# What is our age difference?

Works out the gap between two birth dates in years, months, and days, the total days, and who is older.

- Page: https://www.acalculator.org/days/age-difference-calculator
- JSON spec: https://www.acalculator.org/days/age-difference-calculator.json
- Version: 5cadf9d72509

## Default answer

Example with the default inputs (First person’s birth date October 5, 2026, Second person’s birth date October 5, 2026) on the example date Monday, October 5, 2026: Person 1 and Person 2 are the same age; the age gap is 0 days.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| name1 | First person’s name | A name for the first person, used in the answer. |
| birth1 | First person’s birth date | The first person’s date of birth. |
| name2 | Second person’s name | A name for the second person, used in the answer. |
| birth2 | Second person’s birth date | The second person’s date of birth. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| difference | Age difference | Whole years, then whole months, then days from the earlier birth date to the later one. |
| older | Who is older | Which person was born first. |
| days | Total days | Days between the two birth dates. |
| weeks | Total weeks | The total days as whole weeks and days. |
| months | Total months | Completed months between the two birth dates. |

## Method

From the earlier birth date, count whole years while the later birth date is not passed, then whole months, then the days left.

## Assumptions

- A month is counted when the same day of the month is reached; when that month is shorter, its last day counts (January 31 plus one month is February 28, or 29 in a leap year).
- A year from February 29 ends on February 28 in a common year.
- The difference is the same whichever person is entered first.
- Dates are calendar days with no time of day or time zone.

## Worked examples

1. birth1 = 1990-05-15, birth2 = 1995-08-20 gives difference = {"years":5,"months":3,"days":5}, older = Person 1 is older than Person 2, days = 1,923, months = 63. Source: U.S. Naval Observatory, Leap Years: the Gregorian leap year rule. https://aa.usno.navy.mil/faq/leap_years.
2. name1 = Ann, birth1 = 2010-06-01, name2 = Bob, birth2 = 1970-06-01 gives difference = {"years":40,"months":0,"days":0}, older = Bob is older than Ann, days = 14,610, weeks = {"weeks":2087,"days":1}. Source: U.S. Naval Observatory, Leap Years: the Gregorian leap year rule. https://aa.usno.navy.mil/faq/leap_years.
3. birth1 = 2024-02-29, birth2 = 2025-03-01 gives difference = {"years":1,"months":0,"days":1}, days = 366. Source: U.S. Naval Observatory, Leap Years: the Gregorian leap year rule. https://aa.usno.navy.mil/faq/leap_years.
4. birth1 = 1999-12-31, birth2 = 1999-12-31 gives difference = {"years":0,"months":0,"days":0}, older = Person 1 and Person 2 are the same age, days = 0. Source: U.S. Naval Observatory, Leap Years: the Gregorian leap year rule. https://aa.usno.navy.mil/faq/leap_years.

## FAQ

### How does the Age Difference Calculator work?

The Age Difference Calculator calculates the precise difference between two birth dates in years, months, and days. It determines which person is older and shows the exact time difference between their birth dates.

### Can I calculate age difference between any two dates?

Yes, you can calculate the age difference between any two birth dates. The calculator works with dates from the past, present, and even future dates for planning purposes.

### What if both people have the same birth date?

If both people have the same birth date, the calculator will show that they are the same age with no difference in years, months, or days.

### How accurate is the age difference calculation?

The calculation is very accurate, taking into account leap years, varying month lengths, and precise day counting. It provides the exact difference in years, months, and days between two birth dates.

### Can I use this calculator for planning events?

Yes, this calculator is perfect for planning events where age differences matter, such as birthday parties, family gatherings, or understanding generational gaps between family members.

### What information do I need to use the calculator?

You need the birth dates of both people. You can also optionally add names for each person to personalize the results. The calculator will automatically determine which person is older.

### How is the age difference displayed?

The age difference is displayed in a clear format showing years, months, and days. For example: '2 years, 3 months, 5 days'. The calculator also shows which person is older, the total days, weeks, and months between the birth dates.

### Can I calculate age differences for historical figures?

Yes, you can use this calculator to compare birth dates of historical figures, celebrities, family members, or anyone whose birth date you know. Dates follow the Gregorian calendar, so for births recorded in the Julian calendar (before 1582 in most of Europe, later elsewhere) convert the dates first.

### Is this calculator free to use?

Yes, the Age Difference Calculator is completely free to use. You can calculate as many age differences as you need without any cost or registration required.

### What are some practical uses for this calculator?

This calculator is useful for understanding family relationships, planning age-appropriate activities, comparing life milestones, genealogical research, and general curiosity about age differences between people.

## Sources

- U.S. Naval Observatory, Leap Years: the Gregorian leap year rule. https://aa.usno.navy.mil/faq/leap_years