Self Assessment dates and payments on account
The first January after your first profitable year is the one that catches sole traders out: you can owe last year's tax and half of next year's on the same day.
Your key dates
- 1st payment on account31 January 2027
- 2nd payment on account31 July 2027
- Balancing payment31 January 2028
The online return itself is due by 31 January after the end of the tax year (5 April).
How payments on account work
If your Self Assessment bill is £1,000 or more and most of your tax isn't collected at source, HMRC asks you to prepay the next year in two instalments — each 50% of last year's bill — due 31 January and 31 July. Any shortfall is a balancing payment the following January.
Reducing a payment on account
If you know your profit has fallen, you can apply to reduce your payments on account. Be realistic: if you reduce them too far, HMRC charges interest on the difference.
Set money aside monthly
The calculator shows a monthly set-aside figure covering Income Tax and Class 4 NI. Moving that amount into a separate account each month is the simplest way to make January uneventful.
FAQ
- Why is my first January bill so large?
- It combines your first year's tax with the first payment on account for the next year — effectively 150% of one year's tax.
- What if I can't pay on time?
- Contact HMRC about a Time to Pay arrangement before the deadline. Late payment attracts interest and, after 30 days, penalties.
- Does Class 2 NI still apply?
- Compulsory Class 2 contributions were removed for most self-employed people; voluntary contributions can still be paid to protect your State Pension record.
Run your own numbers
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Estimates and general information only — not tax advice. Rules change; check with a qualified accountant before acting.