Private, local mortgage planning
Model a fixed-rate mortgage, add extra payments, switch to bi-weekly payments, and compare up to five plans. The calculation runs entirely in your browser.
Private mortgage analysis
Start with the loan basics. Payment and amortization estimates exclude taxes, insurance, fees, and escrow.
Save the current inputs, then change the rate, term, frequency, or extra payment. Compare up to five plans side by side.
No saved scenarios yet. Add your current plan or try a preset.
| Scenario | Payment | Total interest | Payoff | Differences from A |
|---|
| Period | Payment | Principal | Interest | Balance |
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A fixed-rate mortgage payment is calculated from the loan principal, periodic interest rate, and total number of payments. This report estimates principal and interest only; taxes, insurance, escrow, and fees are not included.
An amortization schedule lists each loan payment and shows how much goes toward interest, how much reduces principal, and the remaining mortgage balance after the payment.
Extra payments reduce principal sooner. In the model, this lowers future interest charges and can shorten the payoff period. Confirm prepayment rules and processing details with your lender.
Explore these non-personal examples or use them as a starting point for your own comparison.
A fixed-rate payment is calculated from principal, the interest rate per payment period, and the number of payments. The scheduled principal-and-interest payment stays level, while its composition changes.
Early payments tend to contain more interest. As the balance falls, more of the same payment reaches principal.
Your inputs are passed directly to a Rust WebAssembly module in this page. The engine is deterministic, makes no external calls, and returns the schedule to your browser for the tables and charts.
Parameterized links on this page are generic examples. Copying a link is optional and happens only when you ask.
The calculator uses the standard fixed-rate amortization formula. It includes principal and interest, but not taxes, homeowners insurance, mortgage insurance, HOA dues, or lender fees.
An amortization schedule lists each payment and shows how it divides between interest and principal, along with the remaining balance after that payment.
Extra money is applied to principal in the model. That lowers the balance sooner, reduces future interest, and can shorten the payoff time. Confirm prepayment rules with your lender.
The bi-weekly model uses 26 equal payment periods per year and accrues interest for each of those periods. Lender programs can process bi-weekly payments differently, so compare the estimate with your loan terms.
No. Results are educational estimates. Rates, rounding, payment timing, escrow, fees, and lender rules can change real loan costs.
This calculator uses a fixed-rate, fully amortizing principal-and-interest model. It does not include property taxes, homeowners insurance, mortgage insurance, HOA dues, closing costs, or lender fees. Results are rounded to cents for display; internal calculations use floating-point precision. Confirm payment schedules, prepayment rules, and all figures with your lender.
Author and reviewer: Adriaan Greyling is a financial technology software engineer who has worked on transaction and credit-decisioning systems at large financial institutions since 1996. He does not hold financial planning, mortgage, lending, tax, or accounting credentials. His review covers the mortgage formula implementation, amortization behavior, and software calculations—not mortgage advice, underwriting, or lender verification.
Prepared and reviewed by Adriaan Greyling for MonkeyTactics. Last reviewed .
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