Who has to file a UK Self Assessment tax return?

You must file if any of these apply: self-employed earning over £1,000, partner in a partnership, rental income above £2,500 (£10,000+ in some scenarios), savings/investment income above PA + PSA, foreign income, capital gains above £3,000 AEA, total income above £150,000, HICBC charge owed, or HMRC has sent you a notice to file. Check the gov.uk tool: gov.uk/check-if-you-need-tax-return.

When are Self Assessment deadlines for 2026/27?

Registration: by 5 October 2027 (6 months after tax year end). Paper return: 31 October 2027. Online return: 31 January 2028. Balancing payment: 31 January 2028. First Payment on Account 2027/28: 31 January 2028. Second Payment on Account: 31 July 2028. Late filing penalty: £100 immediately at 31 January 2028, more after.

How do Payments on Account work?

If your Self Assessment bill exceeds £1,000, HMRC requires Payments on Account toward next year. Each POA = 50% of current year tax bill. Paid 31 January (balance + POA1) and 31 July (POA2). New self-employed get hit hardest in year 2 - £5,000 bill in year 1 becomes £7,500 cash demand on 31 January year 2 (£5k balance + £2.5k POA1). Set aside ~40% of profit from start.

What if I can't pay my Self Assessment bill?

Apply for Time to Pay arrangement at gov.uk/difficulties-paying-hmrc. Online self-service for debts under £30,000 - spreads payments over 12 months. Interest accrues at 7.5% (HMRC current rate June 2026) but no late-payment penalty if arrangement set up before bill due. Above £30,000 requires phone call to HMRC Time to Pay team.

Making Tax Digital for Income Tax Self Assessment - phased in from April 2026 for sole traders + landlords with combined gross income above £50,000. Requires quarterly digital updates via approved software + final declaration. Phase 2 from April 2027 captures £30,000-£50,000 group. Below £30,000 remain on annual Self Assessment. Software: Xero, FreeAgent, QuickBooks, Sage are HMRC-recognised.

What expenses can I claim against self-employed income?

Wholly + exclusively business expenses: business mileage (£0.45/mi first 10k, £0.25 after), home office (simplified £10-£26/month or actual %), business phone usage, professional subscriptions, software, training in current trade, business insurance, accountancy fees. See our allowable expenses guide .

What's the late filing penalty?

Online return late: £100 fixed penalty immediately after 31 January (even if no tax due). After 3 months: £10/day up to 90 days max £900. After 6 months: greater of £300 or 5% of tax due. After 12 months: another £300 or 5%. Penalties stack - 12-month-late filer with £5,000 tax owes £100 + £900 + £300 + £300 = £1,600 in penalties on top of tax + interest.

Can I file my own Self Assessment or do I need an accountant?

Most PAYE-with-side-income or simple self-employed filers can DIY. Accountant worth it when: profits above £80k, multiple income streams, capital gains, rental property, complex business expenses, IR35 contractor. Typical accountant fee £200-£600 for individual SA, £400-£1,200 for sole trader full bookkeeping + SA, £800-£2,000 for Ltd company.

How do I register for Self Assessment?

Go to gov.uk/register-for-self-assessment. Pick correct form: self-employed (SA1), partner (SA401), other reason (SA1). Need Government Gateway account. HMRC sends Unique Taxpayer Reference (UTR) within 10 days. Use UTR + Government Gateway to file online. Register before 5 October following the tax year - so 5 October 2027 for 2026/27 income.

Practical guide

UK Self Assessment Filing Complete Walkthrough 2026/27

Step-by-step guide to UK Self Assessment 2026/27 - who needs to file, registration process, key deadlines, tax return sections explained, Payments on Account mechanics, and MTD ITSA changes from April 2026.

Do you need to file Self Assessment 2026/27?

You must file if any of these apply:

Self-employed with profit above £1,000 (the trading allowance)
Partner in a partnership
Rental income above £2,500 (above £10,000 in some cases)
Untaxed savings/investment income above your PSA
Capital gains above £3,000 AEA
Total income above £150,000
HICBC owed (adjusted net income above £60,000 with Child Benefit claim)
HMRC has issued you a Notice to File
Foreign income/assets, trust income, ministers of religion, certain occupational categories

Key dates for 2026/27 tax year

Deadline	Action
5 October 2027	Register for Self Assessment (6 months after tax year end)
31 October 2027	Paper return deadline
30 December 2027	Online return if you want tax collected via PAYE code (for amounts under £3,000)
31 January 2028	Online return + balancing payment + 1st Payment on Account 2027/28
31 July 2028	2nd Payment on Account 2027/28

The 6-step filing process

Register at gov.uk/register-for-self-assessment - HMRC sends UTR within 10 days
Gather documents: P60 from employer, P45 from previous jobs, P11D for BIK, bank interest statements, dividend vouchers, rental records, business books
Login at gov.uk/log-in-file-self-assessment with Government Gateway
Complete sections relevant to your income (employment, self-employment, property, capital gains, dividends, savings, foreign)
Submit the return - HMRC calculates tax owed
Pay by 31 January via Personal Tax Account, bank transfer, debit card, or Direct Debit

Payments on Account - the cash-flow trap

If your Self Assessment bill exceeds £1,000, HMRC requires Payments on Account toward the following year. Each POA equals 50% of current year tax bill. Year 2 hits hard:

Year 1 (2026/27) tax bill: £5,000 - paid 31 January 2028
Plus 1st POA 2027/28: £2,500 - same date
Total demand 31 January 2028: £7,500
Plus 2nd POA 2027/28: £2,500 - due 31 July 2028

Set aside approximately 30-40% of self-employed profit from day one.

