Researchers studied interviews of more than 1,500 couples who were married or in a serious relationship.
Five years later, they followed up 1,000 of the couples to see which had lasted.
They found that if the wife was five or more years older than her husband, they were more than three times as likely to divorce than if they were the same age.
If the age gap is reversed, and the man is older than the woman, the odds of marital bliss are higher.
Add in a better education for the woman and the chances of lasting happiness improve further.