When is the Self Assessment deadline 2026?

The Self Assessment online filing and payment deadline for the 2024-25 tax year is 31 January 2026, midnight. The paper-return deadline was 31 October 2025. The next first payment on account for 2025-26 is also due 31 January 2026.

What's the penalty for missing the Self Assessment deadline?

£100 automatic late-filing penalty even if no tax is due. After 3 months, £10/day for up to 90 days (£900). After 6 months, an extra £300 or 5% of tax due (whichever is higher). After 12 months, another £300 or 5%. Late payment also attracts interest (currently 7.75%) plus 5% penalties at 30 days, 6 months and 12 months.

Can I get an extension on the Self Assessment deadline?

HMRC doesn't grant deadline extensions for normal cases. You can appeal a late-filing penalty if you had a 'reasonable excuse' (serious illness, bereavement, technical failure on HMRC's side). File a TMA 70 appeal within 30 days of the penalty notice. If approved, the penalty is cancelled.

When are payments on account due?

Payments on account are due 31 January and 31 July each year. Each payment is 50% of your previous year's tax bill. They apply if your prior year's bill was over £1,000 and less than 80% of it was collected at source (e.g. through PAYE). You can reduce them via SA303 if you expect lower income.

Who needs to file a Self Assessment return?

You must file if any of these apply in the tax year: self-employed with income over £1,000, partner in a business partnership, rental income over £1,000, foreign income, capital gains over the £3,000 allowance, dividends over £500, savings interest over your Personal Savings Allowance, total income over £150,000, claiming foreign tax credit relief, or a company director taking salary plus dividends.

How do I file my Self Assessment online?

Register at gov.uk for Self Assessment if it's your first year (allow 10 working days for the UTR to arrive by post). Then sign into your HMRC online account, click 'Self Assessment', complete each section based on your records, submit, and pay. The whole process takes 30-60 minutes if your records are organised.

Self Assessment Deadline UK 2026: Every Date, Penalty and How to Avoid Them

The 2025-26 deadline calendar

Date	What's due	For tax year
5 October 2025	Register for Self Assessment if it's your first year	2024-25
31 October 2025	Paper Self Assessment return filing deadline	2024-25
30 December 2025	Online return deadline to pay via PAYE (tax under £3,000, employed)	2024-25
31 January 2026	Online return filing + tax payment + first payment on account	2024-25
5 April 2026	Tax year end	2025-26
31 July 2026	Second payment on account	2025-26
5 October 2026	Register for Self Assessment if it's your first year for 2025-26	2025-26
31 October 2026	Paper return filing deadline	2025-26
31 January 2027	Online filing + payment + first payment on account	2025-26

What happens if you miss the deadline

HMRC applies an automatic £100 penalty the moment you miss the 31 January online filing deadline, even if you owe no tax. From there the penalties stack quickly:

How late	Late filing penalty	Late payment penalty
1 day late	£100	Interest from 1 Feb
3 months late	+£10/day for next 90 days (up to £900)	Still interest only
6 months late	+£300 or 5% of tax owed (whichever higher)	5% of unpaid tax
12 months late	+£300 or 5% of tax owed (whichever higher)	Further 5% of unpaid tax

A return filed 12 months late with £5,000 of tax outstanding could end up costing £100 + £900 + (5% of £5,000 = £250) + (5% of £5,000 = £250) = £1,500 in filing penalties alone, plus £500 in late-payment penalties (5% + 5%), plus interest at 7.75%. Roughly £2,500 on top of the tax bill.

Late-payment interest in 2026

HMRC charges late-payment interest at Bank of England base rate plus 4 percentage points. As of mid-2026, base rate is 3.75%, so HMRC interest is 7.75%. The interest accrues daily from 1 February until you pay.

Interest you owe HMRC is not tax-deductible. If they owe you a refund, they pay interest at base rate minus 1 percentage point (currently 2.75%).

Reasonable excuses HMRC will accept

HMRC accepts a small set of "reasonable excuses" that can cancel a late-filing penalty:

You or a close relative had a serious illness or were in hospital around the deadline
A close relative died shortly before the deadline
HMRC's online service failed (verified outage)
You experienced a serious disaster (fire, flood) that destroyed your records
Postal disruption (Royal Mail strike) if you filed by post
Software issues that you reported promptly to HMRC

HMRC explicitly does not accept:

You forgot
You were too busy
You found the form too difficult
You didn't get a reminder (you don't have to receive one to be liable)
Your accountant let you down (you remain responsible)

To appeal, file an SA370 form within 30 days of the penalty notice. Set out the excuse, what you did about it, and when you filed the return. If your excuse meets the criteria HMRC will normally cancel the penalty.

Payments on account explained

Payments on account are advance payments toward next year's tax bill. They apply if your prior year's bill was more than £1,000 and less than 80% of it was collected at source (e.g. through PAYE).

Each payment is 50% of last year's bill, due on 31 January and 31 July. Your final balancing payment for the year (positive or negative) is settled the following 31 January.

Example. 2024-25 bill: £4,000. You pay £4,000 by 31 January 2026 (the balance). You also pay £2,000 (50% of £4,000) by 31 January 2026 as the first payment on account for 2025-26, and another £2,000 by 31 July 2026. Total leaving your account by 31 January 2026: £6,000.

If you expect your 2025-26 income to be lower (you've left self-employment, or your business has shrunk), you can apply to reduce payments on account via SA303 on your personal tax account. HMRC charges interest if you reduce too aggressively and end up underpaying.

Who has to file Self Assessment

You must file if any of these applied during the tax year:

You were self-employed (sole trader) with gross income over £1,000
You were a partner in a business partnership
You earned over £150,000 in total income
You received untaxed savings, investment or rental income over your allowances
You received dividends over £500
You realised capital gains above the £3,000 annual exempt amount
You earned foreign income or claimed foreign tax credit relief
You're a company director taking salary plus dividends
You earned over £50,000 and received Child Benefit (High Income Child Benefit Charge)

If none of these apply, you don't need to file. PAYE handles most employees' tax automatically. If HMRC sends you a return and you don't think you need to file, you can ask them to withdraw it before the deadline.

How to file online step by step

Register for Self Assessment at gov.uk if it's your first time. HMRC posts your Unique Taxpayer Reference (UTR) within 10 working days. Allow extra time, don't wait until late January.
Sign in to your HMRC online account using Government Gateway. From the dashboard, click "Complete your tax return".
Tailor your return, the system asks a few yes/no questions to show only the sections you need.
Complete each section, employment, self-employment, property, savings, dividends, capital gains, foreign income, expenses, reliefs. Refer to P60s, P45s, P11Ds, bank statements, broker statements, accounts.
Review, the calculation shows tax owed (or refund due) including any payments on account.
Submit and pay, you can pay by bank transfer, Direct Debit, debit card, or Faster Payments. Save your submission receipt and reference number.

The whole filing takes 30 minutes to a couple of hours depending on complexity. Pulling the records together is usually longer than the filing itself.