Loan & Amortization Calculator
Monthly payment and a full amortization schedule for any loan.
Optional. Extra principal paid each month.
Monthly payment
- Total interest
- $318,861.58
- Total paid
- $568,861.58
- Number of payments
- 360
- Payoff time
- 30 yr 0 mo
Estimate. The final payment is adjusted so the balance closes to exactly zero.
How the loan calculator works
This tool models a fully amortizing loan: a fixed payment, made on a regular schedule, that pays the loan down to exactly zero by the end of the term. It returns the level payment, the total interest, the total paid, and a row-by-row schedule showing how each payment splits between interest and principal.
The level payment comes from the standard amortization formula M = P*r / (1 - (1+r)^-n), where P is the principal, r is the periodic rate (annual rate divided by payments per year), and n is the number of payments. The calculator then walks the schedule one period at a time: each month the interest is balance * r, the principal portion is M - interest (plus any extra payment), and the balance drops by that principal. Both the payment and each interest figure are rounded to the cent, and the final payment is adjusted so the balance closes at 0.00 rather than drifting a cent off. If the rate is 0%, the payment is simply P / n.
Worked example
A 20,000 loan at 6% annual rate over 60 months (5 years), paid monthly.
- Periodic rate:
r = 6% / 12 = 0.005 - Level payment:
M = 20000 * 0.005 / (1 - 1.005^-60) = 386.66
The first two months show how the split shifts:
| Month | Payment | Interest | Principal | Balance |
|---|---|---|---|---|
| 1 | 386.66 | 100.00 | 286.66 | 19,713.34 |
| 2 | 386.66 | 98.57 | 288.09 | 19,425.25 |
| 60 | 386.41 | 1.92 | 384.49 | 0.00 |
Month 1 interest is 20000 * 0.005 = 100.00. By month 60 almost the entire payment is principal, and the last payment is trimmed to 386.41 so the balance ends exactly at zero.
- Monthly payment: 386.66
- Total interest: 3,199.35
- Total paid: 23,199.35
Now add an extra 100 to every payment. The loan clears in 47 months instead of 60, total interest falls to 2,444.36, and you save 754.99 in interest.
How to use it
- Enter the principal (the amount actually borrowed, after any down payment).
- Enter the annual rate as a percent, for example 6 for 6%, not 0.06.
- Set the term in months (a 30-year loan is 360, a 5-year loan is 60).
- Add an extra payment to see how much time and interest you save by paying ahead.
- Set payments per year to match your cadence (12 monthly, 26 biweekly, 52 weekly).
- Read the schedule to see, for any month, how much of your payment is interest versus principal.
Limitations
This is an estimate, not financial advice. It assumes a fixed rate and equal scheduled payments, so it does not capture variable-rate adjustments, missed or late payments, fees, points, mortgage insurance, escrowed taxes and insurance, or interest that compounds on a different convention than your lender uses. Your lender’s rounding may also differ by a few cents per payment. Use the result to compare scenarios and understand the structure of a loan, and confirm exact figures with your lender before signing.
Frequently asked questions
Why is my total interest a little different from payment times months minus principal?
Each scheduled payment is rounded to the nearest cent, and so is the interest charged each month. The calculator sums those cent-rounded interest figures rather than using a single theoretical product, so the total reflects the actual schedule. The final payment is also trimmed slightly so the balance lands on exactly 0.00, which can shift the total by a few cents.
How do extra payments shorten the loan?
Any extra amount you add goes straight to principal, on top of the principal portion of your regular payment. That lowers the balance faster, so less interest accrues in every later month, which means more of each future payment attacks principal. The loan reaches zero before the original term, and the calculator stops the schedule on that earlier month.
What does a 0% rate do to the schedule?
With no interest the payment is simply the principal divided by the number of months (straight-line). Every payment is pure principal, total interest is zero, and total paid equals the amount borrowed.
Can I model biweekly or other payment frequencies?
Yes. Set payments per year to match your schedule (12 for monthly, 26 for biweekly, 52 for weekly). The calculator converts the annual rate into a per-period rate and amortizes on that cadence. Biweekly payments usually retire the loan faster because you make the equivalent of one extra monthly payment each year.
Is the first payment mostly interest?
On an amortizing loan, yes. Early payments are interest-heavy because interest is charged on the full outstanding balance. As the balance falls, the interest share shrinks and the principal share grows, so late payments are almost entirely principal.