Net pay: enter the full gross amount deducted from your salary before tax is worked out.
Tax relief is given automatically through payroll.
Relief at source: enter the amount you actually pay from take-home pay
(before the 20% basic rate top-up is added by your provider).
Salary sacrifice: enter the amount of salary you have given up.
Your employer contributes this directly into your pension, reducing both your income tax and National Insurance.