Complete Mortgage Calculator

This is the multi-mode mortgage tool: Calculation Mode switches between four calculation paths (Payment, Affordability, Refinance, Rent vs Buy). Each mode's own fields — Current Loan Balance, Current Interest Rate, Current Monthly Payment, and Years Remaining on Current Loan for Refinance; Current Monthly Rent, Annual Rent Increase, Home Appreciation Rate, Investment Return Rate, and Years to Compare for Rent vs Buy — only appear (under "Show advanced options") once you switch Calculation Mode to the matching mode, since the engine ignores them in every other mode. Refinance has one further sub-gate beyond the mode switch: it is calculationMode === 2 AND currentLoanBalance > 0 (line 140) — since Current Loan Balance defaults to $0, switching Calculation Mode to "Should I Refinance?" alone is not enough to activate the refinance math; a non-zero Current Loan Balance is required too. Within Refinance mode, Current Interest Rate is a fallback, not a primary input: if you enter a non-zero Current Monthly Payment, that figure is used directly and Current Interest Rate is ignored; only when Current Monthly Payment is left at its $0 default does the calculator fall back to estimating your old payment from Current Interest Rate, Current Loan Balance, and Years Remaining on Current Loan.

PMI (Monthly PMI, PMI Required) is a genuine hard threshold, not a smooth curve: it switches on at 0.7% of the loan annually the instant Down Payment drops below 20%, and off entirely at 20% or above (line 90) — moving Down Payment from 22% to 18% around the default flips PMI from $0 to about $191/month, by far the largest swing any input produces on that output, purely because it crosses the threshold rather than because of a large underlying rate change. Down Payment moves Total Monthly Payment down by about 12% across a ±10% probe — a smaller share than Home Price's roughly 18% — a mix of the direct financed-amount reduction and, when it crosses the 20% line, the PMI switching off too. Annual Household Income never moves Total Monthly Payment, Monthly P&I, or any of the payment-calculation outputs — it's used only in the separate affordability math (Max Affordable Home, Max Monthly Payment), which the calculator runs unconditionally regardless of which mode is selected. This calculator does not account for mortgage points, an adjustable-rate structure, or state-specific PMI cancellation rules beyond the flat 20% equity line.