It has traditionally been the time when love and affection give way to disillusion and disappointment.
But couples who manage to survive the seven-year itch would be wise not to get complacent.
The biggest threat to modern marriages actually comes from the 12-year itch, research has revealed.
The majority of couples who divorce have now spent more than a decade together before going their separate ways.
And they are increasingly likely to cite "growing apart" or "falling out of love" as the cause of their split.
There has been a four-fold increase in couples breaking up for these reasons in the last two years, amid increasing financial strain on families.
But infidelity is still responsible for more than a quarter of divorces. The seven-year itch - or the theory that adultery becomes impossible to resist after seven years - got its name from the 1950s film starring Marilyn Monroe.
The study by the Grant Thornton accountancy group, which was based on a survey of 90 of the country"s biggest family law firms, echoed figures released last year which showed that marriages are most likely to fall apart around the 12-year mark.
Sally Longworth, of Grant Thornton"s Forensic and Investigation Services, said: "This rather dispels the age-old myth about marriages failing after seven years.
"It is impossible to put any scientific reasoning on why certain marriages succeed and others fail."