How we calculate

Where the figures come from

Every rate, band and threshold lives in a small set of rate tables in the code, one for each tax, and is checked against official sources: HMRC's rates and allowances and employer rates and thresholds, the Scottish Government's income tax bands, the Student Loans Company, DWP's benefit and pension rates, The Pensions Regulator's auto-enrolment thresholds, and the Budget's overview of tax legislation and rates. You can see every figure on the tax rates page, and every source is linked below.

How take-home pay is worked out

• Income tax follows HMRC's ordering: earnings and other non-savings income first, then savings, then dividends. Your Personal Allowance is used against earnings first and falls by £1 for every £2 of adjusted net income over £100,000.
• Scotland has its own bands for earnings, pensions and rental income. Savings and dividends are taxed at UK rates wherever you live.
• National Insurance and student loans are worked out per payday, exactly as payroll does. A bonus month is charged on its own, which is why a big bonus can cost less NI than you expect.
• Tax codes are read the way PAYE reads them: S and C prefixes, L, M, N and T suffixes, K codes with the rule that tax can never exceed half your pay, BR, D0 to D3, 0T, NT and emergency W1, M1 and X codes.
• Pensions: salary sacrifice reduces pay for tax, NI and student loan. Net pay schemes reduce pay for tax only. Relief at source contributions are taken after tax, the provider adds 20%, and higher rate relief comes through your tax return.
• Company cars use the CO2 and electric range bands, with optional remuneration rules above 75g/km.
• Self Assessment covers income your payslip does not: freelance profit with Class 4 NI, rent, dividends, savings, the Child Benefit charge and relief you can claim back.

Retirement projections

The planner works in today's money. Contributions come from your take-home calculation, growth is after fees and inflation, and tax in retirement uses the same engine, including the threshold freeze to April 2031. A Monte Carlo simulation runs 1,000 different market paths to show how likely your money is to last.

How we test the numbers

The calculation engine is covered by an automated test suite of worked examples that runs before every release. It checks income tax in the rest of the UK and Scotland, the allowance taper above £100,000, tax codes including the K code limit and emergency codes, payroll's cumulative PAYE rounding, National Insurance per payday, student loan rounding, pension relief methods, company car rates, the Child Benefit charge, self-employment, Marriage Allowance and State Pension age. A release that changes any of those answers does not go out until the change is understood.

The AI assistant

The assistant reads the figures you have entered and answers using the same calculation engine. It cannot invent numbers about your pay: any what-if runs through the calculator first. It gives guidance, not regulated financial advice.

Keeping it current

We update the figures each April, after every Budget and Spring Statement, and whenever HMRC or the Scottish Government publishes a change. The date the rates were last checked is shown in the footer of every page, and each change is recorded in the update log below.

Corrections

When we find an error, or someone reports one, we confirm it against the official source, fix it, add a test so it cannot come back, and record it in the update log with the date.

Independence

Best UK Tax Calculator is built and run by Voidmode Studios. No company pays to change a calculation or its result. If we ever earn a commission from a product we mention, the page will say so clearly next to it.

Limits

These are estimates to help you plan. Your actual pay can differ because of cumulative PAYE adjustments, mid-year changes to your tax code, benefits HMRC has estimated, or details of your pension scheme. If something looks wrong on your payslip, check your tax code in the HMRC app. For decisions about pensions and investments, consider regulated financial advice.

