About Self Assessment Helper

A free, independent helper for people who are employed and also have some rental or self-employed income, and need to do a Self Assessment return.

What it is, and isn't

• It's guidance. It turns your answers into the figures for each box and estimates your bill using 2025-26 rates.
• It's not financial or tax advice, and it isn't regulated. It can't know everything about your situation.
• It's not HMRC or GOV.UK and has no connection with them.
• It doesn't file anything. You sign in to GOV.UK yourself, enter the figures, check HMRC's calculation and submit.

Your privacy

• We never ask for your HMRC or Government Gateway login. If any site or email asks you to type it somewhere other than gov.uk, don't.
• Everything is worked out in your browser. Your answers aren't sent anywhere.
• So you can come back later, your answers are saved in this browser on this device only. Use "Clear my answers" on the calculator to remove them. On a shared computer, clear them when you've finished.
• No accounts, no cookies, no tracking.

What the calculator covers

Employment (up to 3 jobs) with common job expenses, UK property income including joint lets, one self-employed business on the short pages (turnover under £90,000), Marriage Allowance, the High Income Child Benefit Charge, Class 2 and Class 4 National Insurance, CIS deductions, payments on account and collection through your tax code. It also covers UK savings interest and dividends, and relief-at-source pension payments and Gift Aid. Scottish rates are included.

Not covered yet: State or private pensions you receive, retirement annuity contracts, Gift Aid carried back to an earlier year, the pension annual allowance charge, student and postgraduate loans, capital gains, foreign income, Rent a Room relief, furnished holiday lets in earlier years, partnerships, more than one business, and loss relief against other income. If any of these apply, your real bill will differ.

Where the figures come from

All 2025-26 rates, allowances and box numbers were checked against GOV.UK and HMRC's 2025-26 forms in October 2026:

• Income Tax rates and allowances: Personal Allowance £12,570, reduced above £100,000; bands 20% up to £37,700, 40% to £125,140, 45% above.
• Scottish Income Tax 2025-26: 19% / 20% / 21% / 42% / 45% / 48%.
• National Insurance rates: Class 4 6% from £12,570 to £50,270 and 2% above; Class 2 £3.50 a week, small profits threshold £6,845.
• Same page: dividend allowance £500; dividend rates 8.75% / 33.75% / 39.35%; 0% starting rate for savings up to £5,000. Personal Savings Allowance: £1,000 / £500 / £0.
• Relief-at-source pensions and Gift Aid raise the basic and higher rate limits by the gross amount (and every Scottish limit above the starter rate), per HMRC's Pensions Tax Manual. Savings and dividends use UK bands for Scottish taxpayers.
• Property and trading allowances: £1,000 each.
• Marriage Allowance: £1,260 transfer, saving up to £252.
• High Income Child Benefit Charge: 1% per £200 over £60,000.
• Mileage rates, flat-rate expenses and working from home.
• Paying through your tax code, payments on account and penalties.
• Box numbers from HMRC's SA100 tax return (TR3 interest and dividends, TR4 reliefs), SA102 Employment, SA105 UK property and SA103S Self-employment (short) pages for 2026 (tax year 2025-26).

Found a mistake?

Tax rules have a lot of detail. If something looks wrong, trust GOV.UK and HMRC's own calculation over this site.