Self Assessment Tax Return Calculator

If you are self-employed, a landlord, a company director, or earn over 150,000, you will likely need to file a Self Assessment tax return each year. The tax year runs from 6 April to 5 April the following year. You must register for Self Assessment by 5 October after the end of the tax year in which you first need to file. HMRC then issues you a Unique Taxpayer Reference (UTR) which you use for all future returns.

The deadline for online returns is 31 January following the end of the tax year. For the 2024/25 tax year, that means 31 January 2026. Paper returns have an earlier deadline of 31 October. Late filing incurs an automatic 100 penalty, even if you owe no tax. If you are more than three months late, daily penalties of 10 per day apply (up to 900). After six months, a further 300 or 5% of the tax due is charged, whichever is greater.

Payments on account are advance payments towards next year's tax bill. If your Self Assessment tax bill is over 1,000 and less than 80% was collected at source (via PAYE), HMRC requires two payments on account, each equal to half of the previous year's tax bill. These are due on 31 January and 31 July. Any remaining balance is settled with a balancing payment the following 31 January. If your income drops, you can apply to reduce your payments on account, but be aware that interest is charged if you reduce them too much.

Making Tax Digital (MTD) for Income Tax is being phased in from April 2026 for self-employed individuals and landlords with income over 50,000. This will require quarterly digital submissions via compatible software instead of an annual return. Those with income over 30,000 will follow from April 2027. Start using MTD-compatible software early to smooth the transition, as the annual return process you are used to will eventually be replaced entirely.