Self Assessment — the tax return for self-employed, CIS subcontractors and anyone with income outside PAYE. You file it online through gov.uk: deadline 31 January, late filing means an automatic £100 penalty (even if you are due a refund). The process has 7 steps: UTR → Government Gateway → SA100 + the supplementary pages you need → check → submit. An accountant charges £150–400 for the same thing.
An accountant charges £150–£400 for the same thing. If you have one job, clear expenses and at least B1 English — you can do it. Deadline: 31 January 2027 for 2025/26.
Click on a step below to read the details. Or scroll — each step is explained in its own section.
P60, P45, CIS statements, банковские проценты, дивиденды, доход от аренды.
Если первая декларация — регистрация на gov.uk. ~15 рабочих дней по почте.
Заведите личный кабинет HMRC. Сохраните пароль офлайн — восстановление долгое.
Основная форма. Доходы, расходы, allowances. Online — проще, чем бумага.
SA103 для self-employed, SA105 для аренды, SA106 для иностранного дохода.
HMRC покажет итог: должны вы или вам. Сверьте с собственной таблицей.
Дедлайн online: 31 января. Бумажный: 31 октября. Штраф £100 за просрочку.
HMRC does not notify you automatically. The responsibility is yours. If you must file and you do not — penalties start.
Any self-employed person: CIS construction workers, Uber/Bolt, Deliveroo, cleaners, tutors, Vinted/eBay sellers.
Construction workers whose contractor withholds CIS deductions — SA is mandatory to reclaim any overpayment.
A share in any business partnership requires SA.
Rental income, dividends, foreign income, capital gains (CGT).
Whatever the source — PAYE alone is no longer enough.
Any income from abroad, including pension, rent, dividends.
One employer, correct tax code, no side income.
Covered by the trading allowance — SA not needed.
If covered by the Personal Savings Allowance (£1,000 basic rate) — SA not needed.
If you are filing for 2025/26 for the first time — register by 5 October 2026. This is the registration deadline, not the filing deadline.
UTR (Unique Taxpayer Reference) — a 10‑digit number. Without it you cannot log into Self Assessment. It arrives by letter to your registered address.
gov.uk/register-for-self-employment → “Register as self‑employed”. You will receive your UTR AND register for Class 2/4 NI at the same time.
Form CWF1 →For example, rental income or foreign income. Use form SA1 instead of CWF1.
Form SA1 →Many sources say “5–10 days” — that is wrong. HMRC sends the UTR by standard post. The real time is about 15 working days. If you have lived at your address for less than a year — the letter may get lost. Register early.
From 9 February 2026 HMRC is moving to GOV.UK One Login. New users create an account through One Login. Existing users — still through Gateway for now, the transition will be gradual.
If you already have a Government Gateway account — log in as usual. If not — create one through GOV.UK One Login.
Your NI number is mandatory. Plus one of: UK passport, BRP, or payslips from the last 3 months. Sometimes HMRC asks for extra confirmation by post — keep that in mind for your timing.
After logging in: Services → “Self Assessment” → “Activate”. You will need your UTR. Activation can take up to 24 hours.
SA100 is the main form. You add the supplementary pages you need. The choice depends on your sources of income.
Personal details, PAYE employment income (from your P60), savings interest, dividends, charitable giving. Mandatory for everyone.
For most sole traders with turnover < £85,000. CIS workers — also use this one.
Turnover > £85,000 or a complex expense structure.
Rental of UK property, including renting out a room.
Income from other countries: rent, dividends, salary, pension from abroad.
If you are non-domiciled or used the remittance basis. You should get advice from an accountant.
The main rule for expenses: “wholly and exclusively” — only for business, nothing personal. HMRC checks.
In form SA103S there is a special field “CIS deductions suffered”. Enter the EXACT amount from all your CIS statements for the year — not an estimate.
HMRC matches your figure against the data from contractors. A mismatch → delay or refusal.
The contractor must give you a statement within 14 days after the end of the tax month. If they do not — that is a breach. Send a written request, and if necessary complain to HMRC.
After you submit, the SA302 appears in your account within 72 hours — not immediately. If you need the SA302 for a mortgage, do not leave the submission until the last day.
After you submit your return, the SA302 (tax calculation) appears in your HMRC online account only after 72 hours. If you are getting a mortgage and need the SA302 — file your SA well in advance, not on the day of your mortgage adviser meeting.
Gross income = total of all P60s, P45s, CIS statements. Expenses = only real ones, with documents. NI number accurate.
HMRC shows the final amount before you submit. If the figure is unexpectedly large — recalculate your expenses. Do not submit without checking.
For a refund — sort code + account number of a UK account. BACS transfer is faster than a cheque.
After you submit, HMRC gives you a reference number. Save a screenshot or PDF. This is your proof of filing.
HMRC does not remind you. A £100 penalty arrives on the day you are late — even if you are due a refund. Penalties for late filing and late payment are separate.
These are two independent penalties. You can file on time but pay late — then you will only get the late payment penalty (5% of the tax at 30 days, 6 months and 12 months overdue). You cannot “save” on filing if you do not have the money to pay.
If you are self-employed or a landlord with income > £50,000 — from 6 April 2026 you must keep digital records and submit quarterly updates through MTD-compatible software. This changes the rules completely: one annual SA return is no longer enough. The threshold > £30,000 will apply from April 2027.
Compatible software on gov.uk →Filling in SA without documents is a risk of mistakes. Collect everything in advance, take photos and keep them for at least 5 years (HMRC requirement).