Age Calculator
Enter birth date and reference date – instantly get years, months, days and total days
- Updated
Default: today. Another date shows the age on that day.
Age
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–How the age calculator determines your exact age
Calendar-accurate, leap years included
The age calculator calculates the exact age between a birth date and a freely selectable reference date – by default, today's date. The result is given in four formats: years, months, days (calendar-based) as well as the total number of days as an absolute value. The calendar calculation uses a borrow algorithm that accounts precisely for month and year boundaries – even with irregular month lengths such as February.
A frequently underestimated detail in age calculation is the handling of leap years. The year 2024 had 366 days (because of February 29), while 2026 has only 365. This means: someone born on January 1, 2000 was exactly 26 years old on January 1, 2026 – and had lived exactly 9,497 days. Our calculator adds these leap year days automatically.
The reference date can be freely chosen – for example for retirement, anniversaries, or insurance questions. In the insurance sector and for contracts, age is often calculated at the start or end of a contract. In inheritance law, a person's exact age at a specific reference date can be legally relevant. Age is also significant for sports clubs (age categories), schools (school enrollment), and medical studies (age groups).
For the curious: your 10,000th day of life falls on May 19, 2027 for a birthday on January 1, 2000 (10,000 total days). Your 25,000th day of life would be about 68 years and 5 months after your birthday. With our date calculator (shift mode), you can calculate exactly on which date your next big "life-day milestone" falls.
Use cases for the age calculator
When do you need an age calculator?
- Personal milestone
- 10,000th day of life, 10,001st morning, or your next round birthday
- Insurance & law
- Determine age at contract start, inheritance, or retirement
- Sports & age categories
- Calculate reference-date age for youth, senior, or age categories
- Medicine & research
- Exact age for studies, check-ups, or vaccination schedules
- School & daycare
- Reference-date age for school enrollment (September 30) or daycare registration
- Curiosity & trivia
- How many days have you already lived? What is your life-day record?
Calculation examples
- Birth date
- 01/01/2000
- Reference date
- 01/01/2026
- Age
- 26 years
- Total days
- 9,497
- Birth date
- 02/29/2000
- Reference date
- 03/01/2026
- Age
- 26 years, 0 months, 0 days
- Note
- Borrow algorithm: Feb 2026 = 28 days
Frequently asked questions about the age calculator
Calendar calculation, leap years and special cases explained
How does the age calculator determine the exact age?
The calculator uses a calendar-based borrow algorithm: it first calculates the difference in years, months and days separately. If the day difference becomes negative (e.g. birthday on the 31st of the month, current day on the 15th), one month is borrowed and filled with the days of the previous month; if that day does not exist in the previous month (such as the 31st in February), the month ends on its last day (Section 188(3) of the German Civil Code). The same applies to months. The result is always exact, in the notation "X years, Y months, Z days".
How is the age calculated for leap year birthdays (February 29)?
In years without February 29, the year of life ends when February 28 is over (Section 188(3) of the German Civil Code). On February 28 one day is still missing; on March 1 of a non-leap year, a February 29 birthday results in a remaining age of 0 days – the year of life is complete. On March 1, the corresponding age would thus be an exact whole number of years.
What is the difference between total days and years/months/days?
Total days indicate how many days in total have passed since the birth date – simply the difference in milliseconds divided by 86,400,000 (ms per day). This number accounts for all leap years precisely. The display in years/months/days is calendar-based and can differ slightly, since months have varying numbers of days.
Can I calculate the age at a different reference date?
Yes. The "reference date" field is freely selectable. By default, it is set to today's date. For example, you can enter the date of a future birthday to calculate how old you will be then, or a date in the past to determine a historical age. The "Reset reference date to today" button always takes you back to the current day.
How many days do typical stages of life span?
Some reference values: 18 years = approx. 6,574 days (including leap days), the 10,000th day of life ≈ at 27 years 4–5 months, 65 years (retirement age) = approx. 23,741 days, 100 years = approx. 36,525 days. The exact number depends on the leap years within your lifespan. Our age calculator shows the exact total days based on your specific birth date.