Pick your date of birth and the calculator gives your exact age in years, months and days, counted the way calendars and laws count anniversaries. It also shows the weekday you were born on, how many months, weeks, days and hours you have lived, and how long until your next birthday. Today’s date is your own day, wherever you are.
How ages are counted
Whole months come first, then the days left over:
- From May 15, 1990 to November 6, 2026: 36 years and 5 months take you to October 15, 2026, and 22 more days to November 6. The age is 36 years, 5 months, 22 days.
- When a month is shorter than the starting day, the anniversary falls on its last day: one month after January 31 is February 28 (or 29 in a leap year).
- A person born on February 29 has their birthday on February 28 in common years.
Fun milestones
| Milestone | Age |
|---|---|
| 1,000 weeks | 19.2 years |
| 10,000 days | 27.4 years |
| 1 billion seconds | 31.7 years |
| 500 months | 41.7 years |
| 20,000 days | 54.8 years |
Your 10,000th day is a quiet birthday most people miss: about 27 years and 4.5 months after you were born. The calculator shows your days lived, so you can see when yours comes.
Age in different systems
In most of the world, you turn one year older on your birthday. A few traditions count differently: in the traditional East Asian system, a baby is one year old at birth and everyone gains a year at the New Year. South Korea, the last country to use it widely in daily life, switched its official documents to international age in June 2023. This calculator always gives the international age.
Uses beyond birthdays
- Age on a given date: eligibility for school, sports categories, pensions or travel discounts often depends on your age on a fixed day. Set the second date to that day.
- Length of a relationship or a job: enter the start date as the “date of birth”.
- Ages of documents and buildings: the same counting works for anything with a start date.
Dates are worked out on your device in your own calendar day, so the answer is right whether you are in Tokyo or Toronto. Once zet4u is saved on your device, it works offline as well.
Frequently asked questions
How is exact age calculated?
Whole months are counted first, from your birthday to the same day of a later month, then the days left over. Someone born on May 15, 1990 is 36 years, 5 months and 22 days old on November 6, 2026.
When does someone born on February 29 have a birthday?
In years without a February 29, the calculator counts the birthday on February 28, which is how most legal systems treat it for ages and deadlines.
How many days old am I?
The calculator counts every day between your birth date and today, leap days included. 10,000 days is about 27 years and 4.5 months.
Can I see my age on a past or future date?
Yes: change the second date. It is useful for forms that ask your age on a specific day, such as the start of a school year or a competition.
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