Mortgage Calculator

WHAT IT DOES

Mortgage Calculator helps you understand the full cost of buying a home. Enter the home price, down payment, annual interest rate, and loan term in years. The panel instantly shows your loan-to-value ratio, loan amount, monthly principal and interest payment, property tax, insurance, and total monthly payment. The comprehensive amortization schedule breaks down every monthly payment into principal, interest, tax, and insurance components, showing exactly how your balance decreases over time. This complete picture helps you make informed decisions about home affordability, down payment strategies, and loan term choices.

WHERE IT RUNS

This script runs on every website you visit. Whether you are researching homes on real estate portals, comparing mortgage rates on bank websites, planning a purchase with a financial planner, or evaluating refinancing options, the panel is always available. It works alongside your existing tools without interfering with your workflow.

HOW TO USE

Enter the home price and down payment amount in the first two fields. Enter the annual interest rate as a percentage and the loan term in years. Optionally add property tax and home insurance rates as percentages of the home value per year. Results update automatically as you type. Click "Show Amortization Schedule" to see a detailed breakdown of each monthly payment, including how much goes toward principal, interest, taxes, and insurance. The schedule displays the first 60 months, with an indicator for any remaining months. Click any history entry to reload previous calculations for quick comparisons. Use the "Copy Result" button to copy the total monthly payment and loan-to-value ratio to your clipboard.

THE LOAN-TO-VALUE RATIO MECHANISM

Mortgage Calculator provides a critical metric that many simple calculators omit: the loan-to-value (LTV) ratio. LTV is calculated as (loan amount ÷ home price) × 100% and is a key factor in mortgage approval, interest rates, and private mortgage insurance requirements. The calculator computes LTV in real-time as you adjust the down payment, showing you exactly how your down payment affects your loan position. The amortization schedule includes property tax and insurance alongside principal and interest, giving you a true "total payment" view that matches what you would pay into an escrow account with a real mortgage servicer.

THE PANEL

The panel is fully draggable and remembers its position per site. It minimizes to a compact floating bubble when collapsed. All settings — default interest rate, default loan term, default tax rate, default insurance rate, and calculation history — persist across browser sessions using GM_setValue storage. Press the Escape key to close the panel. The panel automatically focuses the home price input field for quick keyboard entry.

PLEASE NOTE

This script requires the free BotGentz extension to run. The calculations are estimates based on standard mortgage amortization formulas — actual loan terms, fees, and insurance requirements vary by lender, location, and specific conditions. Always verify with your financial institution before making decisions. Tax and insurance estimates are simplified — actual rates vary by location and property. Websites change their structure and behavior over time; if any functionality stops working, the script may need an update. No user data is sent anywhere — all calculation history and settings are stored locally in your browser. The script never reads or modifies password, hidden, or file input fields.