Free age difference calculator
Find the exact age difference between any two people — enter both birth dates and see the gap in years, months, and days, with leap years and uneven month lengths handled automatically. Perfect for couples, siblings, friends, or family, and updated live, as you type.
On this page13 sections
Date calculations use calendar days. Working days exclude weekends but not public holidays unless noted.
Results are estimates. Consult a professional.
What is an age difference?
An age difference — or age gap — is simply how much older one person is than another, measured from their two birth dates. This age difference calculator takes both birth dates and returns the gap broken down into years, months, and days, automatically handling leap years and uneven month lengths so the result is exact rather than a rough estimate.
Because it works from dates of birth, the order you enter them in does not matter: the calculator always reports the gap between the earlier date and the later one. The same tool answers "how many years apart are two siblings," "what is the age gap between a couple," or "how much older is one twin than the other" — any time you need the precise distance in time between two people.
How the age difference is calculated
The calculator does not just subtract the two birth years — that would ignore the months and days and can be off by almost a full year. Instead it counts the calendar distance from the older person's birth date to the younger person's birth date, the same way you would work out someone's age. The method is a three-step subtraction that borrows across months when needed:
- Subtract the days. Take the younger birth day-of-month minus the older birth day-of-month. If the result is negative, borrow one month: add the number of days in the preceding month, and reduce the month count by one.
- Subtract the months. Younger birth month minus older birth month (after any borrow above). If this is negative, borrow one year: add 12 months and reduce the year count by one.
- Subtract the years. Younger birth year minus older birth year (after any borrow). What remains is the whole-year part of the gap.
A worked example: the age gap between two siblings
Maya was born on 15 March 2010 and her younger brother Sam on 20 September 2013. Here is exactly how the calculator finds the gap between them.
Step 1 — Subtract the days
20 (Sam's day) − 15 (Maya's day) = 5 days. The result is positive, so there is no need to borrow a month — the day part of the gap is 5.
Step 2 — Subtract the months
September is month 9 and March is month 3, so 9 − 3 = 6 months. Still positive, so there is no year to borrow — the month part is 6.
Step 3 — Subtract the years
2013 − 2010 = 3 years. Putting the three steps together, the age difference is 3 years, 6 months, and 5 days. (Expressed purely in days, that same gap is 1,285 days.)
When you first open the tool it is pre-filled with 1 January 1990 and 1 January 2020 — a clean 30-year gap (30y 0m 0d apart) you can verify at a glance before entering your own dates.
Years, months, and days — and total days
The headline figure is the whole-year part of the gap; the line beneath it gives the full years, months, and days breakdown. People often want the same gap in a single unit too — total days, weeks, or even hours — which you can derive from the breakdown or read directly from a dedicated tool.
| Birth date A | Birth date B | Headline gap | Full breakdown | Total days |
|---|---|---|---|---|
| 1 Jan 1990 | 1 Jan 2020 | 30 years | 30y 0m 0d | 10,957 |
| 15 Mar 2010 | 20 Sep 2013 | 3 years | 3y 6m 5d | 1,285 |
| 20 Jul 1985 | 5 Nov 1990 | 5 years | 5y 3m 16d | 1,934 |
Three age gaps as the calculator reports them. The headline shows whole years; the breakdown adds the leftover months and days. Total days is a derived figure (the tool's own readout is years/months/days).
If you only need the raw day count between two dates, the days between dates calculator gives it directly, while the age calculator applies this same method to a single person against today's date.
Common uses: couples, siblings, and friends
Because it works between any two birth dates, the age difference calculator gets used for far more than curiosity. The most common cases all share the same maths but ask the question for different reasons:
- Couples and partners — the classic "how big is our age gap" question, answered to the exact day rather than a rounded number of years.
- Siblings — how far apart brothers and sisters are, useful for spacing-of-children questions or just settling who is older by how much.
- Friends, colleagues, and classmates — the gap between two people in a group, or between a person and a public figure.
- Family trees and milestones — comparing generations, e.g. the gap between a parent and child or between cousins.
For single-person date questions — "how old am I," "how many days have I been alive," or "how long until my next birthday" — see the days alive calculator and the birthday countdown, which use the same calendar engine.
The “half your age plus seven” rule
A widely-quoted social rule of thumb describes the age range many people consider a comfortable gap for a relationship: take your age, halve it, and add seven to get the youngest end; reverse the formula — subtract seven, then double — to get the oldest end. It is a cultural guideline, not a law or a recommendation, but it is the reason this question comes up so often alongside the calculator.
| Your age | Youngest (½ + 7) | Oldest (−7, ×2) | Range width |
|---|---|---|---|
| 20 | 17 | 26 | 9 years |
| 30 | 22 | 46 | 24 years |
| 40 | 27 | 66 | 39 years |
| 50 | 32 | 86 | 54 years |
| 60 | 37 | 106 | 69 years |
The “half plus seven” range widens as people get older. Figures are arithmetic from the formula above; treat them as a talking point, not advice.
How big are typical age gaps between couples?
Once you have your own number, it is natural to ask how it compares. A large study published in Population Studies analysed recent census and survey data across 130 countries and found that, worldwide, men are on average 4.2 years older than their wives or cohabiting partners — but the figure varies widely by region.
| Region / group | Average age gap (men older) |
|---|---|
| Worldwide average | 4.2 years |
| North America | 2.2 years |
| Sub-Saharan Africa | 8.6 years |
Average age difference between men and women in different-sex couples, from a 130-country analysis of census and survey data (Population Studies, 2022).
In other words, a gap of two or three years is close to the North American norm, while gaps of eight years or more are common in some regions and rare in others. Your own figure from the calculator is just a fact about two birth dates — the averages simply give it context.
Common age difference questions
Does the order I enter the two birth dates in matter?
No. The calculator automatically counts from the earlier (older) birth date to the later (younger) one, so you can enter the two dates in either order and get the same age gap.
Why is the gap shown in years, months, and days instead of just years?
Because rounding to whole years can be off by almost a full year. Two people born 11 months apart are not “the same age” — the months-and-days breakdown shows the true distance, the same way an exact age is more precise than a rounded one.
Does it account for leap years?
Yes. The gap is counted across the real calendar, so any 29 February that falls inside the span is included. That is why two gaps that look the same in years can differ by a day in total. See the leap year calculator for how leap days work.
How this calculator works and sources
This age difference calculator counts the exact calendar distance between two birth dates and reports it in years, months, and days, borrowing real month lengths and including leap days exactly. All of the maths runs in your browser — the two dates are never sent anywhere. The years/months/days subtraction method is the same standard approach used to compute a person's age; the relationship-statistics figures and the half-your-age-plus-seven rule are widely documented and cited below.
Pirani & Schoumaker, “Measuring age differences among different-sex couples across religions and 130 countries” — Population Studies (2022), via PubMed.Psychology Today — What Is the Average Age Gap in Relationships Worldwide?Frequently asked questions about the free age difference calculator
About this age difference calculator
This age difference calculator runs entirely in your browser. The two birth dates you enter are never uploaded or stored anywhere — the years/months/days gap is computed locally and updates instantly as you change either date, so nothing about the two people involved leaves your device.
It is part of the everyday tools on our everyday calculators shelf, alongside the age calculator, days between dates calculator, and leap year calculator. Browse the full calculators directory for hundreds more.