Loan Payment Calculator
Calculate a required installment loan payment and see how optional extra monthly payments can shorten the payoff timeline and reduce total interest. Useful for personal loans, auto-style installment examples, and other fixed-term debts when you supply the APR and term.
Your results will appear here
Enter your assumptions and calculate to see the estimated result and supporting details.
How this calculator works
Enter loan amount, APR, term (months or years), optional extra monthly payment, and an optional first payment date for an estimated payoff calendar date.
Results compare the contractual baseline schedule with an accelerated schedule when extra payments are greater than zero.
Formula / methodology
M = P × [r(1+r)^N] / [(1+r)^N − 1] (for r = 0: M = P / N)
- Extra payment is applied to principal after interest each month.
- Schedules use the same cents-based amortization policy as the mortgage calculator.
- Payoff date estimation uses your optional first payment date and does not depend on today’s date for payment math.
- Calendar payoff dates preserve day-of-month when possible; otherwise they clamp to the last day of the target month (for example Jan 31 → Feb 28/29).
Worked example
A $20,000 loan at 8% APR for 60 months has a required payment of about $405.53.
Adding $100 extra each month can shorten payoff to about 47 payments and save roughly $1,036 in interest under the documented cents policy.
Important assumptions
- APR is treated as a nominal annual rate compounded monthly for installment math.
- Extra payments are assumed constant each month until payoff.
- Estimated payoff dates use month-end clamping when the original day does not exist in the target month.
- Fees, insurance products, and prepayment penalties are not modeled.
Common questions
That is allowed. Extra amounts still apply to principal after interest, so payoff can occur much earlier.
Lenders may use different day-count conventions, rounding rules, or fee structures. This tool uses a transparent cents schedule policy.
No. Without it you still get months until payoff. With it, the calculator also shows an estimated calendar payoff date.