Self Assessment Tax Return Calculator (UK, 2026/27)

Quick Answer: HMRC offers two calculators: the free estimator on GOV.UK, and the exact figure the online return works out once you submit. To estimate your own bill for 2026 to 2027, build a short sheet: taxable profit, minus the £12,570 personal allowance, taxed at 20%, 40% and 45%, plus Class 4 National Insurance at 6% on profits between £12,570 and £50,270 and 2% above that. Then add payments on account if last year's bill was £1,000 or more.

A Self Assessment tax return calculator turns your year's income and allowable expenses into an Income Tax and National Insurance estimate before HMRC sends the real figure. For sole traders and landlords in England, Wales and Northern Ireland, that is a few rows in Excel or Google Sheets. The rates below are the 2026 to 2027 figures published on GOV.UK.

What do HMRC's own calculators give you?

Start with what is free and official.

• The GOV.UK estimator. HMRC's Self Assessment tax calculator asks for weekly or monthly income and estimates Income Tax and Class 4 National Insurance. On 27 October 2026 the page still describes it as covering the 2025 to 2026 tax year, so it suits the return you are about to file rather than planning for the year now running.
• The calculation inside the online return. When you complete the return in your HMRC online account, the service works out the tax due from what you entered. That figure is the one you pay, but you only see it after entering every number.
• Commercial software. Bookkeeping apps show a running estimate as you categorise transactions. Our accounting software comparison covers the trade-offs.

A spreadsheet earns its place between those: it is yours, it shows every step, and you can rerun it each month with real figures.

Which rates apply for 2026 to 2027?

GOV.UK's Income Tax rates page and its self-employed National Insurance rates page list these figures for 6 April 2026 to 5 April 2027:

Rates change each April, so check both pages again before you rely on an estimate. Scotland sets its own Income Tax bands for Scottish taxpayers; the National Insurance rows still apply, but the Income Tax rows above do not.

How do you build the calculator in Excel or Google Sheets?

Put labels in column A and values or formulas in column B. The same formulas work in both programs.

A few of those need explaining.

• B3 compares actual expenses with the £1,000 trading allowance, which you can use instead of claiming expenses. MIN keeps whichever leaves the lower profit. If you have rental income, the separate £1,000 property allowance works the same way on that income before it goes into B4.
• B6 applies the taper. The formula uses total income as a stand-in for adjusted net income; pension contributions and Gift Aid can lower the real figure.
• B8 to B10 use taxable income, so the 20% band is the first £37,700 (that is £50,270 minus £12,570) and the 45% rate starts once taxable income passes £125,140.
• B11 uses trading profit only, because Class 4 is charged on self-employed profits, not on rent or a salary.

If you also have a job, tax on the salary is usually collected through PAYE. Add the salary to B4 to place your profit in the right band, then subtract the tax already taken through payroll to see what is left for Self Assessment.

A worked example

Priya is a self-employed bookkeeper in Leeds. In 2026 to 2027 she invoices £48,000 and has £9,500 of allowable expenses: software, a share of phone costs, training and mileage. She has no other income.

• Profit: £48,000 − £9,500 = £38,500 (better than the trading allowance, which would leave £47,000).
• Taxable income: £38,500 − £12,570 = £25,930, all inside the basic-rate band.
• Income Tax: £25,930 × 20% = £5,186.00.
• Class 4 NI: (£38,500 − £12,570) × 6% = £1,555.80.
• Class 2: profits are above £7,105, so it is treated as paid: £0.
• Estimated 2026 to 2027 bill: £6,741.80.

How do payments on account change what you pay?

HMRC's payments on account guidance explains that most people pay towards next year's bill in two instalments, due by midnight on 31 January and 31 July, and each is half of the previous year's bill. Class 4 is included. You do not make them if last year's bill was under £1,000, or if more than 80% of last year's tax was collected outside Self Assessment, for example through PAYE.

Add three rows to the sheet:

• B13, last year's bill: typed in.
• B14, each payment on account already made for this year: =IF(B13<1000,0,B13/2).
• B15, balancing payment: =B12-2*B14.

Continuing with Priya, suppose her 2025 to 2026 bill was £5,200. She pays £2,600 on 31 January 2027 and £2,600 on 31 July 2027. Her 2026 to 2027 bill of £6,741.80 leaves a balancing payment of £1,541.80, due by 31 January 2028. That same day the first payment on account for 2027 to 2028 is due, half of £6,741.80 or £3,370.90, so the January 2028 total is £4,912.70.

In a first year of self-employment the jump is sharper. With no earlier bill, nothing is paid during the year, and in January the whole bill and the first payment on account for the next year arrive together. On Priya's numbers, that would be £6,741.80 + £3,370.90 = £10,112.70.

Where do the income and expense figures come from?

The arithmetic is the easy part; B1 and B2 are where estimates go wrong. Most sole traders can rebuild both from their business current account and any card used for business costs.

1. Download a statement for each month of the tax year. UK statements usually run monthly, and the tax year starts on 6 April, so you will need some March and April lines from the edge statements. Our explainer on what a current account statement shows covers the layout, and there are bank-specific notes for Barclays and HSBC.
2. Put every line in one sheet, then add a column that marks each row as income, an allowable expense, personal, or a transfer between your own accounts. Transfers and personal spending stay out of B1 and B2.
3. Total each category with SUMIFS, for example =SUMIFS(Lines!D:D,Lines!E:E,"Expense",Lines!A:A,">="&DATE(2026,4,6),Lines!A:A,"<="&DATE(2027,4,5)), and link the totals into B1 and B2.

If a bank only gives you PDFs, QuickBankConvert can turn each statement into CSV or Excel rows (date, description, amount, balance) so step 2 starts from a spreadsheet instead of retyping. The bank's own CSV export is just as good where it covers the dates you need. Either way, keep the statements: our guide to how long to keep bank statements explains why the records matter after you file. GOV.UK's list of allowable expenses if you're self-employed is the reference for what can go in column B2.

Deadlines and Making Tax Digital

For the 2025 to 2026 tax year, GOV.UK's deadlines page gives 31 October 2026 for paper returns and 31 January 2027 for online returns and payment. Separately, HMRC's Making Tax Digital for Income Tax guidance says people with qualifying income over £50,000 in 2024 to 2025 should have started using it from 6 April 2026, with lower thresholds of £30,000 from April 2027 and £20,000 from April 2028. If that applies to you, compatible software will hold your records, and the sheet above becomes a cross-check rather than your main record.

This sheet is an estimate for planning. It does not cover student loan repayments, the High Income Child Benefit Charge, capital gains, losses, or Scottish rates; your submitted return and HMRC's calculation are what count.