From gross to take-home
Your gross salary is never what you take home. First, income tax applies above your personal allowance (£12,570), at 20%, 40% and 45%. Then National Insurance takes 8% between the thresholds and 2% above. Many people also repay a student loan (9% above the Plan 2 threshold) and pay into a pension.
Pension contributions made by salary sacrifice come off before tax, so they lower your tax bill while building your retirement pot.
Scotland note
These figures use the England/Wales/NI bands. Scotland sets its own income tax rates, so a Scottish taxpayer's take-home differs slightly.
Common questions
Income tax, National Insurance, and optionally a Plan 2 student loan and pension contributions. The result is what actually lands in your account.
It uses the rates for England, Wales and Northern Ireland. Scotland has its own income tax bands, so a Scottish taxpayer would see slightly different figures.
Pension contributions (via salary sacrifice) come off before tax, so they reduce both your taxable pay and your take-home — but build your pot.