What this calculator adds beyond a plain date difference
The calendar math here is the same "how far apart are two dates" arithmetic behind this site's date calculator, applied specifically to two birth dates. What is different is the framing: instead of a generic day count, the result names which person is older, states each person's current age, and adds a percentage figure, the age gap divided by the older person's age. That percentage answers the question most "age difference" searches are actually asking: how big a deal is a 5-year gap, which depends entirely on how old the two people already are.
"Total days apart" and the years/months/days breakdown never change once the two birth dates are set. "Current age" and the percentage figure do change: they are both calculated as of today, in your browser, and will read differently a year from now for the same two birth dates.
Why the same number of years feels smaller as people get older
A fixed age gap shrinks as a share of either person's age the older both people get, because the denominator (the older person's age) keeps growing while the gap itself stays fixed. Two people 5 years apart are 20% apart in age at 20 and 25, but only about 8% apart at 60 and 65, the same 5-year gap measured against a much larger base. The reference table below works through several of these fixed-gap comparisons.
This is arithmetic, not a claim about how age gaps are experienced. The calculator reports the percentage; what it means for a specific pair of people (siblings, coworkers, historical figures, or a couple) is outside what a number can tell you.
The "half your age plus seven" rule of thumb
One reference point that regularly comes up in age-gap discussions is a rule of thumb holding that a person should not date someone younger than half their own age, plus seven years: a 28-year-old's floor works out to 21, and a 50-year-old's to 32. Wikipedia's article on age disparity traces variations of the phrasing back to an 1879 collection by Frederick Locker-Lampson and a 1901 book by Max O'Rell, well before its more recent circulation online, including as the "Standard Creepiness Rule" in the webcomic xkcd's 2007 strip "Dating Pools."
This calculator shows the rule's minimum age for the older person in the results, purely as the commonly cited reference point it is. It is not a scientific formula and this page does not present it as advice.
What a real spousal age gap looks like, per Census data
Married couples in the U.S. sit much closer to each other in age than a century ago. Pew Research Center's August 2024 analysis of Census Bureau American Community Survey figures found husbands and wives were 2.2 years apart on average in 2022, down from 2.4 years in 2000 and 4.9 years back in 1880, a decline that has run steadily across well over a century of censuses.
The share of couples with a sizeable gap has fallen on both sides of that average. Husbands at least three years older than their wives made up 40% of marriages in 2022, down from 43% in 2000; wives at least three years older than their husbands held at 10%, down slightly from an 11% peak in 2000. Couples within two years of each other rose from 46% of marriages in 2000 to 51% in 2022.