About Percentage Guru
Percentage Guru exists because reverse percentages are the one piece of everyday arithmetic almost everyone gets wrong in the same way — by adding the percentage back instead of dividing it out. Every calculator here does that division correctly and shows its working.
Who builds this
Percentage Guru is designed, built and maintained by Pushkar Kumar, a front-end developer (GitHub). No figure on this site rests on anyone's word, the author's included: every formula is enforced by the automated test suite described under corrections below, and errors, once reported, are fixed in the open.
What makes these calculators different
Every answer shows its check. The tool re-applies the percentage forwards and prints the result, so you can verify it without trusting us. Where rounding means the displayed figure will not reconcile to the penny, it prints ≈ rather than = instead of quietly hiding the difference.
The awkward cases are explained, not fudged. A 100% discount has no recoverable original, and plenty of calculators will happily print ∞ or an error code. This one explains why the answer does not exist.
It is fast because it is nearly nothing. Static HTML, system fonts, one small script, no ad networks, no trackers. Pages finish loading before most competitors have fetched their first banner.
Nothing you type leaves your device. Every calculation runs in your browser. There is no server to send it to.
How it is paid for
Some pages carry affiliate links to accounting software, clearly labelled, and there may be modest display advertising later. Neither will ever sit inside a calculator or between a heading and its tool. Full detail is on the disclaimer page.
Corrections
The maths is covered by an automated test suite, including the edge cases most calculators get wrong. If you find an error in a figure, a rate or an explanation, please tell us — see contact.