🇬🇧 Self Assessment Tax Calculator
Gross personal pension contributions (relief at source).Tax Breakdown
If you’re self-employed, the hard part isn’t filling in the tax return, it’s knowing how much to keep back for it. This calculator estimates your Self Assessment bill from your profit: Income Tax, Class 4 National Insurance, student loan repayments and the payments on account HMRC will ask for. It works for 2025/26 (the return due by 31 January 2027) and 2026/27, and for both Scottish and non-Scottish taxpayers.
Enter profit, not turnover. Profit is what’s left after allowable expenses, so £70,000 of sales with £20,000 of expenses means you enter £50,000. Pension contributions should be the gross amount you paid into a personal pension, including the 20% basic-rate relief your provider claims.
An example: £50,000 profit with a Plan 2 student loan
| Amount | |
|---|---|
| Profit | £50,000.00 |
| Personal Allowance | £12,570.00 |
| Taxable income | £37,430.00 |
| Income Tax (20%) | £7,486.00 |
| Class 4 NI (6%) | £2,245.80 |
| Plan 2 student loan (2026/27 threshold) | £1,855.35 |
| Left after tax | £38,412.85 |
Without the student loan, the bill is £9,731.80, and each payment on account would be £4,865.90 (half of the Income Tax plus Class 4 NI).
Key dates for the 2025/26 tax return
The 2025/26 tax year ran from 6 April 2025 to 5 April 2026. These dates are from GOV.UK:
| What | Deadline |
|---|---|
| Register for Self Assessment (first time) | 5 October 2026 |
| Paper tax return | 31 October 2026 |
| Online tax return | 31 January 2027 |
| Pay 2025/26 tax, plus first payment on account for 2026/27 | 31 January 2027 |
| Second payment on account for 2026/27 | 31 July 2027 |
Miss the online deadline and there’s an automatic £100 penalty, even if you don’t owe anything. After three months it’s £10 a day for up to 90 days (£900), then another 5% of the tax due or £300, whichever is higher, at six months and again at twelve. Paying late adds separate 5% penalties at 30 days, six months and twelve months, plus interest.
Payments on account, and the first-year shock
Payments on account are advance payments towards next year’s bill. Each one is half of the previous year’s Income Tax and Class 4 NI, due on 31 January and 31 July. You don’t have to make them if your last bill was under £1,000, or if more than 80% of your tax was already collected through PAYE.
They catch a lot of people out in their first year. Take a sole trader in England with £30,000 profit for 2025/26. Their bill is £4,531.80 (£3,486 Income Tax and £1,045.80 Class 4 NI), so each payment on account is £2,265.90. On 31 January 2027 they pay the full 2025/26 bill and the first payment on account together: £6,797.70. Another £2,265.90 follows on 31 July. Any difference is settled with a balancing payment the following January.
How much to set aside
The simplest habit is to move a fixed percentage of every payment you receive into a separate savings account. Based on 2026/27 rates for someone in England with no pension or student loan:
| Annual profit | Income Tax | Class 4 NI | Total | Roughly |
|---|---|---|---|---|
| £20,000 | £1,486.00 | £445.80 | £1,931.80 | 10% |
| £30,000 | £3,486.00 | £1,045.80 | £4,531.80 | 15% |
| £50,000 | £7,486.00 | £2,245.80 | £9,731.80 | 20% |
| £70,000 | £15,432.00 | £2,656.60 | £18,088.60 | 26% |
With a student loan, add 9% of profit above your plan’s threshold (6% for a Postgraduate Loan). In your first year, put aside extra for that first payment on account. And if you have a salary as well, your PAYE pay is taxed first, which can push more of your self-employed profit into the higher bands; the Take Home Pay Calculator helps with the employed side.
Class 4 National Insurance 2026/27
| Annual profit | Rate |
|---|---|
| Up to £12,570 | 0% |
| £12,570 to £50,270 | 6% |
| Over £50,270 | 2% |
Class 2 National Insurance has been voluntary since 6 April 2024, so the calculator doesn’t include it. If your profits are low, paying it voluntarily can still be a cheap way to protect your State Pension record.
Where the estimate can go wrong
The usual mistakes are entering turnover instead of profit, picking the wrong student loan plan, or forgetting other income. Rental income, savings interest and dividends all go on the same tax return and can change which band your profit falls into.
Landlords can use the calculator for a rough Income Tax figure, but rental profits don’t pay Class 4 National Insurance. If rent is your only income, ignore the NI line.
From April 2026, sole traders and landlords with qualifying income over £50,000 also have to keep digital records and send quarterly updates under Making Tax Digital for Income Tax. It doesn’t change how much tax you pay, but it does change how you report it.
Questions people ask
When is the Self Assessment deadline for 2025/26?
The online return and payment deadline is 31 January 2027. Paper returns were due by 31 October 2026.
How much tax will I pay on £30,000 of self-employed profit?
In England, Wales or Northern Ireland, about £4,531.80 for 2026/27: £3,486 Income Tax and £1,045.80 Class 4 National Insurance.
Do I have to make payments on account?
Yes, unless your last bill was under £1,000 or more than 80% of your tax was collected at source. Each payment is half of last year’s bill, due on 31 January and 31 July.
Can landlords use this calculator?
Yes, for an Income Tax estimate. Rental profits don’t pay Class 4 National Insurance, so if rent is your only income, the NI figure will be too high.
Is this calculator approved by HMRC?
No. It’s an independent tool for estimates; your tax return is what HMRC uses.
Related: UK Income Tax bands 2026/27 · UK VAT Calculator · Student Loan Repayment Calculator
Figures are estimates. They aren’t tax advice; check GOV.UK or an accountant before you file.