SINGLE people beware: if and when you move in with someone, you will probably end up doing more housework. Across the rich world, men and women in couples spend more time doing housework than single people. The extra burden is greatest for women in partnerships, who do on average five more hours of housework per week than single women. Men in couples do just half an hour more. For most, household chores are boring and tedious. So why do those in couples spend more time on them, and why is the difference bigger for women?

The answer is not only that couples are more likely to have children, who create mess. Cristina Borra of the University of Seville, Martin Browning of the University of Oxford and Almudena Sevilla of Queen Mary University of London look at detailed data on how people spend their time in America, Britain and Australia. When they exclude time spent caring for children and look at couples without children, the differences remain. Perhaps, they suggest, the difference is down to the type of person who becomes part of a couple. The tidy(ing) sort might be more likely to partner up than the messy. And perhaps women in couples spend less time bread-winning, leaving more time for bread-baking.

The researchers looked at people over time, as they moved into couples, and at the differences between routine housework chores, like cooking, cleaning and tidying; and non-routine housework, like making repairs around the house. Looking at routine housework, they found that almost half the difference for women is driven by the fact that the sort to join a couple does more housework in the first place. But it is different for men. The kind of man who spurns routine housework is more likely to couple up. The extra housework such men do comes in the form of DIY or managing the family finances. The economists debunk the idea that women spend fewer hours on paid work—even when they account for differences, the chore inequality persists. It’s not that women have more time; they just do more housework.

If people in couples choose to do more housework than singletons, that is their business. Perhaps it is harder to be messy when there is someone watching over your shoulder. Well-cooked meals may be more enjoyable consumed as a pair. The gender inequality this research suggests is more concerning, however, not only in itself, but also because it could be holding back women in the workplace. Routine tasks are harder to fit around a hectic work schedule, whereas building a shelf can be done at the weekend. Men might dismiss the difference as a matter of taste, assuming, perhaps, that women prefer doing the housework, or value its fruits more highly. Women might even be responding to their partners’ possible deficiencies, at cooking, say. But women, rather than enjoying housework, may instead be responding to society’s expectations. A different study published in 2012 found that whereas the amount of housework men did seemed to vary depending on how much they hated it, women experienced no such luxury.