Mortgage Calculator

Same numbers, programmatically. This page runs entirely in the browser; the same engine is also available as a JSON API and MCP server (see llms.txt). The calculation is a standalone, dependency-free script that works in Node or a browser: https://www.a3sec.net/tools/engines/mortgage-engine.js. Example: curl -sO https://www.a3sec.net/tools/engines/mortgage-engine.js && node -e "const M=require('./mortgage-engine.js');console.log(JSON.stringify(M.summarize(M.quickQuote({country:'CA',region:'ON',price:700000,downPct:10})),null,1))"

Prefill by URL: mortgage.html?country=CA&region=ON&price=700000&down=10&apr=4.5&years=25&extra=200&agent=1. Parameters: country (US|CA), region (TX CA NY FL NC | AB ON BC), price, down (percent) or downAmount, apr, years or months, taxYearly, insuranceYearly, hoa, utilities, extra, homeStartEligible (yes|no|unknown), lang (en|uk), theme (dark|light); agent=1 opens this panel. Results appear below as JSON (element id resultsJson).

Model. Standard amortization. US compounds monthly; Canada semi-annually ((1+APR/2)^(1/6) − 1). US PMI: 1.35 / 0.85 / 0.50% of the loan per year for under 5 / 10 / 20% down, terminated on the original schedule at 78% LTV or the term midpoint, assuming payments are current; early cancellation by request is not modeled. Canada CMHC: 4.00 / 3.10 / 2.80% one-time premium for 5–9.99 / 10–14.99 / 15–19.99% down, financed into the loan, plus 0.20 percentage points for eligible amortizations over 25 years (maximum 30 years); minimum down payment 5% of the first $500k plus 10% of the rest, 20% at $1.5M+. Property-tax presets (% of price per year, approximate 2024–25 averages): TX 1.63, CA 0.72, NY 1.50, FL 0.83, NC 0.76, AB 0.72, ON 0.95, BC 0.42. Cash at closing = down payment + transfer taxes (Ontario LTT and BC PTT brackets, Alberta registration fees; NY 1% mansion tax at $1M+; FL 0.55% of the loan) + Ontario 8% PST on the CMHC premium + other costs (US 4%, Canada 1.5% of price). Money is in the local currency (USD / CAD).

Average rates. https://www.a3sec.net/tools/data/rates.json holds the current averages used as APR presets: US 15- or 30-year fixed matched to the loan term (Freddie Mac PMMS via FRED series MORTGAGE15US / MORTGAGE30US, refreshed when the site is deployed) and Canada 5-year fixed for a high-ratio mortgage, posted 5-year and estimated variable (Bank of Canada Valet API series FVI_MTG_RATE_5Y_FIX, V80691335, BROKER_AVERAGE_5YR_VRM, which this page also refreshes live). The APR field is filled from these until you type your own rate.

No code execution? The same calculation is available as a JSON API (https://www.a3sec.net/api) and as MCP tools at https://www.a3sec.net/api/mcp. All three calculators are described in https://www.a3sec.net/llms.txt. Estimates only — not financial advice.

Current results (JSON, updated on every calculation):

{}