Last updated: August 2026
Every calculator on this site is written by hand, not wrapped around a third-party widget, and each one is tested before it ships. This page explains the process so you can judge how much weight to put on the numbers.
Where the formulas come from
Each calculator implements a published, citable method rather than an approximation invented for convenience. Some examples of what that means in practice:
- VA disability rating follows the combined ratings method in 38 CFR 4.25, applying each rating in descending order to remaining efficiency with no intermediate rounding, plus the bilateral factor in 38 CFR 4.26.
- Taxable Social Security benefits uses the IRS provisional income test and both threshold tiers as set out in Publication 915.
- eGFR uses the CKD-EPI 2021 equation, the race-free revision.
- Creatinine clearance uses Cockcroft-Gault, reported against actual, ideal and adjusted body weight because drug labelling differs on which to use.
- Freight class uses the full eighteen-bracket NMFC density scale.
- Federal income tax applies the published bracket tables and standard deductions for each tax year, applied bracket by bracket rather than as a flat effective rate.
- Astronomical positions in the birth chart tools use Julian day conversion, solar longitude, a standard lunar series and the ascendant formula from local sidereal time, latitude and the obliquity of the ecliptic.
How they are tested
Two automated test suites run against every build.
The first mounts all calculators in a headless browser and checks that each one renders, produces a result, contains no undefined values, and has no duplicate element identifiers. That last check caught a real bug in the lottery calculator, where a results row shared an identifier with the headline figure and silently overwrote it.
The second compares computed output against values worked out independently. The VA calculator is checked against the published combined ratings table; the solar position tools against the 2024 equinoxes and solstices; the lunar tools against the timing of real new and full moons; the lottery odds against known game formats. Where a check disagrees with the code, the disagreement is investigated rather than the expectation simply adjusted.
What we do not build
Some calculators were deliberately left out because building them accurately was not possible with sources we could verify. Publishing a plausible-looking number in these areas would be worse than publishing nothing:
- Cardiovascular risk scores, because the Pooled Cohort Equations coefficients could not be verified to the necessary precision and the model is being superseded.
- Infant growth percentiles, which require the full WHO reference tables.
- Military fitness test scoring, which requires the official scoring tables.
- Peptide and research-chemical dosing, which we will not build at all.
- Housing allowance rates and toll costs, which depend on proprietary datasets. Where a tool needs one of these, it asks you to supply the official figure instead of guessing it.
What these calculators are not
They are estimates and educational tools. They are not financial, legal, tax or medical advice, and they cannot account for your particular circumstances. Rates, thresholds and tables change, sometimes mid-year. Always confirm anything that matters against the primary source or with a qualified professional before acting on it.
Corrections
If you find a calculator that disagrees with an authoritative source, please tell us through the contact page and include the source. Corrections are made promptly and the last updated date on the affected page is revised.