It's a long time in anyone's book.
So just imagine being married for that long - it's going to involve an awful lot of compromise no matter who you are.
Happily, however, when it comes to celebrating the big 4-0 together, there's no need to compromise on the ruby anniversary gifts.
Whether you're buying for your other half, parents or friends, one way to tackle ruby wedding anniversary gifts is to go personal.
To help you out, we've highlighted our top 40th wedding anniversary gift ideas...
Original Newspapers One of the most obvious options is an original newspaper from their wedding day.
These papers aren't reprints - they're 100% authentic and as old as the date on their cover.
There are also a number of titles to choose from, including The Times and The Mirror, although availability does vary.
40th Anniversary Champagne Nothing says congratulations quite like a nice bottle of bubbly.
And in this instance you can fully personalise the label by picking one of the four designs and then adding the couple's names and a message.
In terms of the taste, you're looking at a young champagne that's light, fresh and finished with a lemony nose, lively mousse and long, crisp palate.
Engraved Crystal Glasses If you fancy supplementing your champagne, the obvious thing to do is engrave a pair of crystal glasses for the happy couple.
There's the option of champagne flutes or wine glasses, each of which can be personalised to include your couple's names, date and a brief message.
After that, we'll pack the glasses into a swish satin-lined box.
Tea at Harrods for Two As ruby wedding anniversary presents go, they don't get much swisher than tea for two at Harrods, where the celebrating couple will get to eat the tastiest sandwiches they'll have tried in 40 years.
Fillings include cucumber and minted yoghurt, smoked salmon with caper butter, and truffled egg salad with cress.
Factor in scones and pastries and it'll be an afternoon they won't forget in a hurry.
Champagne Hot Air Balloon Flight Typically offered as a midweek package, these sunrise flights are a dreamy way to see in the day.
Arriving early, you'll help set up the balloon, before rising to 2,000 feet as day breaks over your chosen county.
The whole experience lasts for about three-and-a-half hours, with one of those being spent in the sky with your other half and some champers.