Brett I usually will use an online calculator but I assume 10% for interest on these calculators because of the failure to pay penalty, which you also have. I then add something on for buffer, so if the $700 in the calculator ends up at $770 I will tell clients it will be “around $800 give or take” because of the interest and the 1/2% per month for failure to pay penalty, which keeps running until the 50 months of penalty run.
