How to use this calculator
Inspect how a fixed-rate loan balance changes from payment to payment. An amortization schedule separates principal repayment from interest, making the effect of extra payments and different payment frequencies visible.
Read the payment schedule
Interest for each period equals the opening balance multiplied by the nominal annual rate divided by payments per year. The regular installment covers that interest first; the remainder reduces principal. An extra payment is added to principal repayment each period.
Cumulative principal should equal the original loan amount when repayment finishes. Total payments equal principal plus total interest. Calculations retain full precision internally, so adding displayed amounts rounded to cents can produce a small rounding difference.
Frequency and date assumptions
The payment label follows the selected frequency; a weekly payment is not a monthly payment. Changing frequency recalculates equal installments over the term rather than keeping a monthly installment and splitting it into accelerated payments.
The date entered is the first-payment date. Monthly dates keep the same day where possible and use month-end when necessary. Weekly and biweekly dates advance by seven and fourteen days. Semimonthly dates alternate two monthly anchor days. These are estimated dates, without weekend, holiday or lender processing adjustments.
How do extra payments change an amortization schedule?
An extra payment reduces principal after the regular installment. Future interest is then calculated on a smaller balance, which can reduce total interest and shorten repayment. Compare two schedules with identical principal, rate and term, changing only the extra-payment amount.
The extra payment here applies each selected payment period. A $100 extra monthly payment and a $100 extra weekly payment are different annual commitments. This calculator assumes extra payments reduce principal and excludes prepayment penalties; confirm those terms with your lender.
Why does the interest portion fall over time?
With a fixed rate and regular payments, interest is calculated on the remaining balance. As principal is repaid, the balance falls, so less of a later installment goes to interest and more goes to principal. The scheduled installment can stay the same even though its two portions change.
Use the remaining-balance column to estimate the balance after a scheduled payment. A lender’s payoff quote may also include interest accrued between payment dates, fees or other adjustments that this schedule does not model.
Example: extra principal at zero interest
A $1,200 loan at 0% over one year has a $100 monthly installment. Adding $500 of principal each month produces two payments of $600 and no interest. The same zero-rate principal across 52 weekly periods has a regular payment of about $23.08.