Formulas & sources

Every CalcYard calculator implements a standard, published formula. This page lists the primary references by category. Formulas verified July 2026.

Loans & mortgages

Payments use the standard amortization formula (the same PMT calculation used by lenders and spreadsheets): monthly rate applied to declining balance over the term. FHA MIP, VA funding fees, and USDA guarantee fees use the current published HUD/VA/USDA rate schedules.

Taxes

2025 U.S. federal brackets, standard deduction ($15,000 single / $30,000 married filing jointly), long-term capital-gains thresholds, and the $176,100 Social Security wage base per IRS Rev. Proc. 2024-40. Self-employment tax follows IRS Schedule SE (15.3% on 92.35% of net earnings). Residential rental depreciation uses the 27.5-year straight-line convention.

Health & fitness

BMR: Mifflin-St Jeor equation (1990). Body fat: U.S. Navy circumference method. Ideal weight: Devine formula. Body surface area: Du Bois. One-rep max: Epley. Target heart rate: Karvonen. Pregnancy dating: Naegele’s rule.

HVAC & construction

Ventilation: ASHRAE 62.2 (0.03 × floor area + 7.5 × (bedrooms + 1)). Airflow: sensible-heat formula (CFM = BTU/hr ÷ 1.08 × ΔT). Load estimates are simplified Manual-J-style figures — final equipment sizing requires a full Manual J. Material formulas use standard industry coverage rates and include stated waste factors.

Weather

Wind chill: NWS 2001 formula. Heat index: NWS Rothfusz regression. Dew point: Magnus approximation.

Finance & statistics

Compound growth, present/future value, IRR (bisection on NPV), CAGR, and the Rule of 72 use their textbook definitions. Statistics tools use standard sample/population formulas; confidence intervals use z-scores.

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