Tax deadlines

Missing a tax deadline is expensive and entirely avoidable. The Self Assessment calendar has just a handful of dates that matter — this guide lists them for the 2025/26 return, and explains the penalties so you never get caught out.

The key dates

• 5 October — register for Self Assessment if you became self-employed in the previous tax year
• 31 October — paper tax returns due (online is easier and more common)
• 31 January — online return due AND final balancing payment for the previous tax year due
• 31 July — first payment on account for the current tax year (half of last year’s bill)
• 31 January — second payment on account (the other half)

Payments on account

If your Self Assessment bill (not counting Class 2 NI and student loan repayments) is over £1,000, HMRC expects you to pay half of your tax bill in advance for the current year — half on 31 January and half on 31 July. It’s not extra tax; it’s pre-paying your expected bill so next January’s bill is only the difference.

Example. Your 2025/26 tax bill was £3,000. You pay £3,000 plus a £1,500 payment on account on 31 January 2027, another £1,500 on 31 July 2027, then the difference between your actual 2026/27 bill and the £3,000 already paid on 31 January 2028.

Penalties for missing dates

• Registering late — a fine, up to £100 for being late, with more if HMRC has to estimate your tax
• Filing late — £100 immediately after 31 January, then daily penalties of £10 a day after three months (up to 90 days), and percentage-based penalties for longer delays
• Paying late — 5% of the unpaid tax after 30 days, another 5% after 6 months, and another 5% after 12 months, plus interest

How to avoid the rush

• File as soon as you have your figures — you can file and pay separately
• Set reminders for 31 January and 31 July
• Keep your records organised during the year (see our bookkeeping guide)
• Use your accountancy software or accountant to calculate your bill in advance

If you can’t pay

HMRC operates Time to Pay — an arrangement to spread your bill into manageable instalments. Apply before the deadline where possible. Interest runs on late amounts, but having a plan in place stops automatic penalties escalating.

Stay on top of it

Use the self-employed tax calculator throughout the year to estimate your bill before the deadline hits, and keep the dates in this guide somewhere visible.