Rechnerpilot Calculator

Age Calculator

Calculate age in years, months and days, age at a reference date, next birthday, day of the week of birth and days until birthday.

Available

Inputs

Enter values

Live

Enter date

Date of birth and optional reference date. Without reference date, today is used.

Date of birthi

The date of birth as a calendar day.

Reference datei

Optional. Without a reference date, the calculator uses today's UTC date.

Load example

Explanation

How Age Calculator works

The age calculator works with pure calendar dates. Times are not considered, so that daylight saving time and time zones do not affect the result.

Age in years, months and days is calculated as a calendar difference: completed years first, then full months since the last birthday, and finally the remaining days. The current, incomplete year of life is not counted as another full year.

Calendar ageAge = Reference date - Date of birth

The difference is not calculated as a fixed number of 365-day years, but with real calendar years and month lengths.

Knowledge

Why Calendar Age Is Not Just Counting Days

Age is understood in everyday life as full years, months and days. That is why the calculator uses real calendar dates.

Months have different numbers of days and leap years add February 29. Therefore the calculator does not simply subtract 365 days per year.

Full years are counted up to the last birthday.
Then full calendar months follow.
The remaining calendar days form the day remainder.

Practice

Practical examples

For illustration only – your own calculation is what counts.

Age on a fixed reference date

A person born on April 19, 1992 wants to determine their calendar age on July 29, 2026.

Result: On July 29, 2026, the age is 34 years, 3 months and 10 days. The next birthday is April 19, 2027.

Age at Reference Date

A person born on 31 December 1990 is to be classified as of the reference date 1 January 2026.

Result: On January 1, 2026, the age is 35 years, 0 months and 1 day.

Birthday on February 29

For a birthday on February 29, the calculator treats non-leap years as March 1.

Result: On February 28, 2023, the age is 22 years, 11 months and 27 days. The calculator sets the next birthday to March 1, 2023.

Notes

Common mistakes

Time zone affects the result
Users assume that the local time zone changes the calendar age and get different results depending on the time of day.
The age calculator works with pure calendar dates in UTC. The time of day and local time zone play no role as long as a whole calendar day is the unit.
Leap year birthday misinterpreted
People born on February 29 believe they only have a birthday every four years, or that the calculator shows one day too few in non-leap years.
The calculator transparently uses March 1 as its calendar substitute in non-leap years. Legal age limits must be assessed separately under the applicable rules.
Start and end day counted twice
The birthday and the reference date are both counted as full days, leading to a one-day discrepancy.
The calculator counts from the birthday (time point 0). On the first birthday after that, exactly one year has passed. The reference date itself marks the achieved age.
One year always calculated as 365 days
Some calculate age by dividing the days since birth by 365. This leads to rounding errors for older persons.
The calculator uses real calendar years with 365 or 366 days. This ensures the result matches the calendar age to the exact day.

FAQ

Frequently asked questions

What date does the age calculator use without a reference date?

If no reference date is entered, the calculator uses today's date from the browser's UTC time.

How is the age in years, months and days calculated?

The calculator first counts full years, then full calendar months and finally the remaining days up to the reference date.

How does the calculator handle February 29?

In leap years, the birthday remains February 29. In non-leap years, the calculator sets the next birthday to March 1.

Why does the calculator use UTC?

Calendar dates are compared without time. UTC prevents daylight saving changes or local time zones from shifting the day result.

Can I enter a date of birth in the future?

No. A date of birth after the reference date is not a valid age and is displayed as an error.

What is the difference between completed years and the current year of life?

Completed years are the years that have fully elapsed and match the year count in the result. Someone who has completed 35 years is in their 36th year of life; that incomplete year is not shown as age 36.

How accurate is the age calculation for newborns?

The calculator counts from the date of birth in whole calendar days. For newborns it shows the age in days, weeks and months. The exact time of birth is not considered, so on the birthday itself a difference of up to one day can occur.

Can I use the calculator for age calculations in insurance law?

The calculator provides a calendar-based model calculation. Legal age limits may depend on sections 187(2) and 188 of the German Civil Code and on special rules. The calculator does not make a legally binding determination.

Limits

Limitations

The calculator only works with calendar dates. Times and exact birth times are not considered.
The calculator does not determine legal age limits. Sections 187 and 188 of the German Civil Code and special rules may be relevant.
The calculation uses UTC dates. In rare cases, the local calendar day may differ from the UTC date (e.g., shortly after midnight in time zones far west of Greenwich).
For dates before the introduction of the Gregorian calendar (1582), the calculation is purely mathematical and not historically exact.

Sources

Sources and references

ISO 8601 – Darstellung von Datum und UhrzeitInternationale Organisation für Normung (ISO)
International standard for the unambiguous representation of Gregorian calendar dates, including the YYYY-MM-DD format read by the calculator.
View sourceRetrieved: 07/29/2026 · Verified on: 07/29/2026
Paragraph 188 BGB – FristendeBundesministerium der Justiz
Governs the end of periods defined in weeks, months or years and the case where the relevant calendar day is absent from the final month.
View sourceRetrieved: 07/29/2026 · Verified on: 07/29/2026 · Primary source
Paragraph 187 BGB – FristbeginnBundesministerium der Justiz
Section 187(2) states that the day of birth is included when calculating a person's age.
View sourceRetrieved: 07/29/2026 · Verified on: 07/29/2026 · Primary source
Gregorianischer Kalender – SchaltjahrregelungPhysikalisch-Technische Bundesanstalt (PTB)
Explanation of the Gregorian calendar with leap year rule: A year is a leap year if divisible by 4, unless divisible by 100, unless divisible by 400.
View sourceRetrieved: 09/09/2026 · Verified on: 07/29/2026

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