How the answer is found
There is no simple formula for “extra payment to hit a date” once real amortization is involved, so this tool does not approximate. It searches. It runs your full month-by-month schedule against candidate extra payments. It narrows the range until it lands on the smallest amount that reaches zero by your target month.
The result is exact: one dollar less and the payoff slips past your date. The same search also finds the single lump sum that does the job, if you’d rather make one payment today than raise every month’s.
Figures are principal and interest only. Both answers assume your extra money goes straight to principal. Confirm that with your servicer, and check for prepayment penalties. For the full picture (lump sums in specific months, bi-weekly schedules, the payment table and CSV export) use the main payoff calculator. Your loan and goal inputs carry over.