Self Assessment Tax Estimator 2026/27
Updated for the 2026/27tax year · Last updated
Enter your gross self-employment income and allowable business expenses to estimate your Self Assessment tax bill — income tax and Class 4 NI on taxable profit. The calculator also shows whether HMRC will require payments on account.
Estimated tax bill
£4,532
on £30,000 taxable profit
| Item | Amount |
|---|---|
| Gross income | £35,000 |
| Less: expenses | − £5,000 |
| Taxable profit | £30,000 |
| Income tax | £3,486 |
| Class 4 NI | £1,046 |
| Total tax & NI | £4,532 |
Payments on account: HMRC may require advance payments of £2,266 in January and £2,266in July towards next year’s bill (based on this year’s liability).
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How this calculator works
Taxable profit = gross income − allowable expenses. Income tax is calculated on taxable profit using the 2026/27 bands. Class 4 NI is also calculated on taxable profit (6% between £12,570–£50,270, then 2% above).
Payments on account are required when your combined income tax and Class 4 NI bill exceeds £1,000 and less than 80% was collected at source. Each instalment is 50% of the current year’s bill.
Frequently asked questions
You must file if you were self-employed as a sole trader (earning more than £1,000), a partner in a partnership, earned more than £100,000 in employment income, had rental income, had untaxed income over £2,500, or are a company director.
Paper returns: 31 October following the tax year end. Online returns: 31 January. Payment of tax: 31 January (balancing payment + first payment on account) and 31 July (second payment on account).
If your tax bill is over £1,000 and less than 80% was deducted at source, HMRC requires advance payments towards the following year's bill. Each payment is 50% of the current year's liability — paid in January and July. You can apply to reduce them if you expect your income to fall.
Yes. If you expect your tax liability to be lower next year, you can apply to reduce your payments on account using form SA303 or via your HMRC online account. Be careful — if you under-pay, HMRC charges interest on the shortfall.