Date and time calculators: age, duration, business days and more

Date arithmetic is the kind of thing you should be able to do in your head, and mostly you can. The cases where mental arithmetic fails are the ones that matter — contracts, payroll, visas — so these are exact.

All the calculators tools

The full set runs on the home page, where they share one live clock and stay in step with each other.

Reading on calculators

• Why Are There 60 Seconds in a Minute? Blame Ancient Babylon
• How Many Seconds Are in a Day, a Week, and a Year? The Full Count
• Business Days vs Calendar Days: Why ‘5 Days’ Can Mean
• Unix Time: The Invisible Number Behind Every Computer Clock
• The Pomodoro Technique: Working in 25-Minute Slices
• From Milliseconds to Attoseconds: The Small Units of Time
• Time Capsules: Messages Scheduled Centuries Ahead