Why Age Calculation Is Tricky
Subtracting birth year from the current year gives an approximation. For the exact age — down to months and days — you must account for leap years, variable month lengths, and whether your birthday has passed yet this year.
The Algorithm
Total days = (Today − DOB) ÷ 86400000 ms/day
Years: Count full calendar years from DOB to today
Months: Remaining months after the last full birthday
Days: Remaining days after the last full month
Leap Year Rule
A year is a leap year if: (year % 4 === 0) AND (year % 100 !== 0 OR year % 400 === 0). This gives 366 days instead of 365, which matters for people born on Feb 29.
Worked Example
- DOB: March 15, 1990 | Today: May 5, 2026
- Full years = 36 (birthday March 15, 2026 has passed)
- Remaining months = 1 (April 15 → May 5 is 20 days, not a full month)
- Remaining days = 20
- Total days lived ≈ 13,200 days
Fun Facts About Your Age
- At 1 billion seconds old you are approximately 31.7 years old.
- The average human heart beats ~100,000 times per day — by age 36 that's ~1.3 billion beats.
- You've been alive for roughly 10,000+ sunrises by your 30s.
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