The number of people who are still living in their parents' home between the ages of 20 and 34 has increased by 20% since 1997, reports the Office for National Statistics (ONS).

London has the lowest percentage of young adults who were living in their parental home. London has a large influx of young adults from other areas of the UK and from abroad due to increased employment and study opportunities. Sharing a household with friends or housemates is more common among young adults and migrants than older adults as a way of reducing the cost of housing. In 2011 in London 6.8% of households consisted of two or more people who were unrelated, more than double the national average of 3.2%. The average (median) age of people living in such households in the UK was 25.

By contrast, the figure in Northern Ireland, at 35.3%, is the highest in the UK. A couple of factors give an indication of the reasons for the higher percentage of young adults living with parents in Northern Ireland. Firstly, the size of Northern Ireland means that it is more feasible to commute to work or university and remain living with parents than in other parts of the UK.

Secondly, the prevalence of cohabitation in Northern Ireland is around half of that observed in the rest of the UK. Conversely, the average age at first marriage in Northern Ireland is around a year lower than in England and Wales. These factors paint a more traditional picture of families in Northern Ireland, whereby young adults move out of the parental home later, cohabit less and marry earlier than in the rest of the UK. In other words, the time between leaving home and marrying may be shorter in Northern Ireland than elsewhere.

According to the ONS, young adults tend to leave the parental home earlier in the UK and other north-western European countries than in southern and eastern European countries such as Spain or Italy. The reasons for this are complex, involving differences in age at cohabitation and first marriage, income, affordability of housing and unemployment rates across different countries.