Most of the time we give age in years. But the same date of birth can be a single total, how many days, weeks, or months you've been alive. That's handy for milestone counts, for a baby's age in weeks, or any time years is too coarse a number.

Your age in days is the number of whole days from your date of birth to today, counted on the real calendar. Leap years and month lengths are all included, with no rounding. Someone born on 1 January 2000, for instance, had lived 9,132 days by the start of 2025.

Your age in weeks is your age in days split into whole weeks, with the leftover days shown separately, say 1,304 weeks and 4 days. Weeks are how parents usually track a baby's age in the first few months.

Your age in months counts the whole calendar months from your birth date to today, plus the remaining days. Because months vary in length, it's counted month by month from your birth date rather than by dividing the day count, the same way you'd count a monthly anniversary.

Want the precise version that's used in clinics and schools? That's your chronological age. To compare two people instead, see the age difference between two dates.