Calculator Basics · Methodology
Calculator Methodology
How we compute mortgage math — formulas, fee schedules, verification scenarios, and source citations for every published calculator.
Calculator math documentation · CalculatorBasics.com · Last updated 2026-08-24
Published methodologies
- Mortgage Calculator
PITI amortization with loan-type fees (conventional PMI, FHA MIP, VA funding fee, USDA guarantee) and optional extra payments.
- Refinance Calculator
Break-even months, term-change lifetime savings, discount points, escrow pass-through, and PMI removal modeling.
- Affordability Calculator
Reverse 28/36 rule: annual income and monthly debts constrain maximum home price via binary search on PITI.
- Tax Calculator
2026 federal marginal brackets (IRS Rev. Proc. 2025-32) with filing-status-specific schedules.
- Verification Matrix — August 2026
Independent 12-scenario verification of mortgage and refinance math against standard amortization and HUD/VA/USDA fee schedules.