How to Calculate Age from a Date of Birth
Hesaplayıcı3 min read
Short answer
Age is the current year minus the year of birth, less 1 if this year's birthday has not come yet. For months and days, count full months first, then the remaining days. For example, someone born on 15 May 1990 is 36 years, 3 months and 29 days old on 13 September 2026, after 13,270 days.
Formula
age = difference of the years − (1 if the birthday has not come yet)
total days = date − birth date
full weeks = ⌊total days / 7⌋
days left = next birthday − date
- difference of the years: the year of the date minus the year of birth
- date: the day the age is calculated for; when empty, today in Türkiye time
- total days: the calendar days between the two dates. The day you were born counts; the day of the calculation does not.
⌊ ⌋: rounding down
For the months and days, full months come off first, then the remaining days are counted. A month is complete when its day is at least the start day. Leap years count as 366 days.
Step-by-step example
The age on 13 September 2026 of someone born on 15 May 1990:
- Difference of the years: 2026 − 1990 = 36. The birthday (15 May) has passed this year, so nothing comes off: the age is 36.
- Months and days: 3 full months and 29 days have passed since 15 May 2026. The age is 36 years, 3 months and 29 days.
- Total days: 2026-09-13 − 1990-05-15 = 13,270 days.
- Full weeks: ⌊13,270 / 7⌋ = 1,895 weeks.
- Days to the next birthday: 2027-05-15 − 2026-09-13 = 244 days.
When the birthday has not come yet
Someone born on 20 September 1990 is 7 days from their birthday on 13 September 2026. Their age is (2026 − 1990) − 1 = 35, or exactly 35 years, 11 months and 24 days. Taking the difference of the years as the age is the most common mistake: before the birthday it gives one year too many.
Age of people born on 29 February
A common year has no 29 February. In common Turkish practice the birthday in those years is 1 March; no law settles this. Someone born on 29 February 2000:
| Date | Age | Days to the birthday |
|---|---|---|
| 2027-02-28 | 26 years, 11 months, 30 days | 1 |
| 2027-03-01 | 27 years, 0 months, 1 day | 0 |
A calculation that takes 28 February as the birthday finds one more year on 28 February. For official purposes, the rule of the institution applies.
Which day is “today”?
Age is counted in calendar days; the time of birth is not used. If you leave the date empty, today is taken in Türkiye time (UTC+3). Close to midnight the date can differ in another time zone; in that case, enter the date yourself.
Worked example: Age on 13 September 2026 of someone born on 15 May 1990
Age
36 years
- Months after the full years
- 3 months
- Days after the full months
- 29 days
- Total days lived
- 13,270 days
- Full weeks lived
- 1,895 weeks
- Days to the next birthday
- 244 days
Step by step
Age
age = difference of the years − (1 if the birthday has not come yet)
age = (2026 − 1990) − 0 = 36 years
Total days lived
total days = date − birth date
total days = 2026-09-13 − 1990-05-15 = 13,270 days
Full weeks lived
full weeks = ⌊total days / 7⌋
full weeks = ⌊13,270 / 7⌋ = 1,895 weeks
Days to the next birthday
days left = next birthday − date
days left = 2027-05-15 − 2026-09-13 = 244 days