Newlyweds have an even earlier milestone to fear: the two-year slouch.
The poll of 5,000 couples who had been married for over a decade revealed that more than half felt undervalued.
Seven in ten men admitted they were so comfortable with their spouse they frequently left socks, pants and other dirty washing lying around the house.
Even more - 79 per cent - confessed that they no longer bothered putting the lavatory seat down.
Two thirds of the women polled said they no longer made the effort to dress up and look nice for their spouse, while 54 per cent no longer bothered wearing make-up.
Some 61 per cent admitted that they stuck on comfy tracksuit bottoms or pyjamas as soon as they got home from work.
During the first few months of marriage, 83 per cent of couples often held hands while out, compared with just 38 per cent after a decade.Partners would cuddle more than eight times a day before the first wedding anniversary - compared with five or fewer after ten years.And 60 per cent of those surveyed said they hadn't been surprised with a romantic night out since getting hitched.The infamous battle for control of the TV was another sticking point, with 75 per cent of men and women saying they wouldn't relinquish the remote control to their other half, even if they asked nicely.John Sewell, spokesman for research firm said: 'It would appear that many are stuck in a rut, and whilst they still love their other half they're a little too comfortable in each other's company.'Couples need to find a good balance between feeling comfortable and taking each other for granted.