How we test our calculators, and what to do if something looks wrong.
Last updated: July 2026
We separate our calculators into two categories, and hold each to a different, clearly-labeled standard:
Calculators like Loan, Mortgage, Retirement, Investment Return, FIRE, Net Worth, Tax, and HSA are based on precise, well-established formulas or current published government figures (like IRS tax brackets). We aim for these to be mathematically exact for the inputs you provide.
Calculators like Term Life Cost, Auto Insurance, Home Insurance, and the ACA Subsidy estimator involve real-world pricing that varies by underwriting, location, and insurer — no formula alone can replace an actual quote. These calculators are clearly labeled as estimates, built from published national averages, and always paired with a link to get a real quote.
Before publishing, we manually verify each calculator's output against independently calculated reference examples for representative inputs, checking that the formula is implemented correctly.
Formulas are sourced from standard financial mathematics (amortization, compound interest) or directly from government publications (IRS Revenue Procedures for tax brackets and HSA limits, HHS guidelines for federal poverty levels). Where we've had to approximate a published table (as noted on the ACA Subsidy Estimator page), this is explicitly disclosed on that calculator's page.
IRS.gov, HealthCare.gov, HHS.gov, and other primary government sources for law- and figure-dependent calculators; published industry-average data for cost-estimate calculators.
If you spot something that looks wrong, please tell us — use our Contact page or the Help Center's bug report option. We review every report and correct genuine errors promptly.