How old am I today, exactly? How many days until the wedding? How long did the employment contract run? The Age Calculator (Age & Days) answers all of this with true calendar arithmetic – this tutorial shows what's behind it.
Step by step
- Enter the start date: date of birth or any other date (contract start, first date …)
- Set the reference date (optional): leave empty for today – or date it into the future: how old will I be at retirement?
- Read the result: exact age, total days, weeks, months, hours, weekday of birth and countdown to the next anniversary
Why calculating months is tricky
Months are 28 to 31 days long, and leap years insert a day every four years. Approximations like '30.44 days per month' therefore regularly produce deviations of several days. The calculator instead counts true to the calendar: from 15 March 1990 to 23 July 2026 it is exactly 36 years, 4 months and 8 days – or 13,279 days, 1,897 weeks, around 318,700 hours. Incidentally, 15 March 1990 was a Thursday.
Practical use cases
Far more than birthdays: deadlines (14-day withdrawal, warranty, probation), length of employment for references, vaccination intervals, a baby's age in weeks for the paediatrician, or the relationship duration in days for the anniversary. Also useful backwards: which date lies 90 days before the deadline?
Edge cases solved cleanly
The countdown to the next birthday accounts for leap years; anyone born on 29 February celebrates on 1 March in common years, arithmetically speaking. And when counting total days, the usual convention applies: start and end date at midnight, counting the full days in between – the same logic courts and HR departments use for deadlines.
