SA100 box by box: a walkthrough of the main tax return

The SA100 is the main Self Assessment tax return. It collects your personal details, asks which extra pages you need, records interest, dividends, pensions and reliefs, and ends with how you want any tax collected or repaid. For 2025-26 the paper deadline has passed, so you must file online by 31 January 2027.

What is the SA100 and who files it?

The SA100 is the core return that every Self Assessment taxpayer files, with supplementary pages added for things like self-employment or rental income. The 2026 form on GOV.UK’s SA100 page covers the tax year 6 April 2025 to 5 April 2026.

HMRC’s guide to the form is the SA150, “How to fill in your tax return”. GOV.UK updated it on 8 September 2026 with extra guidance on the employment pages for company directors.

Filing online uses the same questions in a different order. This walkthrough follows the paper form, so you can match boxes to the notes. Our guide on how to file a Self Assessment return covers the online steps.

Page TR1: your personal details

TR1 confirms who you are. You need your 10-digit Unique Taxpayer Reference (UTR) and your National Insurance number. Check your date of birth, address and phone number are current.

If you have lost your UTR, see how to find your UTR number.

Page TR2: which supplementary pages you need

TR2 is a list of yes or no questions. HMRC’s form says that if you put an X in any “Yes” box, you must also fill in the supplementary pages for that income or gain.

Choosing the right self-employment page is covered in SA103S or SA103F. Landlords should read our SA105 walkthrough.

Directors: new questions for 2025-26

Directors now have to give more detail on the employment pages. The Income Tax (Additional Information to be included in Returns) Regulations 2025 require directors of close companies to complete boxes 7.1 to 7.4 on the SA102:

• the company name (7.1) and registered number (7.2)
• the dividends received from the company (7.3), entering zero if none
• the highest percentage shareholding held in the year (7.4)

The ATT says HMRC’s view is that only one £60 penalty can arise per return for missing this information. Our page on Self Assessment for directors has more.

Page TR3: interest, dividends, pensions and benefits

TR3 is where most savers and pensioners enter their income. The UK interest and dividend boxes on the 2026 form are:

If your foreign interest or dividends are above those limits, or you want to claim foreign tax credit relief, use the SA106 foreign pages instead.

The next part of TR3 covers the State Pension, other pensions, taxable state benefits and other UK income. Enter the gross amounts and any tax taken off, using your P60 or pension statement.

Tax reliefs and charges

The pages after TR3 record reliefs that cut your bill and charges that add to it.

• Pension contributions. Payments to a personal pension under relief at source, and other contributions, so higher rate relief can be given.
• Gift Aid. Donations in the year, plus any you want to carry back to the previous year.
• Student and Postgraduate Loan repayments. Plan types and any amounts already deducted by an employer.
• High Income Child Benefit Charge. GOV.UK says the charge applies where income is over £60,000, at 1% of Child Benefit for every £200 above that. Full repayment is reached at £80,000.
• Marriage Allowance and Blind Person’s Allowance. Claims or transfers if they apply.

Finishing your return

The final pages deal with paying, repayment and signing.

1. Coding out. If you owe less than £3,000 and already pay tax through PAYE, HMRC can collect it through your tax code. You must file online by 30 December 2026. See paying through your tax code.
2. Repayments. Give bank details if HMRC owes you money.
3. Adviser details. Add your accountant’s details if they prepared the return.
4. Any other information. Use this space for estimates or explanations.
5. Declaration. Sign to confirm the return is correct and complete.

You can estimate your bill first with our Self Assessment calculator.

Key dates for the 2025-26 return

What to do now

Gather your P60, P11D, bank interest and dividend statements, and pension contribution records. Then work through TR2 first, so you know which supplementary pages to add before you start the figures.

Frequently asked questions

Can I still send a paper SA100 for 2025-26?

The paper deadline was 31 October 2026. GOV.UK advises filing online if you miss it, because the online deadline is 31 January 2027.

Where do UK dividends go on the SA100?

UK company dividends go in box 4 on page TR3. Other dividends go in box 5.

Do I need the foreign pages for a small amount of foreign interest?

Not always. Untaxed foreign interest up to £2,000 can go in box 3, and foreign dividends up to £500 in box 6, unless you are claiming foreign tax relief.

How do I pay my tax through my tax code?

You must owe less than £3,000, already pay tax through PAYE, and file online by 30 December 2026. You cannot make a part payment to get under the limit.

What new information do directors give for 2025-26?

Directors of close companies must give the company name and number, dividends received and their percentage shareholding in boxes 7.1 to 7.4 of the SA102.