Get the weekly radar
One short email with the freshest products, every week.
Grounded in available product and source data
A free, privacy-respecting, browser-based car payment calculator for U.S. auto loans. Real-time monthly payment estimates with credit-tier APR defaults, accurate state-level vehicle tax handling (including trade-in credit rules and the South Carolina IMF cap), full amortization schedules, and a side-by-side term comparison from 24 to 84 months.
Live site: carpaymentcalculator.app Embed widget: carpaymentcalculator.app/embed.html Trust & transparency: carpaymentcalculator.app/legal.html
This project is also commonly searched as a car loan calculator or auto loan calculator — the underlying math is identical; the names are interchangeable.
Most online auto loan tools are built for ad revenue first and accuracy second. They typically:
The Car Payment Calculator takes the opposite stance: zero tracking, zero ads, zero signup, fully client-side, and a tax engine that actually models how each state computes vehicle sales tax. See the methodology section for full data sources and known limitations.
update() function that owns all DOM writes.| Mode | What you enter | What you get |
|---|---|---|
| I know the price (Forward mode, default) | Vehicle price, down payment, trade-in, credit tier or APR, loan term, ZIP / tax rate | Monthly payment, total interest, full amortization |
| I know my budget (Reverse mode) | Monthly budget, down payment, trade-in, credit tier or APR, loan term, ZIP / tax rate | Maximum affordable vehicle price |
Reverse mode is uncommon among free car loan calculators — most tools only run forward. The math uses a closed-form solution to the standard amortization equation; see methodology.
The ZIP-to-state tax router is a two-tier lookup defined in index.html as STATE_RULES, ZIP2_TO_STATE, and ZIP3_OVERRIDES. Coverage:
Each state rule encodes:
For users in major metros where county and city taxes add 0.5–4% on top of the state rate, the calculator displays a static hint pointing them to override the rate manually with their actual local figure. Examples surfaced in the UI: NYC ≈ +4.9%, Chicago ≈ +4%, Los Angeles ≈ +2.5%, Seattle ≈ +3.6%.
Full coverage and known limitations are documented on the methodology page.
A standalone, minimal embeddable build of the calculator lives at carpaymentcalculator.app/widget.html. It's designed for credit unions, schools, financial-aid offices, personal-finance bloggers, and auto dealers who want to add a free car payment calculator to their own site.
The widget accepts three optional URL query parameters:
| Parameter | Example | Effect |
|---|---|---|
accent |
?accent=%23004488 |
Replace the default coral accent with any hex color (URL-encoded #); strict regex validation prevents CSS injection |
defaultApr |
?defaultApr=4.99 |
Pre-fill the APR field with your lender's actual rate |
taxRate |
?taxRate=8.875 |
Pre-fill the sales tax rate (e.g., for a region-specific embed) |
<iframe src="https://carpaymentcalculator.app/widget.html?accent=%230066CC&defaultApr=5.99" width="100%" height="620" style="border:none; max-width:480px; border-radius:16px;" title="Car Payment Calculator" loading="lazy"></iframe> <p style="font-size:12px; color:#777; text-align:center; margin-top:6px;"> Calculator by <a href="https://carpaymentcalculator.app/" target="_blank" rel="noopener">carpaymentcalculator.app</a> </p>
The interactive embed builder provides a live preview, color picker, and copy-paste snippet generator.
The attribution <a> tag is intentionally placed outside the iframe in the snippet because Google does not consistently count in-iframe links as backlinks to the iframe source. Embedders can keep both the inside-widget badge and the outside-iframe attribution, or strip just the inside one — the outside link is what passes link equity to the main site.
widget.html itself is served with <meta name="robots" content="noindex, follow"> plus a canonical link back to the main domain, so the widget never competes with the main page for search rankings.
The entire user-facing application is a small constellation of static HTML files with inline CSS and JavaScript. There is no build step, no bundler, no JavaScript framework, and no server. The trade-off:
| Pros | Cons |
|---|---|
| Zero deploy complexity (drop files on any static host) | Some CSS is duplicated across pages |
| Immediate page paint, no JS framework cost | No automatic code splitting |
| Easy to fork and host elsewhere | Larger single files for the main app |
| First-paint perceived latency under 200ms on broadband | Reading the source requires scrolling |
For a tool whose entire value lives in fast first interaction, this trade-off is correct. See the tech stack section for specifics.
<style>, all JS in <script>, all SVG inlinedisplay=swapThe single external dependency is Google Fonts. Self-hosting the WOFF2 files is on the roadmap but not yet implemented.
carpaymentcalculator/
├── index.html # Main calculator (HTML + CSS + JS, all inline)
├── widget.html # Minimal embeddable build (lite UI, 3 query params)
├── embed.html # Marketing landing page for the widget
├── legal.html # About + Methodology + Privacy + Disclaimer + Contact
├── favicon.svg # Hand-drawn SVG favicon (car + dollar circle)
├── og-image.png # Open Graph share image (1200 × 630)
├── robots.txt # Crawler rules
├── sitemap.xml # Lists /, /embed.html, /legal.html (widget.html intentionally excluded)
└── README.md
No build step required. Either:
# Option 1: open the file directly in a browser open index.html # macOS start index.html # Windows xdg-open index.html # Linux # Option 2: serve over a local HTTP server (recommended — proper MIME types, no file:// CORS quirks) npx serve . # or python3 -m http.server 8000
The ZIP code tax lookup runs entirely offline; all state-level tax rules are bundled inside index.html as JavaScript constants. No network requests are made when the calculator is in use beyond the initial page load and the Google Fonts CSS request.
Loan payments use the standard amortization formula:
M = P × r(1+r)ⁿ / ((1+r)ⁿ − 1)
where M is the monthly payment, P is the financed principal (purchase price minus down payment minus trade-in plus applicable tax), r is the monthly interest rate (APR / 12 / 100), and n is the number of monthly payments.
Reverse mode solves the same equation for P given a target M, with a closed-form derivation that accounts for trade-in credit rules and any applicable tax cap. The full derivation, data sources, and known limitations are documented on the methodology page.
APR defaults by credit tier are sourced from Bankrate's auto loan rate index and Experian's State of the Automotive Finance Market report, reviewed quarterly.
This free car payment calculator is fully client-side. Inputs never leave the browser; there is no backend server.
localStorage or sessionStorage is usedFull privacy stance is published at carpaymentcalculator.app/legal.html#privacy.
