THE NUMORIX GUIDE
How to use the PMI Calculator
Last reviewed September 14, 2026
What this calculator does
The conventional-PMI estimate calculates loan amount as home value x (1 - down payment percent/100), then LTV as loan amount divided by home value.
Formula and method
The conventional-PMI estimate calculates loan amount as home value x (1 - down payment percent/100), then LTV as loan amount divided by home value. Monthly PMI is either the quoted monthly override or loan amount x annual PMI rate / 100 / 12. The engine also amortizes the loan at the entered interest rate and searches month by month for balances at 80% and 78% of home value.
Variables and inputs
Enter home value, down payment percent, quoted annual PMI rate, optional quoted monthly PMI, interest rate, and loan term in years. Home and loan values are dollars; down payment, PMI rate, and interest rate are percentages; the term is years.
Worked example
For a $400,000 home with 15% down, loan amount is 400,000 x (1 - 0.15) = $340,000 and original LTV is 340,000 / 400,000 x 100 = 85%. At a quoted annual PMI rate of 0.8%, monthly PMI is 340,000 x 0.008 / 12 = $226.67. If a lender quotes $180 monthly instead, entering the override makes $180 replace the annual-rate calculation.
How to interpret the result
The result is a conventional PMI estimate tied to a quoted rate or premium and a modeled amortization schedule. The 80% and 78% months are estimates of balance thresholds, not an automatic cancellation date; lender notices, request rules, property value, and applicable law control.
Common mistakes to avoid
Enter annual PMI rate as 0.8 for 0.8%, not 0.008. Do not enter both a quoted monthly amount and expect the annual rate to be used; any positive override takes precedence. Keep PMI distinct from FHA MIP, VA funding fees, and USDA guarantee charges.
Assumptions and limitations
The route models only a conventional loan with a fixed rate and no extra principal. It does not apply lender-specific PMI cancellation policies, appreciation, automatic termination exceptions, taxes, fees, insurance, risk-based quote tables, or changes in the loan balance beyond regular amortization.