How do you use this tool?
- Enter the loan amount (e.g., $400,000 for a home purchase).
- Enter the annual interest rate (e.g., 6.75%).
- Set the loan term in years (e.g., 30 for a standard mortgage).
- Optionally enter a start date to see exact calendar payment dates.
- View the monthly payment amount and scroll through the full schedule.
What This Tool Does
This amortization calculator computes your fixed monthly payment and generates a complete schedule showing how each payment breaks down between principal and interest — for every period from the first payment to payoff.
How It Works
For a fixed-rate loan, the monthly payment is calculated using the standard annuity formula:
M = P × [r(1+r)^n] ÷ [(1+r)^n − 1]
Where:
- M = monthly payment
- P = principal (loan amount)
- r = monthly interest rate (annual rate ÷ 12)
- n = total number of payments (years × 12)
Each row in the schedule then calculates:
| Column | Formula |
|---|---|
| Interest payment | Remaining balance × monthly rate |
| Principal payment | Monthly payment − interest payment |
| Remaining balance | Previous balance − principal payment |
What Are Common Use Cases?
30-Year Fixed Mortgage. The most common US home loan. A $350,000 loan at 7.00% has a monthly P&I payment of $2,329. Over 360 payments, total interest paid is approximately $488,000 — nearly 1.4× the original loan.
15-Year Fixed Mortgage. Higher monthly payment ($3,145 at 6.50% on the same $350,000) but total interest of roughly $216,000 — a savings of over $270,000 compared to the 30-year at higher rate.
Auto Loan. A $35,000 car loan at 7.50% over 60 months yields a $700/month payment and $7,000 in total interest. Use the schedule to see your exact payoff balance at any point — useful if you plan to sell or trade in early.
Student Loan Repayment Planning. Federal student loan standard repayment is 10 years. On $50,000 at 6.54% (graduate Stafford rate, 2024), the monthly payment is $566 and total interest is $17,920.
Extra Payment Analysis. By adding an extra principal payment each period, you shorten the schedule. The tool recalculates the remaining balance row-by-row so you can see exactly which month the loan pays off.
How Do You Read the Amortization Schedule?
| Period | Payment | Interest | Principal | Balance |
|---|---|---|---|---|
| 1 | $2,594 | $2,250 | $344 | $399,656 |
| 12 | $2,594 | $2,248 | $346 | $395,815 |
| 120 | $2,594 | $2,205 | $389 | $362,831 |
| 240 | $2,594 | $2,049 | $545 | $336,555 |
| 360 | $2,594 | $14 | $2,580 | $0 |
Example: $400,000 loan, 6.75% annual rate, 30-year term.
Notice how the interest column declines gradually while the principal column grows — the crossover point where principal exceeds interest occurs around payment 252 (month 21 of year 21) for this example.
Frequently Asked Questions
Can I use this for adjustable-rate mortgages (ARMs)? This tool calculates fixed-rate schedules. For ARMs, the rate resets periodically — run separate calculations for each rate period and manually chain the results, using the end balance of one period as the principal for the next.
What is a balloon payment loan? A balloon loan has lower regular payments followed by one large final payment. This calculator assumes full amortization (balance reaches zero at the last regular payment). Balloon loans require a different calculation.
How accurate is the schedule? Results match standard US lending calculations within a few cents per period due to rounding conventions. Lenders may round differently on individual statements, but total interest figures will be very close.
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