1. figure out the insurance, pmi and escrow then take that out of the equation.
2. if they made extra payments it will be very hard to calculate because you will have to go through every payment and calculate how much was paid to principle and how much was paid to interest.
3. there are spreadsheets available online for free if you have excel, where you just type in the payment date and amount for every payment and it will calculate the remaining balance.
