How do I file a Self Assessment tax return for the first time?

Register with HMRC, wait for your 10-digit UTR, set up your online sign-in, then file your 2025-26 return online by 31 January 2027 and pay any tax owed by the same date.

If you started as a sole trader or began letting a property between 6 April 2025 and 5 April 2026, your first Self Assessment return covers that tax year. This page follows GOV.UK as checked on 16 October 2026.

The dates for a first 2025-26 return

If you missed 5 October 2026

Register now on GOV.UK's Register for Self Assessment page, which sends you down the right route. GOV.UK says that if you tell HMRC after 5 October 2026 you could get a penalty. HMRC then sends a letter or email with a different filing deadline, 3 months from its date.

The payment date does not move. You must still pay by 11:59pm on 31 January 2027. If you registered late and do not pay all of the bill by then, you may get a failure to notify penalty, based on the amount still left to pay.

Your UTR and your online sign-in

After you register, HMRC sends your Unique Taxpayer Reference (UTR) by post, usually around 15 days later, and longer if you live overseas. It is a 10-digit number. You can also find it in your personal tax account or the HMRC app.

To file online you sign in to HMRC online services. If you have no sign-in details, you can create them, with either a Government Gateway user ID or GOV.UK One Login. You will be told when you sign in if you need to prove your identity. If you registered once before, reactivate that account first, or your return may be delayed.

What the return asks for

The main return is the SA100. On top of it, you fill in supplementary pages for each kind of income:

• Self-employment pages. These record self-employment income. The short version (SA103S) is for simpler affairs with turnover below the VAT threshold.
• UK property pages (SA105). These cover rent and other income from UK property.
• Other income. Wages from a job go on the employment pages (SA102), and there are other pages for things like foreign income and capital gains.

Online, you can save your entry and come back later. If a figure is not final, you can use a provisional figure, tell HMRC, and update it later. You have 12 months from the deadline to make corrections.

Over-deducted CIS is claimed back through your tax return. The sooner after 5 April you file, the sooner HMRC can repay you.

Records you need

GOV.UK says to keep records of all sales and income, all business expenses and your personal income. The proof includes receipts, bank statements and sales invoices. If you let property, GOV.UK says to keep records of all rent you get and the allowable expenses you pay, with rent books, receipts, invoices and bank statements. Allowable expenses include letting agents' fees and buildings insurance.

Keep the records for at least 5 years after the 31 January deadline. For a 2025-26 return filed by 31 January 2027, that means until at least the end of January 2032.

Paying the bill

Pay what you owe by 31 January 2027. Same or next day methods include online or telephone banking and a debit card online. A first Direct Debit takes 5 working days. If you cannot pay in full, GOV.UK points to weekly or monthly payments and help with paying.

Payments on account apply unless your bill was under £1,000, or more than 80% of the tax was paid outside Self Assessment. Each is usually half of the previous year's bill, so your first two are each half of your 2025-26 bill. In GOV.UK's example, a £3,000 bill with no earlier payments on account means paying £4,500 by 31 January, then £1,500 by 31 July. Our guide to payments on account explains more.

If you file or pay late

Your 2025-26 return is under the current penalties:

• £100 as soon as the return is late
• after 3 months, £10 a day, up to £900
• after 6 months, 5% of the tax due or £300, whichever is greater
• after 12 months, another 5% or £300, whichever is greater

Late payment brings 5% of the unpaid tax at 30 days, 6 months and 12 months, plus interest. With a reasonable excuse, you can appeal. GOV.UK says that from April 2027 new penalties apply to everyone who submits a personal Self Assessment return.

What this means for you

Your first return also decides your Making Tax Digital (MTD) date. Qualifying income is your self-employment and property income added together, before expenses. If it was over £30,000 in 2025-26, MTD starts for you on 6 April 2027, with four updates a year and the first due by 7 August 2027. Over £20,000 in 2026-27 means 6 April 2028.

If you started part-way through the year, HMRC scales a sole trader's income up to a full year if it has the information. Landlords must scale property income up themselves. To sign up for MTD you must be registered and have sent a return in the last 2 years, so this first return comes first.

Steps to file your first return

1. Register for Self Assessment now if you have not already.
2. Wait for your UTR by post, then keep it safe.
3. Set up your HMRC online sign-in and prove your identity if asked.
4. Gather your 2025-26 income, costs, rent, CIS statements and any other income.
5. Complete the return with the self-employment pages, the property pages, or both.
6. Check your bill and whether payments on account apply.
7. Submit and pay by 31 January 2027, earlier if you can.
8. Run the free MTD check to see if MTD starts for you in April 2027.

There are guides for the trades and for landlords. Our tax plans start once our HMRC registrations are complete. Until then you can join the waitlist, and no payment is taken.