Calculate monthly mortgage payments with detailed amortization schedule, extra payment impact, and interest savings visualization.
On many longer-term mortgages, the balance falls slowly at first because each level payment initially contains more interest than principal. This calculator determines the monthly principal-and-interest payment from the loan amount, annual interest rate, and term, then shows how the balance changes through the amortization schedule. It can also compare the scheduled payoff with added principal payments and display the resulting reduction in interest and payoff time. The result users most often misread is the monthly payment: principal and interest are not necessarily the complete housing payment, which may also include taxes, insurance, and association charges.
A concrete input and expected output from the current implementation.
Input
Loan amount: $100,000 Annual interest rate: 6% Loan term: 30 years Extra monthly payment: $0
Expected output
Monthly principal-and-interest payment: $599.55. First scheduled payment: $500.00 interest, $99.55 principal, and a remaining balance of $99,900.45.
The monthly rate is 0.5 percent, so the first month's interest is $100,000 multiplied by 0.005, or $500.00. Subtracting that interest from the unrounded fixed payment leaves about $99.55 for principal.
For a positive interest rate, the calculator applies the standard level-payment amortization relationship to the starting mortgage balance, the monthly rate, and the number of monthly payments. The monthly rate is the entered annual rate divided by 12, while the payment count is the term in years multiplied by 12. This models a fully amortizing, fixed-rate mortgage with monthly payments.
Each schedule row calculates interest on the unpaid mortgage balance for that payment period. The regular payment first covers that interest, and the remainder reduces principal. An entered extra payment is applied as additional principal, lowering the balance used for later interest calculations. The comparison reports the modeled earlier payoff and interest savings relative to the same mortgage without extra payments.
Usually no for a standard fixed-rate mortgage. Extra principal reduces the balance and can shorten the modeled payoff period, but the contractual monthly principal-and-interest payment normally remains unchanged. A lender-approved recast can reduce later required payments, but this calculator's extra-payment comparison should not be read as approval or confirmation of a recast.
The lender's estimate may include escrowed property taxes, homeowners insurance, mortgage insurance, or other charges, while the amortized payment may cover only principal and interest. Differences can also arise from the rate entered, first-payment timing, daily-interest treatment, payment rounding, or loan-specific terms. The calculator cannot reproduce terms that were not entered.
The example and behavioral notes were checked against the browser implementation. Standards and primary references below define the relevant format, formula, or platform behavior.
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