Methodology
Every calculator on SacredRadar uses a documented formula. This page shows the math behind each tool, the sources we use, and the assumptions we make.
Calculator Formulas
Mortgage Payment (fixed-rate)
Monthly Payment = Loan × [r(1+r)ⁿ] / [(1+r)ⁿ − 1]
where r = annual rate ÷ 12 and n = loan term in months.
Property Tax
Annual Tax = Assessed Value × Effective Rate
Rates are statewide averages; actual rates vary by county and municipality.
Refinance Savings
Lifetime Savings = (Old Payment − New Payment) × Remaining Months − Closing Costs
PMI (Private Mortgage Insurance)
Monthly PMI = Loan Amount × Annual PMI Rate / 12
Typical annual PMI rate: 0.3%–1.2% depending on credit score and down payment.
Mortgage Interest Deduction
Deductible Interest = Total Annual Interest Paid (for loans up to $750,000 principal)
Applies to primary and secondary residences. Itemizers only.
Affordability (28/36 rule)
Max Monthly Housing = Gross Monthly Income × 0.28
Max Total Debt = Gross Monthly Income × 0.36
Data Sources
- Property Tax Rates — Tax Foundation, Census Bureau American Community Survey (2024)
- Median Home Values — Zillow Home Value Index, Census Bureau (2024)
- Mortgage Rates — Freddie Mac Primary Mortgage Market Survey (PMMS)
- Tax Rules — IRS Publication 936 (Home Mortgage Interest Deduction)
Assumptions and Limitations
These calculators provide estimates for informational and planning purposes. They are not financial, tax, or legal advice. Actual payments, taxes, and deductions depend on your specific situation, lender terms, local regulations, and tax law changes.
- Mortgage calculator assumes a fixed-rate conventional loan.
- Property tax rates are statewide averages; actual rates vary by county.
- PMI estimates are based on typical ranges; actual rates vary by lender and credit profile.
- Tax deduction figures assume the taxpayer itemizes deductions.
- All dollar amounts are rounded to the nearest dollar for readability.