What distinguishes a true salary sacrifice from a standard post-tax deduction, like a loan repayment?

Answer

A true salary sacrifice is an adjustment 'above the line' directly impacting the taxable pay figure.

Salary sacrifice is a pre-tax reduction, altering the base gross salary before Income Tax and NI calculations, unlike post-tax deductions which are taken off after those calculations are complete.

What distinguishes a true salary sacrifice from a standard post-tax deduction, like a loan repayment?
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