See how extra payments, biweekly payments, or paying the remaining balance in full change the payoff date and total interest. Enter the original loan (or the unpaid principal from a statement), pick a repayment option, and compare the scheduled loan with the faster path — including an expandable amortization table.
Formula
The scheduled monthly P&I on principal P, monthly rate i = R / 1200, and N months is:
payment = P × i / (1 − (1 + i)^(−N))
Known remaining term. After k = Norig − Nrem payments the remaining balance is the present value of the remaining original payments. Extra amounts are added on top of that contractual payment starting now; a yearly extra lands at the end of each remaining year, and a one-time extra with the first remaining payment.
Unknown remaining term. Given unpaid principal and the statement payment, the remaining months are however many it takes that payment to clear the balance (the last month may be partial).
Biweekly. Half the monthly payment every two weeks is modeled as monthly compounding plus an extra half-payment every six months — 26 half-payments a year, equal to one extra monthly payment.
Each month: interest = balance × i, then principal = payment − interest (plus extras). The final payment clears whatever is left.
Payoff options at a glance
| Option | What you pay | Typical effect |
|---|---|---|
| Extra payments | Scheduled P&I plus monthly, yearly, and/or one-time extras | Shorter term, large interest cut |
| Biweekly | Half the monthly P&I every two weeks | About one extra month per year |
| Altogether | Remaining balance as a lump sum | No further interest |
| Normal | Scheduled monthly P&I only | Baseline for comparison |
Examples
$400,000 · 30 years · 6% · 25 years left · $500 extra per month
After five years the remaining balance is $372,217.43. Adding $500 to the $2,398.20 P&I pays the loan off in 17 years and 3 months — 7 years and 9 months earlier — and saves about $122,306 in interest (~26% less interest, ~31% faster).
Same loan, biweekly instead of extra monthly
Half of $2,398.20 is a $1,199.10 biweekly payment. Payoff drops to 21 years and 2 months (3 years 10 months earlier) with about $61,869 of interest saved.
Statement only: $230,000 unpaid · $1,500 monthly · 6%
The remaining term is 24 years and 4 months. An extra $500 per month clears it in 14 years and 4 months (10 years earlier) and cuts remaining interest from $207,677.36 to $113,122.63.