Calculator
Example data table
| Input | Value | Notes |
|---|---|---|
| Loan amount | 250,000 | Principal borrowed |
| Annual rate | 6.50% | Fixed rate |
| Term | 30 years | Monthly payments |
| Extra per payment | 50 | Principal reduction |
| First payment date | 2026-05-11 | Example start |
| # | Date | Payment | Principal | Interest | Extra | Balance |
|---|---|---|---|---|---|---|
| 1 | 2026-05-11 | 1,630.17 | 276.00 | 1,354.17 | 50.00 | 249,724.00 |
| 2 | 2026-06-11 | 1,630.17 | 277.50 | 1,352.67 | 50.00 | 249,446.50 |
| 3 | 2026-07-11 | 1,630.17 | 279.00 | 1,351.17 | 50.00 | 249,167.50 |
Formula used
Periodic rate
If the annual nominal rate is APR and payments per year are m, then:
Regular payment (fixed-rate phase)
For principal P, periodic rate r, and n payments:
Per payment breakdown
When a rate change begins, the calculator re-amortizes the remaining balance across remaining payments.
How to use this calculator
- Enter the loan amount, annual interest rate, term, and first payment date.
- Choose a payment frequency to match your lender schedule.
- Add extras (per payment, yearly, or one-time) to see payoff changes.
- If your rate can change, fill up to three rate-change rows.
- Press Calculate schedule to view results above the form.
- Use Download CSV or Download PDF to export your schedule.
Payment composition shifts over time
Early payments are interest-heavy because interest is calculated on the highest balance. For a $250,000 loan at 6.50% over 30 years with monthly payments, the scheduled payment is about $1,580.17. In month one, interest is roughly $1,354.17 and principal about $226.00 (before extras). As the balance declines, interest falls and principal rises, accelerating equity build-up later.
Extra payments change both term and cost
Extra principal reduces the balance immediately, shrinking future interest charges. Adding $50 per month to the same example can shorten payoff from 360 payments to about 329 payments, saving roughly $32,900 in interest. Lump sums work similarly: a one-time $5,000 extra early usually saves more than the same amount near the end.
Frequency affects cash flow and total interest
Weekly and biweekly schedules use smaller, more frequent payments and a periodic rate based on payments per year. When the total paid per year is higher than the monthly equivalent, the loan can retire earlier. Many borrowers choose biweekly because 26 payments can feel like “13 monthly” payments across a year. The schedule table helps you match payments to payroll timing and see the balance path for each cadence.
Interest-only periods require a reset plan
During an interest-only phase, payments cover interest and the balance stays flat unless you add extra principal. When amortization begins, the remaining balance must be repaid over fewer payments, so the scheduled payment typically jumps. Model different interest-only lengths to measure that jump and test mitigation with extras.
Rate changes and scenario comparisons
If the annual rate changes at a specific payment number, the schedule re-amortizes the remaining balance across the remaining term. For example, moving from 6.50% to 7.50% at payment 25 recalculates the payment for the remaining term and increases total interest unless offset by extra principal. Export CSV/PDF and compare total interest, payoff date, and ending balance. Even a 1.00% rate increase early can add tens of thousands in interest, depending on term and extras.
FAQs
1) What does “regular payment” represent?
It is the scheduled payment used after any interest-only period. It is recalculated when a rate change starts so the remaining balance amortizes over the remaining payments.
2) Why can monthly, biweekly, and weekly totals differ?
The periodic rate is APR divided by payments per year. More frequent payments can reduce interest faster if they increase total annual paid, but the exact impact depends on your chosen cadence and extras.
3) How are extra payments applied?
Extras are treated as additional principal. They reduce the balance immediately, which lowers future interest. Extras are capped so the balance never goes below zero on the final payment.
4) What happens during an interest-only period?
Each payment covers interest for that period, so scheduled principal is zero. If you add extras, they still reduce principal. When amortization begins, the payment usually increases because fewer payments remain.
5) How do rate changes work in this schedule?
Enter a payment number and a new annual rate. Starting on that payment, the periodic rate updates and the calculator re-amortizes the remaining balance across the remaining term, keeping the schedule consistent.
6) Why might my lender’s amortization differ slightly?
Lenders may use different day-count conventions, rounding rules, or payment application order. This tool uses a nominal APR divided by payments per year and optional rounding to cents for a clear, comparable schedule.