Every installment loan hides the same mechanic underneath its monthly bill: a fixed payment that covers more interest than principal at the start, then gradually flips so that more of each payment chips away at what you actually owe. This calculator makes that mechanic visible, month by month, and lets you test what happens if you add extra money on top.
This Calculator vs. the Mortgage Payment Calculator vs. the APR Calculator
This is the general-purpose amortization tool: it works for any fixed-rate installment loan, auto loans and personal loans included, and its focus is the month-by-month schedule, extra-payment modeling, and CSV export. Our Mortgage Payment Calculator is the mortgage-specific version, built around the extra costs particular to home loans, such as property tax and insurance escrow, that this calculator does not attempt to model. Neither tool tells you the true cost of borrowing when a loan carries origination fees or points on top of its stated interest rate; for that, the APR Calculator converts the rate plus fees into a single annual percentage rate so you can compare loan offers on equal footing before you ever get to the amortization stage.
Worked Example: The Calculator's Own Defaults
Leave the calculator at its starting values, a $200,000 loan at 5% for 30 years with no extra payments, and the standard amortization formula, M = (P × r × (1 + r)n) / ((1 + r)n - 1), produces a monthly principal-and-interest payment of $1,073.64. Run that payment for all 360 months and you pay $186,511.57 in total interest, for a grand total of $386,511.57 paid back on a $200,000 loan.
Now add a $200 extra payment starting in month 1. The required $1,073.64 payment does not change, but the extra $200 goes straight to principal every month, and the loan pays itself off in 256 months (about 21.3 years) instead of 360. Total interest drops to $125,351.06, a savings of roughly $61,160, in exchange for paying about 8.7 years sooner. That trade-off, less total interest against less flexibility with your cash, is exactly what the "with extra" and "without extra" comparison in this calculator is built to show.
Frequently Asked Questions
- Q: If I add extra payments from month 1, does my required monthly payment change?
- No. The required principal-and-interest payment is fixed for the full term. Extra payments only shrink the balance faster, ending the loan early instead of lowering what you owe each month.
- Q: Why does the "without extra" line matter if I always plan to pay extra?
- It quantifies exactly how many months and how much interest those extra payments are saving you, which is useful when deciding whether to prioritize this loan over other debt or investing.
- Q: Can extra payments start partway through the loan instead of month 1?
- Yes. Each extra payment entry has its own starting payment number, so you can model a raise or bonus that only begins later, rather than assuming it was available from day one.
- Q: Does choosing bi-weekly or weekly frequency change the schedule shown?
- Not yet. The frequency selector is informational; the detailed schedule and totals are always calculated monthly regardless of which option is selected.
Further Reading
- Investopedia - Amortization Definition & Examples
- Consumer Financial Protection Bureau - Understanding Loan Options
Disclaimer: This calculator and guide are for educational purposes only and should not be considered financial advice. Actual loan terms, fees, and prepayment rules vary by lender, so confirm the details of your own loan with your lender before making extra-payment decisions.