Self Assessment Tax Return 2026/27 — Deadlines, What to Include & How to File
A plain-English guide to completing your HMRC Self Assessment return — who files, key dates, payments on account and how to avoid penalties
📅 Updated May 2026🇬🇧 UK-specific⏱ 12 min read✅ 2026/27 tax year
Who needs to file a Self Assessment tax return
HMRC requires you to file a Self Assessment return if any of the following apply in a tax year:
You are self-employed as a sole trader and your gross income from the business is over £1,000
You are a partner in a business partnership
You are a company director (unless you have only PAYE income and no other untaxed income)
You have rental income above £2,500 after allowable expenses
Your total income is over £100,000 — even if all of it was taxed through PAYE
You have untaxed income of more than £2,500 (from savings interest, dividends above your allowance, etc.)
You or your partner earn above £60,000 and one of you receives Child Benefit
You have capital gains above the Annual Exempt Amount (£3,000 for 2026/27)
You are claiming certain tax reliefs (Gift Aid higher-rate relief, pension contributions, etc.)
HMRC notice to file
If HMRC sends you a notice to file a Self Assessment return, you must submit one even if no tax is owed and you do not meet any of the criteria above. Ignoring a notice will result in automatic late-filing penalties. If you believe a notice was sent in error, contact HMRC to have it withdrawn.
If you are no longer self-employed and do not need to file, you must actively deregister from Self Assessment — HMRC will not stop automatically.
How to register for Self Assessment
Register online through HMRC's website using Government Gateway. Use the 'register as self-employed' service if this is your first year. HMRC will:
Assign you a Unique Taxpayer Reference (UTR) — a 10-digit number that identifies you to HMRC. It arrives by post within 10 working days.
Set up your Government Gateway account for online filing.
Send you activation codes for online Self Assessment access.
Registration deadline: 5 October
You must register by 5 October after the end of the tax year in which you became self-employed or started receiving income that requires a return. For the 2026/27 tax year (which ends 5 April 2027), the registration deadline is 5 October 2027. Registering late incurs a penalty.
If you were already registered for Self Assessment in a previous year, you do not need to re-register — your UTR remains the same and your Government Gateway login still works.
Key deadlines for the 2026/27 tax year
The 2026/27 tax year runs from 6 April 2026 to 5 April 2027. Here are the critical dates after that:
5 Oct 2027
Registration deadline — register for Self Assessment if you were self-employed in 2026/27 for the first time.
31 Oct 2027
Paper return deadline — if filing a paper SA100, it must reach HMRC by this date.
31 Jan 2028
Online return deadline + tax payment — file your online return AND pay any tax owed for 2026/27. Your first payment on account for 2027/28 is also due on this date.
31 Jul 2028
Second payment on account — second advance payment toward your 2027/28 tax bill (if applicable).
The January crunch
31 January is the busiest date in the Self Assessment calendar. It combines three obligations: filing the online return, paying any balance owed for the previous year, and making the first payment on account for the current year. In a high-earning first year, this can mean paying up to 150% of a year's tax in a single month.
What to include in your Self Assessment return
The SA100 is the main return form. Most people complete it online through HMRC or tax software, which prompts you to add supplementary pages for each income source.
Self-employment income (SA103)
Complete the self-employment supplementary pages with:
Total turnover (gross business income before expenses)
Allowable business expenses — listed by category or as a total
Net trading profit
Capital allowances claimed (Annual Investment Allowance, etc.)
Losses brought forward or carried back
Employment income (SA102)
If you also had PAYE employment, enter gross pay and tax deducted from your P60. HMRC uses this to check no tax was underpaid through PAYE, and to ensure the correct rate band is applied to any self-employment income on top.
Other income sources to declare
UK property income (SA105) — rental income, holiday lettings
Dividends — from investments or your own limited company above the £500 allowance
Savings interest — above your Personal Savings Allowance (£1,000 basic rate; £500 higher rate)
Capital gains (SA108) — from selling shares, property (other than main home), business assets
Pension income — state pension, private pension lump sums
Foreign income (SA106) — overseas employment, rental or investment income
CIS deductions suffered — entered as tax already paid, offset against your bill
Reliefs and allowances to claim
Pension contributions to registered schemes (to claim higher-rate relief if not already given)
Gift Aid donations (to claim higher-rate relief on charitable giving)
Marriage Allowance (if your spouse earns below the Personal Allowance)
Blind Person's Allowance
Enterprise Investment Scheme (EIS) or Seed EIS relief
Payments on account
Payments on account are HMRC's way of collecting tax in advance for the following year, so you are not paying 12+ months' worth of tax in a single lump sum every January.
They apply if your Self Assessment tax bill is above £1,000 and less than 80% of your total tax was collected at source (through PAYE, CIS deductions, etc.).
