Last updated October 13, 2026 · Report an error
A loan's monthly payment isn't obvious from the interest rate alone — the term, the principal and how interest compounds over time all interact. This calculator takes your loan amount, annual interest rate and term, and works out the exact monthly payment using the standard amortization formula lenders use, along with the total interest you'll pay over the life of the loan and the full month-by-month schedule.
It also handles one thing most simple calculators skip: paying extra toward the principal each month. Add an extra monthly amount and the calculator shows exactly how many months sooner you'd be debt-free and how much interest that extra payment actually saves — often a surprisingly large amount on longer loans.
How it works
Enter the loan amount, the annual interest rate, and the term in months (360 for a 30-year mortgage, 60 for a 5-year auto loan, and so on). Optionally add an extra monthly payment amount to see an accelerated payoff scenario. The calculator computes the standard monthly payment, then simulates the full amortization schedule month by month to show exactly how much of each payment goes to interest versus principal, and the remaining balance after each one.
- Enter the loan amount, annual interest rate and term in months.
- Optionally add an extra monthly payment to model an accelerated payoff.
- Review the monthly payment, total interest and payoff time.
- Generate the full month-by-month amortization schedule and download it as a PDF.
Examples
30-year mortgage
A $200,000 mortgage at 6% annual interest over 360 months comes to a monthly payment of $1,199.10, with total interest over the full term of $231,677.05 — more than the original loan amount, which is typical for long-term, lower-rate mortgages.
Auto loan with extra payments
A $25,000 auto loan at 7% over 60 months has a standard payment of $495.03/month and $4,701.82 in total interest. Adding $100 extra per month pays the loan off 11 months early and cuts total interest to $3,762.80 — nearly $1,000 saved from a $100/month habit.
Who should use it
- Comparing monthly payments and total interest across different loan offers.
- Estimating a mortgage, auto loan or personal loan payment before applying.
- Modeling how extra monthly payments would shorten a loan and reduce interest.
- Understanding how much of an early payment goes toward interest versus principal.
Industry applications
- Mortgage and home buying
- Auto financing
- Personal and student loans
- Small business loans
Advantages
- Uses the same standard amortization formula real lenders use.
- Models extra monthly payments and shows the actual time and interest saved.
- Produces a full month-by-month schedule, not just a single payment figure.
Limitations
- Principal and interest only — doesn't include taxes, insurance, PMI or fees.
- Assumes a fixed rate for the full term; doesn't model adjustable-rate loans.
- Extra payments are modeled as a constant monthly amount, not one-off lump sums.
Common mistakes to avoid
- Comparing loans by monthly payment alone instead of total interest paid over the full term.
- Forgetting that a lower monthly payment from a longer term usually means paying significantly more total interest.
- Not accounting for taxes, insurance, or fees that many real loan payments include on top of principal and interest.
- Assuming extra payments only help at the end of a loan — they generally help most when made early, while more of the balance is still accruing interest.
Best practices
- Compare total interest paid, not just the monthly payment, when evaluating different loan terms.
- Run the numbers with a realistic extra-payment amount you can sustain, not an optimistic one-time figure.
- Recalculate whenever the rate or term changes — even a small rate difference compounds significantly over a long term.
- Use the amortization schedule to understand how much of your early payments goes to interest versus principal.
Tips
- If comparing multiple loan offers, run each through the calculator with its exact rate and term to compare total interest, not just the advertised payment.
- Even a modest extra payment made consistently from the start of a long-term loan tends to save more than the same extra amount added later.