References & Data Sources
Transparency matters. This page documents the formulas, assumptions, and external references used across the calculators and guides.
How We Use These Sources
We prefer government and GSE sources for core mortgage concepts, then use supplemental market references for context. This page was last reviewed on 2026-03-06.
Calculation Formulas
Monthly Mortgage Payment Formula
M = monthly payment, P = principal, r = monthly interest rate, n = number of scheduled payments.
PMI (Private Mortgage Insurance) Estimate
PMI is commonly required when the down payment is below 20 percent. The actual rate depends on loan structure and borrower profile.
Loan-to-Value (LTV) Ratio
LTV helps determine loan eligibility, PMI assumptions, and refinance thresholds.
Debt-to-Income (DTI) Ratio
DTI compares monthly debt obligations against gross income and is commonly used in underwriting.
Source Library
Government Agencies
Regulates the housing GSEs and publishes market data.
Consumer guidance for mortgages, disclosures, and lending practices.
Housing guidance and federal housing program information.
Official FHA-related borrower guidance through HUD.
Official VA home loan program information.
Rural housing loan and grant program information.
Government-Sponsored Enterprises
Mortgage market guidance, learning resources, and underwriting references.
Mortgage education, surveys, and loan program information.
Supplemental Market References
Weekly mortgage rate averages used for market context.
Industry research and mortgage market commentary.
Housing market data and consumer market context.
Methodology & Assumptions
Amortization Schedule Calculation
Schedules use a standard declining-balance method. Each scheduled payment first covers accrued interest, and the remainder reduces principal.
Property Tax Estimates
Default tax estimates are illustrative. Actual property taxes vary materially by state, county, municipality, exemptions, and reassessment policy.
Homeowners Insurance Estimates
Insurance estimates use broad national assumptions and should be replaced with insurer quotes whenever possible.
PMI Rate Assumptions
PMI assumptions are scenario-based estimates. Actual borrower pricing varies by down payment, credit, occupancy, and loan program.
Important Limitations
MortgageCalcMaster provides planning estimates, not lender offers or legal advice. Actual outcomes can vary because of lender pricing, borrower profile, property-specific costs, local regulation, and timing.
Review our full disclaimer before making financial decisions.
Page Information
Last reviewed: 2026-03-06
Reviewed by: MortgageCalcMaster Editorial Team