Salary sacrifice
Salary sacrifice usually means you agree to reduce contractual gross pay, and your employer pays the sacrificed amount into your pension.
Because payroll gross pay is reduced, income tax and employee National Insurance are usually calculated on the lower amount. Employer rules can still affect the exact payslip result.
Net pay arrangement
In a net pay arrangement, pension contributions are usually deducted before income tax is calculated.
Employee National Insurance is usually still based on full pay, so the NI result can differ from salary sacrifice.
Relief at source
Relief at source contributions are usually deducted from after-tax pay. The pension provider then claims basic-rate tax relief and adds it to the pension.
Higher-rate or additional-rate taxpayers may need to claim extra relief separately. This calculator does not model separate tax relief claims.
What to check on your payslip
Look for pension labels, taxable pay, gross pay, NI-able pay and whether the pension deduction appears before or after tax.
If unsure, ask payroll or your pension provider which arrangement applies before relying on a calculator setting.