Loan Interest Calculator
Calculate your monthly payment, total cumulative interest, and full amortization schedule. See exactly how extra payments shrink your interest bill and shorten your loan.
Loan Interest Calculator
Even small extra payments can save thousands in cumulative interest.
Monthly Payment
$1,580.17
Total Interest
$318,861
Total Paid
$568,861
Payoff Time
30.0 yrs
Balance vs Cumulative Interest
Amortization Schedule
The loan amortization formula
Standard fixed-rate loans use this monthly-payment formula:
M = P × [r(1 + r)^n] / [(1 + r)^n − 1]
where P is the loan principal, r is the monthly interest rate (annual ÷ 12),
and n is the total number of payments. Cumulative interest = (M × n) − P.
Why extra payments work so well
Every extra dollar applied to principal reduces the balance interest is calculated on for all future months. The savings compound — meaning a $100 extra payment in year 1 saves far more than a $100 extra payment in year 25. This is why even tiny early-loan extras have an outsized effect.
Strategies to lower cumulative interest
- Bi-weekly payments. Splitting one monthly payment into two bi-weekly halves results in 13 monthly payments per year — saving years of interest.
- Round up. Paying $1,500/month instead of $1,432/month painlessly chips away at principal.
- Apply windfalls. Bonuses and tax refunds applied directly to principal can eliminate entire years of payments.
- Refinance when rates fall. Lower rate × same payment = principal pays down faster.