1.Value of your cash allowance after tax:

Subtract your rate of income tax from your employers monthly cash allowance.

If you pay 22% tax you may also need to subtract NI contributions (NI is paid at between 8 -10% aprox).

If you pay 40% tax you will not need to deduct NI since your earnings will have put you past the threshold.

eg. a 40 % tax payer being given £500 per month would net £300 after tax.