What happens if you miss the Self Assessment deadline?

You get an automatic £100 penalty the moment the deadline passes, even if you owe no tax or are due a refund. If the return is still not filed after three months, daily penalties of £10 begin, up to £900. At six and twelve months there are further penalties of £300 or 5% of the tax due, whichever is higher. On top of the filing penalties, late payment of tax brings its own penalties and interest. The single best thing you can do is file as soon as possible, because the daily fines stop the day your return is in.

The starting fine is £100, charged automatically. After three months it can rise by £10 a day up to £900, and at six and twelve months a further £300 (or 5% of the tax owed if higher) is added each time. So a return left unfiled for a year can attract well over £1,600 in filing penalties alone, before any late-payment penalties and interest on the tax itself. The figures are the same whether or not you actually owe tax.

No. There is no grace period and the £100 penalty is automatic the moment the deadline passes. HMRC does not waive it for being a day or two late. The only way to avoid it is to file on time, or to successfully appeal on the basis of a genuine reasonable excuse. If you know you are going to be late, filing as quickly as possible still limits the damage by stopping the later penalties.

Yes. You can appeal a late filing penalty if you have a reasonable excuse, which HMRC takes to mean something genuinely outside your control, for example a serious illness, a bereavement, or a major technical failure when filing. Simply forgetting, or finding the return too difficult, is not usually accepted. You normally appeal within 30 days of the penalty notice, and you still need to file the outstanding return. We can help you decide whether an appeal is likely to succeed and put it together.

Do not let it stop you filing, the return and the payment are separate, and filing late makes things worse. File on time, then if you cannot pay in full you can set up a Time to Pay arrangement with HMRC to spread the bill into monthly instalments. Interest still applies, but it avoids the worst of the late-payment penalties and the stress. Paying as much as you can up front reduces the interest that builds on the rest.

For an online return the deadline is 31 January following the end of the tax year, and that is also the date your tax is due. Paper returns are due earlier, by 31 October. If you are newly self-employed you also need to register by 5 October in your second tax year. Missing any of these triggers penalties, which is why we track every client deadline and file in good time rather than at the last minute.