Official sources

Income tax and National Insurance

• Income Tax rates and Personal Allowances (GOV.UK)
• Income Tax rates and allowances for current and past years (HMRC)
• Scottish Income Tax (GOV.UK)
• Welsh Income Tax (GOV.UK)
• National Insurance rates and categories (GOV.UK)
• Rates and allowances: National Insurance contributions (HMRC)
• National Insurance: how much you pay (GOV.UK)
• National Insurance classes (GOV.UK)
• National Insurance category letters (GOV.UK)
• National Insurance and tax after State Pension age (GOV.UK)
• CA44: National Insurance for company directors (HMRC)
• Rates and thresholds for employers 2026 to 2027 (HMRC)
• Employment Allowance (GOV.UK)
• Self-employed National Insurance rates (GOV.UK)
• Tax codes (GOV.UK)
• Tax codes: what your tax code means (GOV.UK)
• Emergency tax codes (GOV.UK)
• PAYE Manual (HMRC)
• Check your Income Tax for the current year (HMRC)

Pay, benefits and allowances

• Repaying your student loan: what you pay (GOV.UK)
• National Minimum Wage and National Living Wage rates (GOV.UK)
• Salary sacrifice and the effects on PAYE (HMRC)
• Tax on company benefits: company cars (GOV.UK)
• Calculate tax on company cars (HMRC)
• Expenses and benefits: company cars and fuel (GOV.UK)
• Child Benefit: what you'll get (GOV.UK)
• High Income Child Benefit Charge (GOV.UK)
• Marriage Allowance (GOV.UK)
• Blind Person's Allowance (GOV.UK)

Savings, dividends, property and self-employment

• Tax on dividends (GOV.UK)
• Tax on savings interest (GOV.UK)
• Tax-free allowances on property and trading income (HMRC)
• Renting out a property: paying tax (GOV.UK)
• Changes to tax relief for residential landlords (HMRC)
• Understand your Self Assessment tax bill: payments on account (GOV.UK)

Pensions and retirement

• Tax on your private pension: tax relief (GOV.UK)
• Tax on your private pension: annual allowance (GOV.UK)
• Tax on your private pension: lump sum allowance (GOV.UK)
• Tax on your private pension contributions (GOV.UK)
• Workplace pensions: what you, your employer and the government pay (GOV.UK)
• The new State Pension: what you'll get (GOV.UK)
• Check your State Pension age (GOV.UK)
• Check your State Pension forecast (GOV.UK)
• Plan your retirement income (GOV.UK)
• Retirement Living Standards (Pensions UK)
• Tax when you get a pension (GOV.UK)
• Check how to claim a tax refund on your pension (GOV.UK)
• Claim a tax refund on your pension by post (P55, P53Z, P50Z) (HMRC)

Capital Gains Tax

• Capital Gains Tax rates (GOV.UK)
• Capital Gains Tax rates and annual tax-free allowances (HMRC)
• Capital Gains Tax allowances (GOV.UK)
• Capital Gains Tax: if you make a loss (GOV.UK)
• Capital Gains Tax: gifts to your spouse or charity (GOV.UK)
• Tax when you sell property: work out your gain (GOV.UK)
• Report and pay your Capital Gains Tax: if you sold a property in the UK (GOV.UK)
• Business Asset Disposal Relief (GOV.UK)
• Tax when you sell your home (GOV.UK)

Buying property: stamp duty, LBTT and LTT

• Stamp Duty Land Tax: residential property rates (GOV.UK)
• Higher rates of Stamp Duty Land Tax (HMRC)
• Rates of Stamp Duty Land Tax for non-UK residents (HMRC)
• Land and Buildings Transaction Tax: residential property (Revenue Scotland)
• The Additional Dwelling Supplement (ADS) (Revenue Scotland)
• Scottish Budget 2026 to 2027: tax policy (Scottish Government)
• Land Transaction Tax rates and bands (Welsh Revenue Authority)
• Land Transaction Tax and Anti-avoidance of Devolved Taxes (Wales) Act 2017, Schedule 5 (higher rates) (legislation.gov.uk)
• Written statement: Draft Budget 2026-27, Welsh taxes (Welsh Government)

Update log

• 14 October 2026: Linked every calculator to the official pages its figures are checked against. Added hourly pay pages, what pension pots pay in retirement, and the Retirement Living Standards from Pensions UK.
• 6 October 2026: Checked every 2026/27 rate and threshold against HMRC, the Scottish Government, the Student Loans Company, DWP and The Pensions Regulator.