A calculator with wrong math is worse than no calculator at all. Here's exactly how each one is built, checked, and verified before it's ever sold.
Every figure is sourced
Rates, thresholds, ratios, and standards are never guessed. Each one is pulled from an authoritative or clearly reliable source — official bodies where possible, or established references that cite them directly. Sources are listed inside every calculator, on their own dedicated sheet, so you can check them yourself.
Every figure is cross-checked
Numbers are verified against a second, independent source before they go into a formula. If two sources disagree, or a figure can't be confirmed, that's flagged directly in the file rather than quietly guessed at.
Every formula is recalculated and tested
Formulas are built with tracked cell references, not hardcoded row numbers. Before a calculator is sold, the whole file is recalculated end-to-end to check for formula errors, and the output is hand-traced against a real example to confirm the math holds up — not just that the spreadsheet opens without errors.
What these calculators are not
They're simplified, practical estimators — not official filing tools or professional advice. Each one states plainly what it assumes and what it leaves out. When the underlying rules or standards change, a new dated version is published rather than silently updated underneath you.
Something looks wrong?
If you find a number that looks off, that's worth knowing about immediately. Get in touch and it'll be checked and corrected.