UK Self Assessment Tax Calculator 2024-25
Calculate your Self Assessment tax bill for 2024/25: income tax on self-employed profits, Class 2 and Class 4 NI, plus payments on account estimates.
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How to use this calculator
- 1
Enter your total self-employed income before expenses for the tax year.
- 2
Deduct allowable business expenses — costs wholly and exclusively for business purposes (equipment, travel, subscriptions, professional fees, home office proportion, etc.).
- 3
Enter any personal pension contributions to reduce your adjusted net income and income tax.
- 4
The calculator shows income tax plus Class 2 and Class 4 NI — the three main components of a self-employed tax bill.
- 5
Payments on account are advance payments towards next year's tax bill: each is 50% of the current year's income tax + Class 4 NI, due 31 January and 31 July.
Frequently asked questions
What method does this tool use?
Profit is income minus expenses (never below zero). The pension contribution is deducted from profit, the personal allowance is reduced for incomes above £100,000, and the remainder is taxed at 20%, 40% and 45% on the standard bands. Class 2 and Class 4 National Insurance are calculated on profit and added to give a total bill. Take-home is profit minus the bill minus the pension contribution.
Which tax year and figures are built in?
The tool carries a 2024/25 label: a £12,570 allowance, 20% on the first £37,700 of taxable profit, 40% up to £125,140 and 45% above, Class 2 at £3.45 a week and Class 4 at 6% on profit between £12,570 and £50,270 and 2% above. These are the figures built into this tool. UK rates and thresholds change at least every tax year on 6 April, the tables are not updated automatically, and HMRC or a qualified adviser governs what applies to you.
How are payments on account calculated here?
The tool takes income tax plus Class 4 (Class 2 is excluded) and halves it, treating this year’s bill as a stand-in for next year. If that sum is under £1,000 it shows no payments instead. Real payments are set from your previous year’s return, so the tool’s figure is only a guide. The dates shown are 31 January and 31 July.
How is Class 2 treated?
As a flat £179.40 (£3.45 for 52 weeks) added whenever profit is above £12,570. Whether Class 2 is payable, credited or voluntary at your profit level depends on rules that have changed over time, so verify with HMRC. The line can be checked by comparing the total with and without it.
How are pension contributions handled?
The amount you enter is deducted from profit before income tax and before the personal allowance taper, and deducted again from take-home as cash paid out. Class 4 is still based on full profit. The tool does not model relief at source, carry-forward or annual limits.
Does it cover Scotland?
No. Only England, Wales and Northern Ireland bands are used. The tool has no region choice, so Scottish rates are not applied. Dividends, savings, rental income and employment income are also not included; enter only self-employed income and expenses.
Does it apply the trading allowance or capital allowances?
No. Expenses are whatever you type. A £1,000 trading allowance, capital allowances, cash-basis rules, loss relief and basis-period adjustments are not modelled, and a loss (expenses above income) is treated as zero profit.
How is the effective rate defined?
It is income tax plus Class 2 plus Class 4, divided by profit. It does not include the pension contribution and is shown as zero when profit is zero.
UK Self Assessment estimate: from profit to tax, Class 4 and payments on account
From income to taxable profit
The tool first subtracts expenses from self-employed income, flooring the result at zero. A pension contribution is then taken off, and the £12,570 personal allowance is reduced by £1 for each £2 of that figure above £100,000. The remainder is taxed at 20% on the first £37,700, 40% up to £125,140 and 45% above, using the figures labelled 2024/25 that are built into this tool. Only the England, Wales and Northern Ireland bands are applied, and no trading allowance or capital allowances are modelled.
National Insurance and payments on account
Class 4 is calculated on profit before pension: 6% between £12,570 and £50,270 and 2% above. Class 2 is added as a flat £179.40 when profit is over £12,570 — check HMRC for how Class 2 applies to you. Payments on account are half of income tax plus Class 4, shown only if that sum is at least £1,000, and the tool labels them as due on 31 January and 31 July. Because it uses this year’s bill as the base, they are an approximation of next year’s requests.
Worked example: £50,000 income, £10,000 expenses
Profit is £40,000 and taxable profit after the allowance is £27,430. Income tax is £5,486, Class 4 is £1,646 and Class 2 is £179.40, so the total bill is £7,311 and take-home is £32,689, an effective rate of 18.3%. Each payment on account shows as £3,566. A smaller case with £30,000 of income and £5,000 of expenses gives £25,000 of profit, £2,486 of tax, £746 of Class 4, a £3,411 bill and £1,616 per payment.
Worked example: £110,000 of profit with and without a pension contribution
With no pension, the allowance falls to £7,570, taxable profit is £102,430, income tax is £33,432 and the total bill is £37,068. Entering a £10,000 contribution leaves £100,000 of adjusted profit, restores the full allowance, lowers income tax to £27,432 and the total to £31,068, while Class 4 stays at £3,457. Take-home is £72,932 without the contribution and £68,932 with it, because the £10,000 is deducted as cash paid into the scheme.
| Profit | Pension | Income tax | Class 4 | Total bill | Each payment on account |
|---|---|---|---|---|---|
| £25,000 | £0 | £2,486 | £746 | £3,411 | £1,616 |
| £40,000 | £0 | £5,486 | £1,646 | £7,311 | £3,566 |
| £70,000 | £0 | £15,432 | £2,657 | £18,268 | £9,044 |
| £110,000 | £0 | £33,432 | £3,457 | £37,068 | £18,444 |
| £110,000 | £10,000 | £27,432 | £3,457 | £31,068 | £15,444 |
Limits of the estimate
The tool covers a single trade with no other income, loss relief or tax already deducted at source. Rates and thresholds change at least every tax year on 6 April, the tool’s tables are not updated automatically, and HMRC governs the figures that apply to your return.
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Results are estimates for informational purposes only and do not constitute professional financial, medical, legal, or technical advice. Read full disclaimer →