Each payment on account is 50% of your current year's bill:
First payment on account — due 31 January, same day as the return
Second payment on account — due 31 July
Balancing payment — due the following 31 January, after filing the next return
How payments on account stack up — Year 1 vs Year 2
2026/27 tax bill: £4,000 (first year above threshold)
31 January 2028: Pay £4,000 (2026/27 bill) + £2,000 (first payment on account for 2027/28) = £6,000
31 July 2028: Pay £2,000 (second payment on account for 2027/28)
2027/28 actual bill: £4,500
31 January 2029: Pay £500 balancing payment + £2,250 (first PoA for 2028/29)
Cash flow implication:
In the first year your SA bill exceeds £1,000, you pay 150% of one year's tax in January. Budget carefully — set aside 25–30% of income throughout the year in a separate savings account to cover both the January bill and the payments on account.
Reducing your payments on account
If you know your next year's profits will be lower (for example, you have taken on fewer clients or worked fewer months), you can apply to reduce payments on account. Submit form SA303 online through your Government Gateway account, or call HMRC. HMRC will adjust the amounts.
Reduce with caution
If you reduce payments on account and your actual bill turns out to be higher than estimated, HMRC will charge interest on the underpayment from the date each payment was due. Only reduce if you have a well-founded reason to expect lower profits — not simply to delay payment.
Worked example — first year of significant self-employment
31 January 2028 payment due:
£6,742 (2026/27 bill) + £3,371 (first payment on account for 2027/28) = £10,113
Plus 31 July 2028: £3,371 (second payment on account)
Priya should set aside approximately £1,400/month throughout the year to cover these obligations.
CIS subcontractors and Self Assessment
If you work in construction under the Construction Industry Scheme (CIS), your contractors deduct tax from your payments before handing it over. These CIS deductions are entered on your Self Assessment return as tax already paid, and HMRC offsets them against your income tax and Class 4 NI bill.
To include CIS deductions:
Collect all your CIS deduction statements from contractors (they must issue these monthly).
Total up all CIS deductions for the tax year.
Enter the total in the "Construction Industry Scheme deductions" box on the SA103 self-employment pages.
HMRC automatically deducts this from the tax owed — any excess is refunded.
If your CIS deductions exceed your total tax liability for the year — common for lower-earning subcontractors — HMRC will issue a refund, typically within a few weeks of filing. Use our CIS tax calculator to estimate whether you are likely to owe more or get a refund before filing.
How to reduce your Self Assessment bill
There are legitimate ways to reduce the tax owed on your return. The most effective are:
Claim all allowable expenses — see the full expenses guide to make sure you are not leaving deductions on the table.
Make pension contributions — contributions to a SIPP or personal pension reduce your adjusted net income. Paying into a pension before 5 April each year reduces your SA bill for that year.
Gift Aid donations — if you are a higher-rate taxpayer, declaring Gift Aid donations on your return gives you additional relief at 40%.
Marriage Allowance — if your spouse earns less than £12,570 and you are a basic-rate taxpayer, you can transfer up to £1,260 of their Personal Allowance to you, saving up to £252 per year.
Timing large expenses — buying equipment or making pension contributions before 5 April rather than after can move a deduction into the current tax year.
The £100 penalty applies even if no tax is owed
HMRC charges the £100 late-filing penalty regardless of whether you owe any tax. Filing a nil return on time costs nothing. Filing it even one day late costs £100. Always file on time — even if you cannot pay, file first and then arrange a Time to Pay agreement with HMRC.
You must file if you are self-employed with income above £1,000, a company director, earning rental income above £2,500, have income above £100,000, have untaxed income above £2,500, claim Child Benefit with income over £60,000, or have capital gains above the annual exempt amount. You must also file if HMRC sends you a notice to file.
What is the Self Assessment filing deadline?
Online: 31 January following the end of the tax year. For 2026/27, that is 31 January 2028. Paper: 31 October 2027. Tax owed is also due on 31 January. If your bill exceeds £1,000, your first payment on account for the following year is also due on 31 January.
What are payments on account?
Advance payments toward next year's tax bill, required when your current bill exceeds £1,000. Each payment is 50% of the current bill. The first is due 31 January (same day as the return), the second on 31 July. In your first high-earning year you may owe 150% of a year's tax in a single January.
What happens if I file my Self Assessment return late?
£100 automatic penalty immediately after the deadline, even if no tax is owed. A further £10/day from 3 months late (up to £900). Then £300 or 5% of tax owed at 6 months and 12 months. Late payment also incurs interest (~7.25%/year) and 5% surcharges at 30 days, 6 months and 12 months.
Can I reduce my payments on account?
Yes, using form SA303 through your Government Gateway account, if you know next year's profits will be lower. If you reduce them too much, HMRC charges interest on the shortfall — only reduce if you are confident the liability will be genuinely lower.
What income do I need to declare on Self Assessment?
All income sources: self-employment profits, employment income not fully taxed at source, rental income, dividends above the £500 allowance, savings interest above the Personal Savings Allowance, pension income, overseas income, capital gains above £3,000, and CIS deductions suffered (entered as tax paid).
How do I register for Self Assessment?
Register online through HMRC's Government Gateway using the 'register as self-employed' service. HMRC will post you a Unique Taxpayer Reference (UTR) within 10 working days. You must register by 5 October after the end of the tax year in which you became self-employed.
What is the trading allowance?
£1,000 per year. If total self-employment income is £1,000 or less, you do not need to declare it. If above £1,000, you can claim the £1,000 allowance instead of actual expenses — but most traders with real expenses will be better off claiming actuals.