Self Assessment Tax Calculator

For 2025-26, the personal allowance is £12,570. The basic rate is 20% on income from £12,571 to £50,270. The higher rate is 40% on income from £50,271 to £125,140. The additional rate is 45% on income above £125,140. The personal allowance tapers by £1 for every £2 earned above £100,000.

Mandatory Class 2 NI was abolished from 6 April 2024. Self-employed people with profits at or above the Small Profits Threshold (£6,845 for 2025-26; £6,725 for 2024-25) are automatically treated as having paid Class 2 for pension/benefit entitlement (£0 charge) — this includes everyone in the band between the Small Profits Threshold and the £12,570 Lower Profits Limit, who get the National Insurance credit without paying. Those with profits below the Small Profits Threshold can pay Class 2 voluntarily (£3.50/week for 2025-26) to protect their State Pension record. Class 4 NI is 6% on profits between £12,570 and £50,270, plus 2% on profits above £50,270.

If your total income tax and Class 4 NI liability exceeds £1,000, HMRC requires two advance payments (payments on account) towards next year's bill. Each payment is half the previous year's tax and Class 4 NI. They are due on 31 January and 31 July. You can apply to reduce them if your income is expected to fall.

Yes, personal pension contributions receive tax relief. Basic rate relief (20%) is usually added automatically by your pension provider. If you are a higher rate taxpayer, you claim the extra 20% through your self assessment return. Pension contributions also extend your basic rate band, potentially reducing higher rate tax.

The trading allowance gives you £1,000 of tax-free trading income per year. If your gross trading income is £1,000 or less, you do not need to declare it. If your income is above £1,000, you can choose to deduct the £1,000 allowance instead of your actual expenses, whichever gives the better result.

Marriage Allowance lets a lower-earning spouse or civil partner (whose income is below the £12,570 personal allowance) transfer £1,260 of their unused allowance to you. As the recipient you do not get extra personal allowance — instead you receive a tax reducer of £252 (£1,260 × 20%) off your income tax bill. You can only claim it if you are a basic-rate taxpayer. Tick "Receive Marriage Allowance" only if your partner transfers their allowance to you.

Your £12,570 personal allowance is reduced by £1 for every £2 of adjusted net income above £100,000, disappearing entirely at £125,140. Adjusted net income is your income minus your gross pension contributions and grossed-up Gift Aid donations. Paying into a pension can therefore restore some or all of your personal allowance — bringing adjusted net income down to £100,000 keeps the full allowance, the so-called 60% tax trap mitigation.