Self Assessment 2025-26 — complete filing guide

The 2025-26 UK tax year ran 6 Apr 2025 – 5 Apr 2026. SA returns are due 31 October 2026 on paper or 31 January 2027 online — that's also when your balancing payment and first Payment on Account for 2026-27 are due.

Your SA filing workflow

  1. 1

    Check whether you actually need to file

    Most PAYE-only employees don't file SA. You must file if you had self-employment income over £1,000, rental income over £2,500, CGT to pay, total income over £150,000, HICBC applies, untaxed dividends over £500, untaxed interest over £10,000, foreign income over £300, or HMRC sent you a notice.

    Self Assessment Checker — 10+ criteria
  2. 2

    Register for Self Assessment (get your UTR)

    New to SA? Register with HMRC by 5 October 2026 — you'll need a Unique Taxpayer Reference (UTR) and Government Gateway account. Sole traders register via SA1; self-employed via CWF1; partners via SA401. Allow 2-3 weeks for the UTR to arrive by post.

    Registration + Gateway walkthrough
  3. 3

    Gather your documents

    P60 / P45 / P11D, self-employment income & expense records, rental statements, dividend vouchers, interest certificates, CGT computations, pension contributions, Gift Aid receipts, student loan start balance, Child Benefit received (for HICBC), and any previous-year POA paid.

    Preview refund or balance owed
  4. 4

    Complete & submit online via HMRC Gateway

    Log in at gov.uk/log-in-file-self-assessment-tax-return. The main SA100 covers income tax; supplementary pages cover self-employment (SA103), property (SA105), CGT (SA108), foreign (SA106), partnership (SA104). Save often — HMRC lets you return later before submitting.

    What happens at each Gateway screen
  5. 5

    Pay balancing payment + Payments on Account

    By 31 Jan 2027: balancing payment for 2025-26 plus first POA for 2026-27 (50% of 2025-26 tax liability). Second POA due 31 Jul 2027. Claim a reduction (SA303) if your 2026-27 income will be lower. Late payment triggers 5% + 5% + 5% surcharges plus HMRC interest.

    Payment on Account Calculator

Key dates — 2025-26 filing cycle

Date Event Who
6 Apr 2025 2025-26 tax year starts All UK taxpayers
5 Apr 2026 2025-26 tax year ends All UK taxpayers
5 Oct 2026 Register for SA if new First-time SA filers
31 Oct 2026 Paper SA return deadline Paper filers
30 Dec 2026 Online deadline to have <£3,000 tax collected via PAYE code PAYE + small SA balance
31 Jan 2027 Online SA return + balancing payment + first POA All online filers
31 Jul 2027 Second POA for 2026-27 Anyone with POA liability

Full HMRC timetable: UK tax deadlines.

Common SA mistakes

  • Forgetting the £10,000 untaxed interest trigger

    Savings allowance £1k (basic) / £500 (higher) is about tax-free, not reporting. If your total untaxed interest is over £10,000, you must file SA regardless.

  • Missing 60-day CGT property reports

    UK residential property gains need a separate 60-day CGT-on-property return AND inclusion on the annual SA — not either/or.

  • Not claiming HICBC properly

    If your household ANI is £60k–£80k and you or partner receive Child Benefit, the High Income Child Benefit Charge applies. Still required even if your partner is the Child Benefit claimant.

  • Double-counting pension tax relief

    Relief-at-source pensions (most workplace & SIPPs) already claim basic-rate relief automatically. Only claim higher/additional rate relief on SA — don't claim the basic-rate element again.

  • Reducing POA too aggressively (SA303)

    If 2026-27 actual liability exceeds the reduced POA, HMRC charges interest back to the original due date — not just from when the shortfall was paid.

  • Missing Marriage Allowance transfer

    If one partner earns below PA (£12,570) and the other is basic-rate, the non-earner can transfer £1,260 of PA. Worth up to £252 — backdate up to 4 tax years.

Related: Late filing penalty relief → · Reducing your POA (SA303) →

Related tools for SA filers

SA Penalty Calculator

£100 + £10/day + 5% tiers

Self-Employment Tax

Class 2 & 4 NI + income tax

CGT 60-Day Reporting

Property gains disclosure

Capital Gains Tax

£3k AEA, 18/24% rates

Dividend Tax

£500 allowance, 8.75/33.75/39.35% (2025-26)

Rental Income Tax

Mortgage interest 20% credit

CIS Subbie Refund

20/30% deductions reconciled

MTD for ITSA Checker

April 2026 £50k threshold

Frequently asked questions

Who needs to file Self Assessment for 2025-26?

You must file if any applies during 6 Apr 2025 – 5 Apr 2026: self-employment income over £1,000, partnership, total taxable income over £150,000, rental income over £2,500, CGT to pay (gains over £3,000 AEA or proceeds over £50,000), HICBC (household ANI £60k+ with Child Benefit), untaxed dividends over £500, untaxed interest over £10,000, foreign income over £300, or HMRC sent a notice to file.

When is the Self Assessment 2025-26 deadline?

31 October 2026 for paper returns. 31 January 2027 for online returns — this is also when your balancing payment and first Payment on Account for 2026-27 are due. Second POA is due 31 July 2027.

What happens if I miss the 31 January 2027 deadline?

£100 immediate fixed penalty even with £0 owed. After 3 months: £10/day up to £900. After 6 months: £300 or 5% of tax owed (whichever is greater). After 12 months: same again. Balancing payment also triggers 5% surcharges at 30 days / 6 months / 12 months plus HMRC late-payment interest (7.75% from 9 January 2026 — Bank of England base rate + 4%, moves with the base rate).

Do I need to register for SA if this is my first year?

Yes — register with HMRC by 5 October 2026 for the 2025-26 year. Self-employed: form CWF1. Not self-employed (e.g. rental income, CGT): form SA1. Partners in a partnership: form SA401. HMRC posts your Unique Taxpayer Reference (UTR) — allow 2-3 weeks.

Can I amend my SA return after filing?

Yes. For 2025-26 you have until 31 January 2028 (12 months after the filing deadline) to amend online. After that, you need to write to HMRC explaining the error.

Do I need to file SA if I'm just a director?

Not automatically. Since 2018, HMRC officially states directors only need SA if they meet the standard criteria — untaxed dividends over £500, total income over £150k, etc. But in practice HMRC often still sends notices to directors; check whether you received SA316.

Is MTD for ITSA mandatory for 2025-26?

No. Making Tax Digital for Income Tax Self Assessment (MTD for ITSA) becomes mandatory from 6 April 2026 for self-employed and landlords with qualifying income over £50,000 (2026-27 year onwards). The 2025-26 return is filed under the legacy SA system.

Not sure where to start?

Run the Self Assessment Checker first — 30 seconds across 10+ HMRC criteria and you'll know if you need to file at all.

Start the Self Assessment Checker