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CalcPier
CalcPier

Methodology

Every calculator on CalcPier is built on standard formulas documented by federal agencies and industry sources. We do not invent proprietary calculations, and we never adjust results to favor any lender.

Formulas we use

  • Mortgage PITI — M = P × [r(1+r)n] / [(1+r)n − 1], where P is principal, r is monthly rate, n is number of payments
  • DSCR — Net Operating Income ÷ Annual Debt Service
  • LTV — Loan Amount ÷ Property Value
  • DTI — Monthly Debt Payments ÷ Monthly Gross Income
  • FHA MIP — 1.75% upfront (UFMIP) + 0.55% annual (30-year, 3.5% down)
  • VA Funding Fee — tiers by down payment: 2.15% (first use, <5% down), 3.30% (subsequent, <5% down), 1.50% (≥5% down), 1.25% (≥10% down)
  • Cap Rate — Net Operating Income ÷ Purchase Price
  • Cash-on-Cash Return — Annual Pre-Tax Cash Flow ÷ Total Cash Invested
  • HELOC payment — interest-only during draw period, then amortizing (M = P × [r(1+r)n] / [(1+r)n − 1])
  • Refinance break-even — Total closing costs ÷ Monthly payment savings
  • PMI cancellation — LTV ≤ 80% (borrower request) or ≤ 78% (automatic, Homeowners Protection Act 1998)

Each formula is implemented as a pure function and covered by automated tests. The full source code is verified against the agency documentation linked below.

Data sources

  • Freddie Mac Primary Mortgage Market Survey (PMMS) — accessed daily via the Federal Reserve Economic Data (FRED) API for MORTGAGE30US and MORTGAGE15US
  • HUD — FHA loan limits (updated annually)
  • FHFA — Conforming loan limits (updated annually)
  • US Census Bureau (American Community Survey) — median home values and property tax rates
  • CFPB — mortgage disclosure standards
  • IRS — property tax deduction rules and reporting standards

Rates displayed as "live" or "updated daily" are fetched automatically at site build time and reflect the most recent Freddie Mac PMMS observation.

Update frequency

  • Mortgage rates — daily (automated FRED fetch)
  • Loan limits — annually (when HUD / FHFA publish new values)
  • State market data — quarterly review
  • Editorial content — reviewed monthly

What we don't do

  • We don't accept payment to alter calculations or rankings
  • We don't recommend specific lenders as "best"
  • We don't provide financial, legal, or tax advice
  • We don't sell user data to third-party brokers

Report an error

If you find a calculation or factual error, email [email protected] with the page URL and the specific issue. We investigate and correct within 48 hours when verified.