untaxedadjective
uk/ˌʌnˈtækst/usTAXused to describe something on which tax has not been paid, or does not need to be paid:
The underground, untaxed economy is estimated to be worth as much as 40% of the official economy.
Because part of the income you put into your pension is untaxed, the Government is giving you 23p for each £1 invested.