How our calculations work
Every number on FetchCalc comes from plain, deterministic TypeScript running in your browser. There is no model guessing at your payment, no server call, and no stored data. Here is exactly what the code does.
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The payment formula
All installment calculators use the standard amortization formula: P = A · r / (1 − (1 + r)⁻ⁿ), where A is the amount financed, r is the periodic rate and n is the number of payments.
The monthly rate is the annual rate divided by 12 — the convention U.S. lenders use for monthly-pay installment loans. When the rate is 0% the formula is undefined, so we fall back to A ÷ n.
Schedules and rounding
Schedules are built month by month. Interest for the month is the outstanding balance times the monthly rate, rounded to cents; the rest of the payment reduces principal. The final payment is trimmed so the balance lands exactly on zero rather than a fraction of a cent either side.
Because every row is rounded the way a servicer rounds, totals are the sum of actual payments rather than a closed-form approximation. Expect pennies of difference from your lender's statement, not dollars.
APR estimation
The APR calculator solves for the monthly rate at which the present value of your payments equals the cash you receive after fees, using bisection to a tight tolerance, then annualizes it. It is an estimate for comparing offers, not a lender disclosure — regulated APR depends on which charges count as finance charges and on each lender's rounding rules.
Mortgage and home equity assumptions
Mortgage results split principal and interest from taxes, insurance, HOA dues and PMI. Escrow items are treated as level monthly amounts derived from the annual figures you enter; in reality they are re-assessed periodically. PMI is dropped once the balance falls below 80% of the original value — a common rule, not a universal one.
Home equity results apply your lender's combined loan-to-value ceiling to your own estimate of the property's value. A lender will use an appraisal or automated valuation instead.
Payoff and overpayment simulations
Payoff tools simulate forward one month at a time. If the payment you enter does not cover the interest accruing, we say the balance never clears rather than returning a meaningless number. Extra payments are applied to principal in the month they are made, and schedules are capped at 600 months.
What we deliberately do not model
Variable and adjustable rates, income-driven student loan plans, forgiveness programs, daily-accrual interest, late fees, insurance products, tax deductibility and credit decisions are all out of scope. Anything a lender can change after signing is something we cannot forecast honestly.
About Ask Fetch
The assistant does not compute your results. It reads the same deterministic engine and explains it in words, and when it cannot match your question it says so plainly rather than inventing an answer. No live AI model is connected unless one is explicitly configured.
Review and corrections
Formulas and explanatory copy are reviewed together, and the review date appears on every calculator page. If you find a result you believe is wrong, tell us what you entered and what you expected — we would rather fix the arithmetic than defend it.
FetchCalc is an independent calculator and educational service. We are not a lender, broker, or financial adviser, and nothing here is financial advice. Estimates are for planning only; your actual offer and payment will come from your lender.