Age Gap Calculator: Age Difference in Years

Age Gap Calculator Compare

Person 1 Name (optional)

Person 1 Date of Birth

Please enter a valid date between 1900 and today.

Person 2 Name (optional)

Person 2 Date of Birth

Please enter a valid date between 1900 and today.

Years

Months

Days

Related Age Tools

How Do You Calculate the Age Gap Between Two People?

Subtract the older person's date of birth from the younger person's, counting whole years, then months, then days. Someone born 15 January 1990 and someone born 3 June 1994 are 4 years, 4 months and 19 days apart. Enter both birth dates above for the exact gap. Subtracting birth years alone can be off by almost a year.

How to Use the Age Gap Calculator

Optionally type both names so the result reads naturally.
Enter each person's date of birth with the calendar picker or by typing it.
Read the gap in years, months and days, who is older, and how old the older person was when the younger was born.

Worked Example: Siblings

Sibling A was born 10 March 2012 and Sibling B on 22 September 2016. Subtracting years gives "4", but the real gap is 4 years, 6 months and 12 days. The months matter for school-year planning. More on this in how to calculate a sibling age gap.

Why Year Subtraction Gets It Wrong

Birth years alone ignore the month and day. Someone born in December 2015 and someone born in January 2018 look "3 years apart" by year, but the actual gap is only 2 years and 1 month. The calculator counts full calendar dates, including leap years, so the answer is exact.

Age Gaps in Relationships: The "Half Your Age Plus Seven" Rule

A popular rule of thumb says the youngest partner you "should" date is half your age plus seven, and the oldest is double your age minus seven (×2 − 14). It appears in a 1901 book by the writer Max O'Rell and has no scientific basis. It's shown here only because people search for it.

Your age	Rule's youngest	Rule's oldest
30	22	46
35	24.5	56
40	27	66
45	29.5	76
50	32	86
60	37	106

What matters in a relationship is consent, the law, shared values and life stage, which no formula measures. Read the history of the rule in where "half your age plus seven" comes from.

Other Reasons to Check an Age Difference

Family planning: the spacing between children.
Eligibility: age gaps set in rules, such as some adoption or sponsorship requirements.
Curiosity: how much older a parent, grandparent or celebrity is than you.

Need one person's age on a particular date instead? Use how old will I be on a date, or the main age calculator.

How the Age Gap Calculator Works

The calculator compares two dates of birth, works out which is earlier, and counts the difference in complete years, then months, then days, borrowing days from the previous month where needed, the same way an exact age is counted, so month lengths and leap years never throw the answer off.

Who Uses the Age Gap Calculator?

Siblings and twins: find the exact gap between brothers and sisters.
Couples: see the age difference precisely, not just in years.
Family history: compare the ages of relatives on a family tree.

How the Age Gap Calculator Saves You Time

Subtracting two dates by hand with month lengths and leap years is slow and error-prone. Enter both dates and the exact gap appears.

Frequently Asked Questions

How do I calculate the age difference between two people?

Subtract the earlier date of birth from the later one: count the full years first, then the extra months, then the remaining days. The calculator does this with real calendar dates, so leap years and different month lengths are handled exactly, and it tells you who is older.

Why is my result different from subtracting birth years?

Year subtraction ignores months and days. People born in December 2015 and January 2018 look three years apart, but the true gap is 2 years and 1 month. Using full dates of birth gives the exact difference, which can be almost a year different from the year-only answer.

What is the half your age plus seven rule?

It is an informal dating rule that the youngest acceptable partner is half your age plus seven, and the oldest is double your age minus seven. At 40 that gives 27 to 66. It appears in a 1901 book by Max O'Rell and is a rule of thumb with no research behind it.

What is a close sibling age gap?

There is no official definition, but siblings less than two years apart are commonly described as close in age, two to four years as moderate, and more than four years as wide. The exact gap in months matters most for school years and childcare planning.

Does the age gap change over time?

No. The gap between two dates of birth is fixed for life. What changes is how the gap feels: five years is a big difference between a 10-year-old and a 15-year-old, but much less noticeable between 45 and 50. The calculator also shows how old the older person was when the younger was born.

Can I calculate an age gap if I only know birth years?

Only roughly. Subtracting birth years gives an estimate that can be off by up to a year either way. If you know the months, enter the first of each month as the day to get much closer. For an exact answer you need both full dates of birth.

Last updated: September 2026

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