Enter a loan amount, rate, and term, and this calculator does two things at once: it computes your required monthly payment using the standard amortization formula, and it simulates that loan month by month twice — once as scheduled, and once with any extra payment you specify applied straight to principal — so you can see the payoff gap between the two side by side.
The Payment Formula, Applied to Your Numbers
The monthly payment comes from M = P × [i(1+i)n] ÷ [(1+i)n − 1], where P is the loan amount, i is the monthly interest rate (annual rate ÷ 12), and n is the total number of monthly payments. From there, the calculator walks forward one month at a time: it charges interest on whatever balance remains, applies the rest of the payment to principal, and carries the new, smaller balance into the next month. That loop is what builds the full amortization table below, and running it twice — with and without your extra payment — is what produces the comparison.
What You're Looking At: Two Schedules, One Chart
- Summary Comparison: total principal, total interest, total paid, and months-to-payoff for both the standard and extra-payment paths.
- Balance Comparison Chart: the two remaining-balance curves plotted together, so the gap between them visually grows the longer the loan runs.
- Detailed Amortization Schedule: the month-by-month principal/interest/balance breakdown for the extra-payment scenario, exportable as CSV.
Mortgage Payment vs. Rent-vs-Buy vs. a Plain Amortization Table
This calculator tells you what a specific loan will cost and how extra payments change that cost — it doesn't tell you whether buying beats renting in the first place. That's a separate, bigger question involving opportunity cost, appreciation assumptions, and how long you'll stay; the Rent vs. Buy Calculator is built for that comparison. And if you've already settled on a loan and just want the raw month-by-month ledger without the extra-payment scenario layered in, the standalone Loan Amortization Calculator gives you that table on its own for any type of installment loan, not just a mortgage.
A Note on What's Not Modeled Yet
Property taxes, homeowners insurance, PMI, and HOA dues aren't part of this payment figure — it's the principal-and-interest portion only. If your lender quotes a monthly figure that includes those escrow items, expect this calculator's number to come in lower than that quote, by design.
Further reading: Investopedia — Mortgage Calculator and Wikipedia — Mortgage Calculator.
Disclaimer: This calculator and the notes above are for educational purposes only and should not be considered financial advice. Actual loan terms, taxes, and insurance costs vary by lender and location. Always consult a qualified mortgage professional or financial advisor before making borrowing decisions.