MTD ITSA: changing from April 2026

Making Tax Digital for Income Tax Self Assessment phases in:

April 2026: Sole traders + landlords with combined gross income above £50,000
April 2027: Group above £30,000
Below £30,000: remain on annual Self Assessment

MTD ITSA requires: digital record-keeping via HMRC-recognised software (Xero, FreeAgent, QuickBooks, Sage, Coconut), quarterly updates to HMRC, end-of-period statement, final declaration. Annual Self Assessment paper or online return no longer accepted for affected groups.

Common Self Assessment mistakes

Missing the registration deadline (5 October following year end) - £100 penalty even if no tax due
Forgetting Payments on Account - hits year 2 with double tax demand
Not claiming all allowable expenses - typical sole trader leaves £1,000-£3,000/year unclaimed
Filing without records - HMRC investigations can demand evidence 5 years back
Late filing penalties stack - £100 + £900 + £300 + £300 = £1,600 for 12-month-late filer

Frequently asked questions

Who has to file a UK Self Assessment tax return?
You must file if any of these apply: self-employed earning over £1,000, partner in a partnership, rental income above £2,500 (£10,000+ in some scenarios), savings/investment income above PA + PSA, foreign income, capital gains above £3,000 AEA, total income above £150,000, HICBC charge owed, or HMRC has sent you a notice to file. Check the gov.uk tool: gov.uk/check-if-you-need-tax-return.
When are Self Assessment deadlines for 2026/27?
Registration: by 5 October 2027 (6 months after tax year end). Paper return: 31 October 2027. Online return: 31 January 2028. Balancing payment: 31 January 2028. First Payment on Account 2027/28: 31 January 2028. Second Payment on Account: 31 July 2028. Late filing penalty: £100 immediately at 31 January 2028, more after.
How do Payments on Account work?
If your Self Assessment bill exceeds £1,000, HMRC requires Payments on Account toward next year. Each POA = 50% of current year tax bill. Paid 31 January (balance + POA1) and 31 July (POA2). New self-employed get hit hardest in year 2 - £5,000 bill in year 1 becomes £7,500 cash demand on 31 January year 2 (£5k balance + £2.5k POA1). Set aside ~40% of profit from start.
What if I can't pay my Self Assessment bill?
Apply for Time to Pay arrangement at gov.uk/difficulties-paying-hmrc. Online self-service for debts under £30,000 - spreads payments over 12 months. Interest accrues at 7.5% (HMRC current rate June 2026) but no late-payment penalty if arrangement set up before bill due. Above £30,000 requires phone call to HMRC Time to Pay team.
What is MTD ITSA?
Making Tax Digital for Income Tax Self Assessment - phased in from April 2026 for sole traders + landlords with combined gross income above £50,000. Requires quarterly digital updates via approved software + final declaration. Phase 2 from April 2027 captures £30,000-£50,000 group. Below £30,000 remain on annual Self Assessment. Software: Xero, FreeAgent, QuickBooks, Sage are HMRC-recognised.
What expenses can I claim against self-employed income?
Wholly + exclusively business expenses: business mileage (£0.45/mi first 10k, £0.25 after), home office (simplified £10-£26/month or actual %), business phone usage, professional subscriptions, software, training in current trade, business insurance, accountancy fees. See our <a href="/uk-self-employed-allowable-expenses-master-2026-27-guide" class="underline">allowable expenses guide</a>.
What's the late filing penalty?
Online return late: £100 fixed penalty immediately after 31 January (even if no tax due). After 3 months: £10/day up to 90 days max £900. After 6 months: greater of £300 or 5% of tax due. After 12 months: another £300 or 5%. Penalties stack - 12-month-late filer with £5,000 tax owes £100 + £900 + £300 + £300 = £1,600 in penalties on top of tax + interest.
Can I file my own Self Assessment or do I need an accountant?
Most PAYE-with-side-income or simple self-employed filers can DIY. Accountant worth it when: profits above £80k, multiple income streams, capital gains, rental property, complex business expenses, IR35 contractor. Typical accountant fee £200-£600 for individual SA, £400-£1,200 for sole trader full bookkeeping + SA, £800-£2,000 for Ltd company.
How do I register for Self Assessment?
Go to gov.uk/register-for-self-assessment. Pick correct form: self-employed (SA1), partner (SA401), other reason (SA1). Need Government Gateway account. HMRC sends Unique Taxpayer Reference (UTR) within 10 days. Use UTR + Government Gateway to file online. Register before 5 October following the tax year - so 5 October 2027 for 2026/27 income.