Calculation Accuracy

How we build calculators

Every calculator on Numbarn follows a consistent accuracy process:

1. Source identification. We identify the authoritative source for the formula — IRS publications for tax, CDC/WHO for health metrics, standard mathematical references for math.
2. Implementation. The formula is implemented and the source is recorded in the calculator metadata.
3. Testing. Each formula is tested against known reference values, boundary conditions, and edge cases using automated tests.
4. Review. The source, formula, worked example, and test results are reviewed before publishing.
5. Ongoing verification. Finance/tax calculators are reviewed when official sources publish updates. Health calculators are reviewed when guidelines change.

What you see on each page

• Formula. The mathematical formula or method used.
• Worked example. A concrete example with real numbers so you can verify the math yourself.
• Sources. Links to the authoritative references used (shown on finance and health pages).
• Disclaimer. Clear statement that results are estimates, not professional advice.

Limitations

All calculators produce estimates based on simplified models. Real-world outcomes depend on factors these tools cannot capture:

• Tax calculators use standard deductions and federal brackets only — state/local taxes, credits, and itemized deductions are not modeled.
• Mortgage calculators estimate principal and interest and can include optional taxes, insurance, PMI, HOA, and maintenance — actual lender quotes still depend on credit, DTI, escrow practices, and market conditions.
• Health calculators use population-level formulas — individual metabolism, genetics, and medical conditions vary significantly.
• Investment projections assume steady returns — real markets are volatile.

Testing infrastructure

Numbarn uses automated formula tests that run on every code change. These tests verify that calculator outputs match known reference values within acceptable tolerances. If a formula change causes unexpected output differences, the test suite catches it before deployment.