I currently use this PD/NeT = %overdue

Example

PD= 43,257

Net= 146,200

from the above I know that the amount overdue is 29.6%

Question.

I need a formula that would tell me how much the customer has to pay in order to be at a set %, example 17%. Keep in mind that anything paid will reduce the NT and the PD by the same amout.

Example customer paid 7,000 then NT will now be NT-$7000 and PD-$7000.

so A $7,000 payment will make them be at 26%