About the Loan Amortization Schedule Generator

A loan's amortization schedule is the row-by-row breakdown of how each payment splits between interest and principal. Early on, most of your payment is interest; later on, almost all of it is principal. This tool generates the full schedule along with the headline numbers (total interest, total cost, payoff date, effective APR) and a chart of the balance curve.

The three tabs

• Schedule — one row per scheduled payment with period, due date, payment, principal, interest, extra principal, remaining balance, and cumulative interest/principal. Defaults to a 6-row "key periods" view (period 1, 25/50/75% mid-points, last); click "Show full schedule" to see every row with row virtualization so even 5,000-period loans render smoothly.
• Summary — the six headline numbers: level payment, number of payments, total interest, total cost, payoff date, and effective APR. When loan fees are entered, the effective APR is computed via internal-rate-of-return on the actual cash-flow stream (the same regulatory definition used on US Loan Estimates).
• Charts — an ECharts line chart with three series: Remaining Balance, Cumulative Principal, Cumulative Interest. Auto-themed for light and dark mode; legend toggles series visibility.

Three day-count conventions

A day-count convention is a standardized way to handle the length of each period and the denominator used to compute the per-period interest. The three conventions supported here match the most common US retail-loan conventions:

• Actual/365 (default) — actual calendar days over a 365-day year. The most common US mortgage convention.
• Actual/360 — actual calendar days over a 360-day year. Used by some commercial loans and money-market instruments; slightly increases the effective interest rate.
• 30/360 (Bond Basis) — every month is treated as 30 days, every year as 360. The US corporate bond convention.

With the nominal-rate convention (the standard US mortgage/auto-loan approach), the APR you enter is divided by the number of payments per year to get the periodic rate, and the per-period interest is balance × (APR / paymentsPerYear). The day-count convention affects the schedule of due dates but not the level payment or total interest for a uniform-frequency loan.

Biweekly and weekly acceleration

Switching from monthly to biweekly gives you 26 payments per year instead of 12 — roughly one extra full payment per year. Most borrowers finish years earlier and save a substantial amount of interest, with no change to their budget beyond the timing. The Summary tab shows the actual (shorter) payoff date and payment count.

Extra payments

The Advanced disclosure holds two optional inputs: a recurring extra-principal amount applied every period, and a one-time extra-principal amount at a chosen period. Both shorten the loan and reduce total interest; the Summary tab reports the interest and periods saved compared to the base schedule.

Effective APR with fees

When you enter an origination fee (a fixed dollar amount applied at closing), the calculator computes the effective APR using internal-rate-of-return (IRR) on the actual cash flow: −(principal − fees) at time 0, then +payment for each scheduled period. The effective APR is higher than the nominal APR whenever fees are positive, and the difference is exactly what a US Loan Estimate would show.

Common use cases

• Comparing a 15-year vs. 30-year mortgage (use the term input with the years/months toggle).
• Estimating the impact of biweekly vs. monthly payments.
• Modeling a $100/month extra principal payment and seeing the interest saved.
• Computing the effective APR on a loan quote that includes origination fees.
• Verifying a loan officer's amortization schedule against a fresh calculation.

Educational only. Not financial advice.

All computation runs in the browser. No loan inputs, schedules, or results are sent to any server. The tool does not adjust for business-day calendars, weekends, or lender-specific payment-due dates — verify any real loan decision with your lender.