Self Assessment Tax Calculator (2026/27)

Estimate your bill with the self-assessment tax calculator

Put your figures into the tool above. Add your self-employment profit, any other untaxed income such as rent or dividends, and the tax already paid through PAYE if you also have a job. The calculator returns your estimated income tax, Class 4 NI and the payments on account HMRC may ask for next. Treat the result as a planning figure: your filed return, with every expense and relief, is the official number.

How is self assessment tax calculated?

Self assessment isn't a separate tax. It's the system HMRC uses to collect tax on income that wasn't taxed at source. Your bill is built from the same income tax rates that apply to everyone, plus Class 4 National Insurance if you're self-employed, minus any tax you've already paid through a job or pension.

The order of operations matters. HMRC stacks your income, applies your Personal Allowance first, then taxes each slice in its band:

Self-assessment tax = Income Tax on taxable income + Class 4 NI on profits − tax already paid at source

For the 2026/27 tax year, your Personal Allowance is £12,570. You pay no income tax on income up to that point. Above it, the first £37,700 of taxable income is taxed at the 20% basic rate, the slice from £37,700 to £125,140 at the 40% higher rate, and anything above £125,140 at the 45% additional rate.

If you're a sole trader or landlord, those bands apply to your profit - your turnover minus allowable business expenses - not your turnover. Getting your expenses right is what keeps the bill honest.

Class 4 National Insurance on your profits

On top of income tax, self-employed people pay Class 4 NI. For 2026/27 you pay 6% on profits between £12,570 and £50,270, and 2% on profits above £50,270. Class 2 NI is no longer payable if your profits are above the Small Profits Threshold of £7,105 - you still get the National Insurance credit towards your State Pension without paying it. Below that threshold, Class 2 is voluntary at £3.65 a week if you want to protect your record.

Employees pay Class 1 NI instead, which the National Insurance calculator handles separately. If your only income is a salary, you usually don't file a return at all.

If you also have a PAYE job

Many people who file have a day job plus a side income. The tax deducted from your salary through PAYE counts towards your total bill. Your return adds up tax due on everything, then subtracts what you've already paid, so you only settle the gap. The same works in reverse - if too much was taken, you're due a refund, which the tax refund calculator can help you estimate.

Worked example: a freelance designer on £45,000 profit

Priya is a self-employed graphic designer in Manchester. After deducting her allowable expenses - software, a share of her home office, professional insurance - her profit for 2026/27 is £45,000. She has no other income. Here's how her self-assessment bill is calculated.

Step 1 - Income tax. Her Personal Allowance of £12,570 comes off first, leaving £32,430 of taxable income. That all sits within the basic-rate band, so it's taxed at 20%:

• £32,430 × 20% = £6,486 income tax

Step 2 - Class 4 NI. She pays 6% on the profit between £12,570 and £45,000:

• (£45,000 − £12,570) = £32,430
• £32,430 × 6% = £1,945.80 Class 4 NI

Step 3 - Total bill. £6,486 + £1,945.80 = £8,431.80 for the year. Because she had no tax deducted at source, she pays the whole amount through self assessment.

A second example: a higher-rate landlord

Now take Marcus, who has a £50,000 salary taxed through PAYE plus £18,000 of rental profit. His salary uses up his Personal Allowance and most of his basic-rate band. By the time his rental profit is stacked on top, much of it falls in the 40% higher-rate band. He's already paid tax on his salary through PAYE, so his self-assessment bill is essentially the tax on the rental profit - a large chunk at 40%. Rental income doesn't attract Class 4 NI, which is the key difference from trading profit. If your let property is mortgaged, the Section 24 landlord tax calculator shows how finance-cost relief affects the result.

2026/27 rates and thresholds

These are the figures the self-assessment tax calculator uses for England, Wales and Northern Ireland. Scotland sets its own income tax bands - see the note below the table.

Figures checked for the 2026/27 tax year against HMRC. You can confirm them and read the official filing guidance at gov.uk's self-assessment pages and the income tax rates page.

If you're a Scottish taxpayer

Scotland has its own income tax rates and bands, with more steps than the rest of the UK and a top rate above the rUK additional rate. The £12,570 Personal Allowance and the Class 4 NI rates are still UK-wide, but the income tax slices differ. If your main home is in Scotland, use the Scotland tax calculator for the correct bands before you file.

Payments on account: the bit that surprises people

Seeing your first self-assessment bill almost double can be a shock, and payments on account are usually the reason. If you owe tax through self assessment, HMRC often asks you to pay towards next year's bill in advance, on the assumption your income will be similar.

Each payment on account is half of your previous year's tax bill. They're due on 31 January and 31 July. So in your first January you can end up paying last year's tax in full plus the first instalment towards the year ahead - effectively 150% of the bill in one go. After that, the rhythm settles: two instalments a year, with a balancing payment each January for anything still outstanding.

There are exceptions - small bills and income mostly taxed at source can mean no payments on account are due. The thresholds for that are set by HMRC and explained on the gov.uk page linked above. If your income has dropped, you can apply to reduce your payments on account, but underestimating means interest, so be realistic.

How much should I set aside for self assessment?

The honest answer depends on your profit, but a practical habit beats a precise guess. For a basic-rate sole trader, setting aside around a quarter to a third of your profit usually covers income tax and Class 4 NI with room to spare. Higher earners should set aside more, because the 40% band and payments on account both push the figure up.

• Open a separate tax savings pot and move money across every time you get paid, not at the year end.
• Budget for January and July if you make payments on account, so the second instalment doesn't sting.
• Claim every allowable expense - mileage, home-office costs, equipment, subscriptions. Each pound of genuine expense reduces both your income tax and your Class 4 NI.
• Consider pension contributions, which can reduce the income that's taxed at the higher rate.

Deadlines and penalties to watch

The self-assessment year runs to 5 April. For the 2025/26 return you file in the following year, the key dates are 31 October for a paper return and 31 January for filing online and paying what you owe. Miss the online deadline and HMRC issues an automatic £100 penalty even if you owe nothing, with further penalties and interest the longer it slips. The tax deadline tracker keeps these dates in view.

Common mistakes people make

• Forgetting payments on account. Budgeting only for the tax owed, then being blindsided by the extra instalment in January.
• Filing turnover instead of profit. You're taxed on profit after allowable expenses, not on everything that landed in your account.
• Missing other income. Savings interest above your allowance, dividends, and rental profit all belong on the return - HMRC receives this data and cross-checks it.
• Applying England's rules in Scotland. Scottish taxpayers have different income tax bands; using rUK rates gives the wrong figure.
• Leaving it to the last week. A forgotten Government Gateway password in late January is a classic, and the £100 penalty applies whether or not you owe tax.
• Confusing the trading view with the filing view. If you want a running picture of your ongoing sole-trader position rather than a return estimate, the self-employed tax calculator is built for that.

For the underlying income tax maths on a single income figure, the income tax calculator breaks down each band.

This self-assessment tax calculator and the figures above are estimates for guidance only and not personal tax or financial advice. Check your own position with HMRC or a qualified adviser before you file.

Related tax calculators

Carry on planning with these tools: the self-employed tax calculator for an ongoing trading view, the National Insurance calculator for your Class 4 or Class 1 contributions, and the tax refund calculator if you think you've overpaid.

You might also need

• Tax Rebate Checker, check the reliefs to put on your return.

Related tools

• Do I need to file a tax return?, check whether you must file at all.