Report a calculation error
A number on this site that doesn't match the stated formula. Include the page, the values you entered, and the result you expected.
Contact Us
One inbox, no ticket system. Bug reports and translation corrections get priority, since they usually take one calculation to verify.
What to Write In About
Flag a translation issue
A phrase that reads awkwardly, a mistranslated term, or a formula that doesn't match how it's taught in your language.
Request a tool or feature
A calculator this site doesn't have yet, or a feature the current calculator is missing.
Ask a general question
Anything about how a section works, how a number was derived, or how to cite this site.
What to Include
For a calculation error: the page URL, the values you entered, and the result you got versus the result you expected. For a translation issue: the page, the language, and the phrase in question. That's usually enough to reproduce and fix an issue without back-and-forth.
This is a small, independent site rather than a company with a support desk, so replies are best-effort rather than guaranteed on a fixed timeline, but bug reports with a clear repro step are read and, where the math is genuinely wrong, fixed.