Monthly Payment Calculator
The Payment That Stays Fixed While Its Composition Shifts
A fixed-rate loan's monthly payment doesn't change over its term, but what that payment is made of does — early payments are mostly interest, later payments are mostly principal. This calculator computes the fixed payment amount itself using the standard amortization formula, along with the total interest that fixed payment adds up to over the full loan term.
The Formula
P is the loan amount (principal), r is the monthly interest rate (annual rate divided by 12), and n is the total number of monthly payments (years times 12). The formula solves for the fixed monthly payment that fully amortizes the loan — pays off both principal and interest — over exactly n payments.
Where This Matters
- Mortgage and auto loan budgeting — knowing the exact monthly payment before applying lets you check it against your budget or DTI limits ahead of time.
- Comparing loan terms — a 15-year term carries a higher monthly payment than a 30-year term on the same loan amount, but sharply lower total interest — this calculator makes both figures explicit.
- Rate shopping — even a small difference in quoted interest rate compounds into a meaningfully different payment and total interest cost over a multi-decade term.
Worked Example
| Metric | Value |
|---|---|
| Number of payments | 360 |
| Monthly payment | $1,896.20 |
| Total paid over term | $682,633.47 |
| Total interest paid | $382,633.47 |
On this loan, total interest paid over 30 years exceeds the original loan amount — a common outcome for long-term, moderate-rate mortgages.
How to Use This Calculator
- Enter the loan amount.
- Enter the annual interest rate.
- Enter the loan term in years.
- Select Calculate to get the monthly payment, total amount paid, and total interest.
Related Calculations
See the full year-by-year breakdown with the Loan Amortization Calculator, or check what payment your income supports with the Mortgage Affordability Calculator.