The top reason for staying together is for the sake of the children, which was cited by 27% of adults surveyed for counselling service Relate.
The study of almost 2,300 people comes as the charity expects a peak in calls following the festive season.
On average, Relate receives a 13% rise in calls and a 58% rise in website users each January, often peaking on the first Monday back to work and school after Christmas, sometimes known as “divorce day”.
The charity’s study of 2,298 people found 20% of those in a relationship are staying in it even though they are unhappy.
Some 26% do so because they hope things will get better, the same proportion do so because they are used to feeling that way and 24% say they cannot afford to break up.
The study found 23% stay in their relationship due to having made a commitment.
Respondents to the survey were given a list of options and asked to select all that apply to them.
Aidan Jones, Relate’s CEO, said the emotional and financial pressures of Christmas and the holidays can push couples to “breaking point”.
He added: “But, with the right support, a breaking point can become a turning point for many couples and families - whether that means working through problems together or splitting up with as little conflict as possible.”
Ruby Wax, Relate president, is supporting the #InvestInRelationships campaign, and said: “I grew up in a home where arguments and conflict were the norm - I just thought that was how relationships worked.
“Despite our ups and downs, including my own depression, I’m proud to say that my husband and I have been together for more than 30 years.
“My studies have taught me a lot about counselling and that’s been invaluable in all my personal relationships.
“Helping people to relate better is the key to happiness - and I want everyone to have access to expert support when they need it.”
The #InvestInRelationships campaign aims to ensure everyone has access to support when their relationships hit hard times, irrespective of ability to pay.