UK Self-Assessment Tax Calculator (2026/27)
Estimate your Self-Assessment bill as a sole trader, freelancer, or partner. Enter your annual profits (turnover minus allowable expenses) and the calculator works out Income Tax via the standard bands plus National Insurance Class 2 (voluntary) and Class 4. It also tells you what each payment on account will be in January and July.
How is this calculated?
Income Tax is calculated on (profits − Personal Allowance) using the standard England/Wales/NI bands: 20% on the first £37,700 of taxable income, 40% up to £125,140, and 45% above. National Insurance Class 4 is paid through Self Assessment: 6% on profits between £12,570 and £50,270, then 2% above. Class 2 is voluntary post-2024 reform but adds £3.45/week (£179.40/year) for the contribution-record benefit once profits exceed £6,725. Payments on account are 50% of your total tax + NI bill, due 31 January (current year) and 31 July (following year).
Frequently Asked Questions
Who has to file a Self-Assessment return?
Anyone who is self-employed (sole trader or partner), earned more than £1,000 from side gigs, received untaxed income (rent, dividends above £500), is a higher-rate taxpayer claiming pension relief, has capital gains above the annual exempt amount, or HMRC has specifically asked them to. The threshold for sole-trader registration is £1,000 of trading income.
What are payments on account?
If your last Self-Assessment bill was over £1,000 (and less than 80% was collected at source), HMRC requires two advance payments toward next year's bill: 50% on 31 January and 50% on 31 July. They're a forecast — when you file the actual return, any difference is a balancing payment (or refund). First-year filers don't have payments on account to pay; second year is when they kick in.
What expenses can I deduct as a sole trader?
Wholly and exclusively business expenses: office costs, travel and subsistence, professional fees, marketing, equipment (with capital allowances for big-ticket items), use-of-home calculations, training relevant to your existing trade. Personal/private expenses, business entertaining, and capital expenditure (claimed via capital allowances instead) are not deductible. Keep records for at least 5 years after the 31 January following the tax year.
When do I have to register for Self-Assessment?
Register with HMRC by 5 October following the end of the tax year you started self-employment. The deadline to file online is 31 January after the end of the tax year (paper filers must submit by 31 October). Late filing is an automatic £100 penalty plus interest on unpaid tax.
Does this calculator include the High Income Child Benefit Charge?
No — HICBC is not modelled here. If your adjusted net income is between £60,000 and £80,000 (thresholds raised from April 2024), you pay back some or all of any Child Benefit you receive via Self Assessment. Factor this in separately if relevant.
Last updated: May 2026 · Rates sourced from HMRC