
Quoting
budwad
Any excess payments in a regular payment only reduces the principal at the back end of the loan. Meaning that the credit to interest will only be reduced (each month) based on the principal balance for that month. The principal balance does not change no matter how much they pay and the principal is reduced by the excess money over the monthly payment at the end of the loan. But each monthly payment is based on the front end of the schedule.
You can take a 30 year mortgage and pay it off in 15 years by paying your monthly payment (principal and interest) and adding the next month's principal amount to the payment. You don't get charged interest for that next payment because you already paid it. You skip the next line on the schedule.
I'm sure I confused you.