Example
Someone born on Sunday, June 17, 1990 is, on October 29, 2026:
- 36 whole years (to June 17, 2026),
- plus 4 whole months (to October 17),
- plus 12 days: 36 years, 4 months, 12 days, or 13,283 days in all.
Their 37th birthday is Thursday, June 17, 2027, 231 days away.
Age milestones
Dates worth marking, for the date of birth entered above. 1 billion seconds comes about 31 years 8 months after birth.
| Milestone | Date | When |
|---|---|---|
| 1,000 days old | — | — |
| 5,000 days old | — | — |
| 1,000 weeks old | — | — |
| 10,000 days old | — | — |
| 1 billion seconds old | — | — |
| 2,000 weeks old | — | — |
| 500 months old | — | — |
| 20,000 days old | — | — |
| 3,000 weeks old | — | — |
| 25,000 days old | — | — |
| 30,000 days old | — | — |
| 1,000 months old | — | — |
Month ends and leap-day birthdays
Age goes up on the birthday, and months are counted on the calendar. If a month is too short for the birth date, such as the 31st, its last day is used.
For someone born on February 29, this calculator treats February 28 as the birthday in other years. Some laws use March 1 instead for things like reaching legal age, so check if it matters.
Frequently asked questions
How old am I if I was born in 1990?
Subtract 1990 from this year, then take 1 off if your birthday hasn’t come yet. In 2026 you’re 36 after your birthday and 35 before it.
How do I calculate age in Excel or Google Sheets?
With the date of birth in A1, =DATEDIF(A1,TODAY(),"y") gives whole years. Use "ym" for the extra months and "md" for the extra days.
What is Korean age?
A traditional East Asian count where a baby is 1 at birth and everyone adds a year on New Year’s Day, so it runs 1 or 2 years ahead of international age. South Korea switched to international age for official use in June 2023.