Nobody puts “incompatible bedtimes” on the list of reasons a relationship fell apart. It doesn’t make the highlight reel of big fights or defining moments. It’s more of a slow bleed, one person already asleep when the other finally feels like talking, someone watching TV alone every night because their body simply won’t shut down at 10 p.m. Small stuff. Until it isn’t.

Research suggests that one in three couples are sleep incompatible, and a recent survey found that three in four couples regularly go to bed at different times. A third of them say it causes arguments. The arguments that don’t ever resolve because nobody’s technically doing anything wrong.

Robyn Alesich, a relationship expert at Sister Wives, says most couples never connect the dots. “Most couples assume relationship problems stem from communication or stress,” she told the Irish Mirror. “But they rarely consider that their body clocks might just be incompatible.”

A Relationship Expert Says Incompatible Bedtimes Could Be Causing Problems You’re Blaming on Something Else

The underlying mechanism is the chronotype, the body’s natural tendency to sleep and wake at specific times. Chronotypes are regulated by your internal 24-hour clock, which controls hormones like melatonin and cortisol and determines when you naturally feel alert versus ready to crash. Some people are wired to wind down early. Others don’t hit their peak until well after midnight. Neither is wrong, but put them in the same bed with the same schedule, and something eventually gives.

“Sleep incompatibility often threatens relationships without either person understanding why,” Alesich says. Being consistently out of sync with someone you live with accumulates. One person is always waiting, the other is always carrying a low-level guilt about it. That’s not a recipe for closeness.

Experts suggest starting small. Separate wind-down routines take the pressure off both people, so nobody’s lying in the dark waiting for sleep that won’t come, or forcing themselves to stay up for company they don’t have the energy for. Agreeing on an hour earlier in the evening that belongs to both of them gives couples the connection time that bedtime used to provide.

It sounds almost too simple. But the couples who actually try it report sleeping better and feeling closer. Given how much a mismatched bedtime can grind on a relationship over time, that’s a pretty decent win.