Everyday calculations, clearly explained
Compare percentage changes, convert miles and kilometers, and count calendar days. Free tools with formulas and worked examples.
Percentage change →
Compare an original value with a new one and understand the sign of the result.
Miles ↔ kilometers →
Convert international miles and kilometers in either direction.
Days between dates →
Count calendar days without daylight-saving time changing the answer.
Useful answers, with the method beside them
Choose a tool, enter your values, and see the result on the same page. Each calculator explains its formula, gives examples and highlights limits such as a zero starting value or invalid dates.
Your inputs stay in your browser
The tools calculate locally and do not submit your numbers or dates to our server. No account is needed. Read our privacy policy for information about website delivery and security.
Check the assumptions
These are general-purpose arithmetic tools. Calendar days are not business days or inclusive counts; distance uses the international mile. Review the explanation before using a result for an important decision.