Bonus tax calculator

How this calculator works

• We calculate your deductions on your salary alone.
• We calculate them again with the bonus included.
• The difference is the tax, National Insurance and student loan attributable to the bonus.

Assumptions

• The bonus is paid in the same tax year as the salary you enter.
• Your pension percentage is applied to the bonus as well as your salary.
• You are aged under State Pension age and pay Class 1 employee National Insurance where relevant.
• You have the standard tax code with no adjustments, restrictions or underpayments carried forward.
• Income is spread evenly across the tax year, so no month-by-month PAYE smoothing effects are modelled.
• No other taxable income, taxable benefits in kind, salary sacrifice arrangements or Marriage Allowance transfers are included unless entered.
• Pension contributions are treated as a net pay (salary sacrifice equivalent) deduction taken before income tax is applied.

Limitations

• A bonus paid in one month can be over-deducted in that period and corrected by later payslips.
• A large bonus can push income past £100,000 and taper the personal allowance — the calculator shows this, but check the assumptions.
• Bonus sacrifice into a pension is not modelled separately.

Sources for 2025/26

• HMRC — Income Tax rates and Personal Allowances
• HMRC — National Insurance rates and categories
• Scottish Government — Scottish Income Tax
• GOV.UK — Repaying your student loan