Age Difference Calculator (Between Two Birthdays)
Find the exact age difference between two people from their dates of birth: who is older and by how many years, months and days, or the gap in total days, weeks, months or decimal years.
Last updated: October 2026
Age difference
Person A is older by 4 years, 7 months, 19 days
Formula below · 3 sources (developer.mozilla.org, aa.usno.navy.mil, bilinguistics.com) · Updated Oct 2026
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About this calculator
The age difference between two people is the time between their dates of birth, and it never changes: the gap on the day the younger one was born is the gap for life. Because birthdays are calendar dates, the natural way to state it is in years, months and days.
How it is counted
Starting from the older person's birthday, count the whole years that fit before the younger person's birth date, then the whole months, then the days left over, using the real length of each month. Person A born March 14, 1988 and Person B born November 2, 1992: four years later is March 14, 1992; seven more months is October 14, 1992; from there to November 2 is 19 days. Person A is older by 4 years, 7 months, 19 days.
When the older person's birth day does not exist in a later month (born on the 31st), that month is counted as complete on its last day, the same convention banks and courts use for monthly terms.
Other formats
Total days is the exact number of days between the two dates (1,694 in the example). Weeks divides that by 7 (242 weeks), decimal years by 365.2425, the mean Gregorian year (4.64 years). Total months adds the fraction of the partial month to the whole months (55.61).
What the number does not say
The difference in completed years can look different from the difference in birth years: two people born in 1988 and 1992 are '4 years apart', yet for part of every year the younger one has not had a birthday and their ages in whole years differ by 5. Leave the ages aside and compare the birth dates, as this calculator does.
How to use
Enter the two dates of birth as YYYY-MM-DD; the order does not matter, the result says who is older. Choose years, months and days, or the gap in total days, weeks, months or decimal years. Example: Person A born 1988-03-14, Person B born 1992-11-02. Step 1 (years): March 14, 1988 → March 14, 1992 = 4 years (March 14, 1993 would be after Person B's birth). Step 2 (months): March 14 → October 14, 1992 = 7 months (November 14 would overshoot). Step 3 (days): October 14 → November 2 = 17 + 2 = 19 days. Result: Person A is older by 4 years, 7 months, 19 days; 1,694 days, 242 weeks, 55.61 months or 4.64 years.
Frequently asked questions
Does it matter which person I enter first?
No. The calculator finds the earlier birth date and reports who is older, Person A or Person B, so you can enter the dates in any order.
Why is the gap 4 years 7 months when our ages are 5 years apart?
Ages in whole years jump on birthdays. Between the younger person's birthday and the older person's birthday each year, the two ages differ by one more year than the true gap. The difference between the birth dates is the exact figure.
How many days are between the two birthdays?
Choose 'Total days'. It counts the midnights between the two dates, so people born on consecutive days are 1 day apart. In the example the gap is 1,694 days.
Can I use this for the age difference with a parent, a partner or a sibling?
Yes, it works for any two dates of birth, including historical ones, as long as both are entered in the same calendar (Gregorian for modern dates).
How is a February 29 birthday handled?
The calculator uses real calendar dates. When a month in the count has fewer days than the birth day (February 29 in a common year, or the 31st in a 30-day month), that month completes on its last day.
What is the 'half your age plus seven' rule?
A rule of thumb for relationships, not a law: the younger partner should be at least half the older partner's age plus seven years. It is a social convention about current ages, which this calculator does not assess; it only measures the gap between birth dates.
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Sources & references
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