Installment Loan Calculator: Monthly Payment & Amortization

Use this free Installment Loan Calculator to find your monthly payment, total interest, and see a complete amortization schedule. Fully accessible (WCAG AA).

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Audit: Complete

Formula (LaTeX) + variables + units

This section shows the formulas used by the calculator engine, plus variable definitions and units.

Formula (extracted LaTeX)

\[M = P \frac{r(1+r)^n}{(1+r)^n - 1}\]

M = P \frac{r(1+r)^n}{(1+r)^n - 1}

Formula (extracted LaTeX)

\[M = 25000 \times \frac{0.00625 \times (1+0.00625)^{60}}{(1+0.00625)^{60} - 1}\]

M = 25000 \times \frac{0.00625 \times (1+0.00625)^{60}}{(1+0.00625)^{60} - 1}

Formula (extracted LaTeX)

\[M = 25000 \times \frac{0.00625 \times (1.45329...)}{(1.45329...) - 1}\]

M = 25000 \times \frac{0.00625 \times (1.45329...)}{(1.45329...) - 1}

Formula (extracted LaTeX)

\[M = 25000 \times \frac{0.009083...}{0.45329...}\]

M = 25000 \times \frac{0.009083...}{0.45329...}

Formula (extracted LaTeX)

\[M = 25000 \times 0.020038...\]

M = 25000 \times 0.020038...

Formula (extracted LaTeX)

\[M = \$500.95\]

M = \$500.95

Formula (extracted text)

$ M = P \frac{r(1+r)^n}{(1+r)^n - 1} $

Variables and units

P = principal (loan amount) (currency)
r = periodic interest rate (annual rate ÷ payments per year) (1)
n = total number of payments (years × payments per year) (count)
M = periodic payment for principal + interest (currency)
E = extra principal payment per period (currency)

Sources (authoritative):

Home — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/
Finance — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/finance
Loans & Debt — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/subcategories/finance-loans-debt
Loan Prepayment Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/loan-prepayment
Loan Comparison Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/loan-comparison
Personal Loan Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/personal-loan
Auto Loan Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/auto-loan
APR Calculator — calcdomain.com · Accessed 2026-01-19
https://calcdomain.com/apr

Changelog

Version: 0.1.0-draft
Last code update: 2026-01-19

0.1.0-draft · 2026-01-19

Initial audit spec draft generated from HTML extraction (review required).
Verify formulas match the calculator engine and convert any text-only formulas to LaTeX.
Confirm sources are authoritative and relevant to the calculator methodology.

Verified by Ugo Candido on 2026-01-19
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Formulas

(Formulas preserved from original page content, if present.)

Version 0.1.0-draft

Citations

Add authoritative sources relevant to this calculator (standards bodies, manuals, official docs).

Changelog

0.1.0-draft — 2026-01-19: Initial draft (review required).