Methodology

Construction estimators

Material take-offs use standard contractor methods: NRCA roof-pitch multipliers to convert footprint to sloped area, 100-sq-ft 'squares' for roofing and siding, 16-inch on-center joist/stud spacing, and waste allowances of 5–22% by complexity. Concrete is computed by volume (27 cubic feet per cubic yard); bag yields follow manufacturer figures. Cost ranges are directional installed estimates, not quotes.

Sources: NRCA — roofing standards · SMACNA — sheet metal / gutter sizing

Finance & tax tools

Tax tools use the official 2026 federal brackets, standard deductions, FICA/self-employment rates, capital-gains brackets, and the standard mileage rate (IRS Rev. Proc. 2025-32 and Notice 2026-10) — all published on our reference page. Loan, mortgage, and savings tools use standard amortization and monthly compounding. Figures are planning estimates; verify against IRS.gov and consult a CPA for filing.

Sources: IRS — official tax figures · Smart Cost Hub 2026 tax-rate reference

Health & fitness tools

Basal metabolic rate uses the Mifflin-St Jeor equation (the most accurate for most people); total daily energy expenditure multiplies BMR by a standard activity factor (1.2–1.9). BMI uses the WHO weight/height² definition and category ranges. Body fat uses the U.S. Navy circumference method. These are screening estimates, not medical advice.

Sources: Mifflin-St Jeor equation (NIH) · WHO — BMI classification

Math & everyday tools

Percentage, age, tip, and discount tools use exact arithmetic with no rounding beyond display. Date math uses real calendar dates, so leap years and varying month lengths are handled correctly.