Full 2025/26 Tax Year Timeline
Estimate your Self Assessment tax bill before you file.
Use the UK Income Tax Calculator →Understanding Payments on Account
If your last Self Assessment bill was over £1,000, and less than 80% of your tax was already collected at source (e.g., through PAYE), HMRC requires you to make Payments on Account — advance instalments toward next year's tax bill, based on the assumption that you'll owe roughly the same amount again.
Each payment equals half of your previous year's tax bill, due on 31 January and 31 July. If your actual liability for the new year turns out to be higher, you pay a "balancing payment" the following 31 January. If it's lower — say your income dropped — you can apply to reduce your Payments on Account rather than overpaying and waiting for a refund.
Worked example
If your 2025/26 tax bill is £4,000, you'd typically pay: £4,000 (the 2025/26 balance) + £2,000 (first Payment on Account for 2026/27) = £6,000 on 31 January 2027, then a further £2,000 (second Payment on Account) on 31 July 2027.
Penalties for Filing Late
| How Late | Penalty |
|---|---|
| 1 day late | £100 fixed penalty — applies even if you owe no tax or are due a refund |
| 3 months late | £10 per day, up to a maximum of £900 (on top of the £100) |
| 6 months late | Greater of £300 or 5% of the tax due |
| 12 months late | A further £300 or 5% of tax due — in serious cases, up to 100% of the tax owed |
These penalties stack — someone six months late could already be facing over £1,300 in fixed penalties alone, before any interest on unpaid tax is added.
Interest and late payment penalties are separate
Beyond the filing penalties above, HMRC also charges daily interest on any unpaid tax from the original due date, plus separate late payment penalties (typically 5% of unpaid tax) at 30 days, 6 months, and 12 months if the tax itself remains unpaid — regardless of whether you filed on time.
Struggling to Pay? Time to Pay Exists
If you owe £30,000 or less and can clear it within 12 months, HMRC's online "Time to Pay" service lets you set up a payment plan yourself, without needing to call HMRC directly — a genuinely useful option if a big Self Assessment bill catches you short.
Frequently Asked Questions
Deadlines shift to the next business day when they fall on a weekend. Always confirm current dates on GOV.UK / HMRC before relying on them.