Self Assessment is the system through which most UK individuals with untaxed income — the self-employed, landlords, higher earners, and those with significant investment income — calculate and pay their tax. The headline 31 January and 31 July dates have been the same for years, but Making Tax Digital for Income Tax went live on 6 April 2026, fundamentally changing the process for sole traders and landlords above the £50,000 threshold.
Payments on account are advance tax payments made twice a year (31 January and 31 July) towards the following tax year’s bill, each equal to half your previous year’s tax. They apply if your tax liability exceeds £1,000 and less than 80% was collected through PAYE. You can apply to reduce them via SA303 if you expect lower income — but underestimating triggers interest charges.
This guide explains the deadlines, payment mechanics, and what changes for the 2026/27 tax year and beyond.
📅 Key Deadlines at a Glance — 2025/26 Return
- Notify HMRC of new chargeability: 5 October 2026
- File paper return: 31 October 2026
- File online return: 31 January 2027
- Pay balancing payment + first 2026/27 POA: 31 January 2027
- Pay second 2026/27 payment on account: 31 July 2027
Who Has to File a Self Assessment Return?
You are typically required to file a return if any of the following apply:
- You were self-employed with gross income above £1,000
- You were a partner in a partnership
- You earned more than £150,000 from any source — the threshold above which HMRC routinely requires a return
- You received untaxed income — rental income, foreign income, or investment gains above the annual exempt amount
- You or your partner received Child Benefit and your income exceeded £80,000 (High Income Child Benefit Charge)
- You received tips, commission or other income not taxed at source
- HMRC has issued you with a notice to file
💡 Small Income? Check the Allowances First
The £1,000 trading allowance and £1,000 property allowance mean that small amounts of self-employment or rental income below £1,000 do not need to be reported at all. If gross income exceeds £1,000 but net profit is lower, you can elect to use the allowance instead of deducting actual expenses — sometimes eliminating the return requirement entirely.
Key Deadlines for the 2025/26 Return
The 2025/26 tax year ended on 5 April 2026. The relevant deadlines are:
| Action | Deadline |
|---|---|
| Notify HMRC of new chargeability for 2025/26 | 5 October 2026 |
| File a paper return for 2025/26 | 31 October 2026 |
| File an online return for 2025/26 | 31 January 2027 |
| Pay 2025/26 balancing payment + first 2026/27 POA | 31 January 2027 |
| Pay second 2026/27 payment on account | 31 July 2027 |
How Payments on Account Work
If your prior year's tax bill (after PAYE and other tax deducted at source) is more than £1,000, HMRC collects it through two payments on account — each equal to 50% of the prior year's bill.
🧮 Worked Example — 2025/26 Tax Year
- 31 January 2027: Balancing payment for 2025/26 plus first 2026/27 payment on account (50% of 2025/26 liability)
- 31 July 2027: Second 2026/27 payment on account (the other 50%)
- 31 January 2028: Balancing payment for 2026/27 plus first 2027/28 payment on account
Payments on account do not include Capital Gains Tax or the High Income Child Benefit Charge — those are settled in the balancing payment only.
⚠️ Reducing Payments on Account — Proceed With Care
If you expect your 2026/27 liability to be lower than 2025/26, you can apply to reduce your payments on account (SA303). But be careful: if you reduce them and your actual liability turns out higher, HMRC will charge interest on the shortfall from the original due dates. Only apply to reduce if you have a clear reason — a one-off gain, lower income or additional reliefs in the prior year.
Stop the Self Assessment Stress
We handle your annual return, payments on account and HMRC correspondence from £350/year.
Penalties and Interest in 2026/27
❌ Late Filing Penalties
- £100 — immediate penalty if the return is one day late
- £10 daily penalties from three months late, up to £900
- 5% of tax due (or £300 if greater) — at 6 months late
- Further 5% (or £300 if greater) — at 12 months late
HMRC interest on late paid tax tracks the Bank of England base rate plus 4%. For owners with cash flow flexibility, paying on time is almost always cheaper than financing the tax bill elsewhere.
