How extra payments work
Every dollar you pay above your scheduled principal & interest goes straight to the loan balance. Because future interest is charged on that lower balance, a small extra amount each month snowballs into a much shorter term and large interest savings — especially early in the loan, when most of your normal payment is interest.
Extra monthly vs biweekly vs lump sum
Three common strategies reach the same goal: a fixed extra each month (what this calculator models), biweekly payments (26 half-payments ≈ one extra full payment a year), or an annual lump sum from a bonus or tax refund. All shorten the term; the more you add and the earlier you start, the bigger the saving.
Before you prepay
Check that your loan has no prepayment penalty and that your servicer applies extra money to principal, not next month’s payment. Then weigh it against other uses of the cash — paying down a 6.5% mortgage is a guaranteed 6.5% return, but grabbing a full employer 401(k) match or clearing credit-card debt usually comes first.