Dates & time
Ages, gaps and deadlines, counted correctly. 3 tools, all free and all running in your browser.
Forms want your age in years; eligibility rules want it on a specific date. Enter a date of birth and the date you are measuring to, and this gives the exact figure rather than a rounded one.
Count the gap between two dates without a calendar and a pencil. It separates calendar days from working days, which is the distinction that matters for notice periods and project deadlines.
Deadlines are usually expressed as a duration — 90 days from signature, 30 working days from filing, six months from today. This turns that into an actual date on the calendar.