Making Tax Digital for Income Tax — What Changed in April 2026
MTD for Income Tax (MTD ITSA) became mandatory from 6 April 2026 for sole traders and landlords with qualifying gross income above £50,000.
| MTD ITSA Threshold | Effective Date |
|---|---|
| Gross income above £50,000 | 6 April 2026 — NOW LIVE |
| Gross income above £30,000 | April 2027 |
| Gross income above £20,000 | April 2028 |
📋 If You Are In Scope — What You Must Do
- Keep digital records of all business income and expenses
- Submit quarterly updates through MTD-compatible software (April–June, July–September, October–December, January–March)
- Submit a final declaration (replacing the traditional SA return) by 31 January following the tax year end
- Paper records are no longer sufficient — every transaction must have a digital record
⚠️ Approaching the Threshold? Act Now
If your gross income is currently below £50,000 but you expect to cross it in 2026/27 or 2027/28, the time to move onto MTD-compatible software is before you become mandated — not after. Setting up mid-year on a new system while trying to file quarterly updates is significantly harder than starting fresh at the beginning of a tax year.
Capital Gains Tax — The 60-Day Reporting Rule
Disposals of UK residential property by UK residents must be reported and the CGT paid within 60 days of completion — separately from the annual Self Assessment return. Non-resident disposals of any UK land or property are also caught.
⚠️ Most-Missed Obligation in Self Assessment
The 60-day CGT rule is one of the most frequently missed obligations. Missing the deadline triggers automatic penalties starting at £100 — and many taxpayers don't realise the obligation exists until long after completion. Set a reminder on exchange of contracts, not completion day. Use our CGT calculator to estimate your liability before exchange.
✅ Key Takeaways — 2026/27
- Don't wait until January — file early to know your liability and plan cash flow, especially with payments on account due the same day
- Apply to reduce payments on account only if you genuinely expect a lower liability — guessing low triggers interest charges
- If you cross the £50,000 turnover threshold (or expect to in 2027/28), get onto MTD-compatible software now — before you become mandated
- Use the £1,000 trading and property allowances where they apply — small amounts of side income may not need reporting at all
- The 60-day CGT reporting rule on residential property is one of the most-missed obligations — set a reminder for exchange, not completion
- HMRC interest runs at base rate + 4% — paying late is expensive relative to most financing alternatives
Frequently Asked Questions
What are the Self Assessment deadlines for 2025/26?
Key deadlines for the 2025/26 return: notify HMRC by 5 October 2026, file paper return by 31 October 2026, file online by 31 January 2027, pay balancing payment plus first 2026/27 payment on account by 31 January 2027, pay second payment on account by 31 July 2027.
How do payments on account work?
If your prior year tax bill exceeds £1,000, HMRC collects it through two payments on account — each 50% of the prior year bill — due 31 January and 31 July. They don’t include Capital Gains Tax or the High Income Child Benefit Charge. You can apply to reduce them if you expect a lower liability, but under-paying triggers interest.
Who needs to use MTD for Income Tax from April 2026?
From 6 April 2026, MTD for Income Tax is mandatory for sole traders and landlords with qualifying gross income above £50,000. They must keep digital records and submit quarterly updates through MTD-compatible software, plus a final declaration by 31 January. The threshold drops to £30,000 from April 2027 and £20,000 from April 2028.
📚 Related reading
- Setting Up a UK Charity 2026 — If you’re giving substantially via Gift Aid, the Self Assessment higher-rate relief mechanics matter.
- Top 10 UK Business Tax Mistakes — Late filing and payments on account are two of the most common cash-flow surprises.
Shamim and the team at The Tax Lead prepare and file Self Assessment returns for individuals, landlords and the self-employed — including full MTD-compatible bookkeeping for those now in scope. Every return is reviewed by a qualified adviser.
Need help with your personal tax position?
For our broader Personal Tax service — Self Assessment, CGT 60-day reporting, residency planning, FIG regime, IHT — Chartered Tax Adviser-led, with same-working-day response on first contact.