Self Assessment Tax Calculator UK 2026
Estimate your UK Self Assessment tax bill or refund for the 2026 tax year. Enter your total income and any PAYE tax already withheld to see if you owe HMRC money or are due a refund. Works for employees filing Self Assessment and for those with mixed income sources.
From your P60 or payslips
From your P60 or employer
Estimated Refund
+£14
HMRC withheld more tax than needed — you should receive a refund.
Frequently Asked Questions
Who needs to complete a Self Assessment tax return?
You must complete a Self Assessment return if you: are self-employed with income over £1,000; earned over £100,000; have untaxed income (rental, savings interest, dividends); are a company director; or received a P800 or notice to file from HMRC.
How is Self Assessment tax calculated?
Self Assessment tax = income tax on total income (minus personal allowance and reliefs) minus any PAYE tax already paid. If your employer withheld more tax than your actual liability, you get a refund. If less, you pay the balance by 31 January.
What is the Self Assessment deadline?
For the 2026 tax year (ending 5 April 2026): online returns are due 31 January 2027; paper returns are due 31 October 2026. Tax payments are due 31 January 2027 (with Payments on Account potentially due 31 July 2026 and 31 January 2027).
What expenses can the self-employed deduct?
Self-employed people can deduct allowable business expenses including: office costs, travel and vehicle costs, clothing (uniforms/protective gear), staff costs, stock, financial and legal costs, marketing, and training directly related to the business. Personal expenses are not allowable.
What are Payments on Account?
If your Self Assessment tax bill is over £1,000, HMRC requires advance payments called Payments on Account: 50% due 31 January and 50% due 31 July the following year, based on your previous year's tax bill. This can cause a large payment in the first year you file.