Finance Toolkit › Free calculators

Loan Payoff Calculator with Extra Payments

See your monthly payment, total interest, and exactly how much time and interest an extra monthly payment saves.

The same calculation as an API

Building something? This page calls the same deterministic math the Finance Toolkit API exposes as JSON. Free tier, no signup, no key:

curl -s https://smeltworks.com/financetoolkit/v1/loan/amortization \
  -H 'content-type: application/json' \
  -d '{"principal":32000,"apr":6.4,"term_months":60,"extra_monthly":0,"include_schedule":false}'

See all endpoints and pricing →

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