. Penalties stop growing from the date you file, and HMRC treats voluntary disclosure very differently from a failure it has to discover on its own.
Get in touch. There is a reasonable-excuse appeal route for some penalties, and it works considerably better when the return has already been filed. Tell us where you stand →
Deadlines and penalty rates were correct at the time of writing and can change at Budgets. This is general information rather than advice for your circumstances — check your own position with us or on GOV.UK before relying on it.