Age in Days Calculator
Enter a birth date and an optional reference date to see the total days elapsed, plus equivalent weeks, months, and years.
Leave as-is to use the current date/time.
How to Use This Calculator
Enter start date/time
Use a birth, launch, or event date down to the minute for maximum accuracy.
Set reference date/time
Choose “now” for current age or pick any past/future date to compare.
Review conversions
See days plus equivalent weeks, months, and years for easy reporting or celebration planning.
Formula
Days = (Reference − Birth) ÷ 86,400,000
Weeks = Days ÷ 7
Months (approx) = Days ÷ 30.4375
Years (approx) = Days ÷ 365.25
Example: 1990-01-01 → 2025-11-09 = 13,145.47 days → 1,878.0 weeks (approx).
Why Track Age in Days?
- Celebrate numeric milestones like 5,000 or 10,000 days.
- Translate medical or scientific protocols into days.
- Monitor product lifecycle durations exactly.
- Teach kids math with real-world date comparisons.
Frequently Asked Questions
Does the calculator consider leap years?
Yes—calculations use the exact calendar difference, so leap days are included automatically.
Can I ignore the time of day?
Enter times at midnight (00:00) to treat dates as whole days.
What if I only know the birth date?
Leave the reference field as-is; it defaults to the current moment.
Can I use this for countdowns?
Yes—enter a future event in the reference field to see days remaining.