Age Gap Calculator

Work out the age gap

Enter two ages: you get the gap in years, the familiar "half your age plus seven" rule, and the figure that actually says something — how large the gap is relative to a life.

Person A age

Person B age

Age gap

7 years

Relative to a life

The gap is 26% of the younger person's life — and only 19% of it ten years from now.

"Half your age plus seven"

By this rule of thumb, your gap sits inside the conventional range.

At 34, the rule gives a range of 24 to 54.

The whole calculation runs in your browser.

The gap is rarely the actual subject

What strains a relationship with an age difference is usually mismatched life stages and an audience with opinions, not the number itself. Endearist helps with the part that comes after: keeping the ties that matter.

Join the waitlist →

Where "half your age plus seven" comes from

It is a piece of etiquette, not a finding. Versions of the formula have been circulating since at least the nineteenth century — it appears in French advice literature well before anyone was measuring relationship outcomes — and it has survived because it is easy to do in your head, not because anything supports it.

That is worth saying up front, because a calculator implies authority. This one reports the rule because it is what the search is for, alongside what the rule actually is: a convention about what other people will find unremarkable.

The number that means more

A gap of ten years is a completely different object at twenty and at fifty, and the rule captures this only crudely. The more useful figure is the gap as a share of a life: ten years between a thirty-year-old and a twenty-year-old is half the younger person's entire existence. The same ten years between a fifty-year-old and a forty-year-old is a quarter, and shrinking.

This is why age gaps that feel enormous in your twenties become unremarkable later without anything about the couple changing. The difference in years is fixed. The difference in proportion is not, and proportion is what life stage actually tracks.

What the research does and does not support

Being straightforward about a contested area: studies do find associations between larger age gaps and lower average relationship satisfaction or higher dissolution rates, and the effect tends to grow with the size of the gap. Those are population averages with a great deal of scatter, they cannot separate the gap itself from the reactions it provokes, and they say nothing predictive about any individual couple.

The more interesting finding is about mechanism. Where age-gap couples run into difficulty, the trouble usually traces to concrete mismatches rather than to the number: wanting children on different timelines, one person's career peaking while the other's is winding down, different energy for going out, and — consistently — the friction of an audience with opinions. Social disapproval is itself a measurable stressor, which means part of what gets attributed to the gap is caused by the reaction to it.

Why the calculator stops below eighteen

When either age entered is under eighteen, the rule is not evaluated at all. This is deliberate. A formula that returns a tidy number in that range looks like permission, and that territory is governed by age-of-consent law rather than by arithmetic from a Victorian etiquette manual.

The questions that actually predict something

If a gap is on your mind, these are more informative than any formula:

Are you on the same timeline for the big things? Children, moving, retirement, how the next decade is supposed to look. This is where most of the real trouble lives.
Does the younger person have their own footing? Their own money, their own friendships, their own opinions about the relationship. Dependence is the thing worth watching, and it correlates with a gap without being caused by one.
Who is doing the accommodating? If it is always the same person, the gap is not what is producing that.
Can you both talk about it plainly? Couples who can name the awkward parts do considerably better than couples performing that it is not there.

The last one is a conversation rather than a calculation. Our relationship check-in gives it a structure, the questions about the future cover the timeline mismatch directly, and the hard conversation planner handles the version where you have been avoiding it. And for the friendships that thin out when a relationship draws comment — a real and under-discussed cost — Endearist keeps the ties that matter on your own device.

How this test was built

This works out the exact interval between two dates of birth in years, months and days. The arithmetic is shown rather than hidden, so you can check it: the result follows directly from the figures you enter, with no weighting we have not described on this page. Where a figure comes from research rather than from you, it is named. Everything runs in your browser — no account, and nothing sent to a server.

Frequently asked questions

What is the "half your age plus seven" rule?

The rule says the youngest socially acceptable partner is half your age plus seven. At 40 that gives 27; at 26 it gives 20. It is etiquette rather than evidence — versions circulate in French advice literature from the nineteenth century, long before anyone measured relationship outcomes. It describes what other people find unremarkable, not what works.

What age gap is too big?

No research supports a single cut-off, and the honest answer depends on age rather than years. A ten-year gap is half the younger person's entire life at twenty and a quarter of it at forty — which is why gaps that feel enormous in your twenties become unremarkable later without anything about the couple changing. The calculator shows the gap as a shrinking share of a life for exactly this reason.

Do relationships with big age gaps last?

Studies do find associations between larger gaps and somewhat lower average satisfaction and stability, but the effects are modest, measured across populations, and confounded with the social cost of an unusual pairing. They describe averages, not couples. Shared life-stage goals, financial independence on both sides, and how each family reacts predict far more than the number of years.

Why does the calculator refuse ages under eighteen?

Because the half-plus-seven rule produces meaningless output below adulthood, and because age-gap questions involving minors are a legal matter rather than an etiquette one. The tool returns results for adult ages only. It is free to use, needs no signup, and the dates you enter stay in your browser.