How this age in days calculator works
Calculation: floor((today − DOB) / 86,400,000 ms) on UTC midnights, which makes leap years and DST irrelevant. Age in whole years uses calendar months (birthday test), weeks is days ÷ 7. Enter any birth date from 1900–today; the same engine powers countdowns for 'days until 100', '10,000-day milestones' and 'days since' any date if you read the numbers with your own arithmetic.
Frequently asked questions
Are leap years counted correctly?
Yes — the diff uses UTC date-to-date epoch arithmetic, so every Feb 29 included in your span counts as a day lived automatically. The only edge case: born Feb 29, your legal 'next' birthday lands Mar 1 in non-leap years, which this countdown also handles.
How many days in a 100-year life?
≈36,524 days (25 leap days per century; 36,524 is the famous first-century number before the 100-year non-leap rule). Milestones most people hit: 10,000 days (27.4 y), 20,000 (54.8 y), 30,000 (82.2 y).
Does the time of birth matter?
Only within the same calendar day — the tool counts whole 24-hour days from midnight UTC. For precise 'hours alive' it's approximate; for social-media age-in-days use, exactness is the day itself.