Nearly 65,000 London tenants left the capital in 2017 – with most joining the commuter belt, Countrywide research has found.
Popular places included Slough in Berkshire, where 46% of renters moved from the capital.
Other areas were Thurrock in Essex as well as Broxbourne and St Albans in Hertfordshire.
When it comes to buying homes after renting in London most people bought in Tandridge, Surrey, with Slough, Thurrock and Broxbourne being popular once again.
Johnny Morris, research director at Countrywide, said: “For people in their 30s leaving London is something of a rite of passage.
“But as the number of those renting has grown the move out of London is increasingly likely to be in the rental market.
“A decade ago most tenants moving out of the capital did so to buy. But since 2007 leaving London to carry on renting somewhere else has become more typical.
“Rental price growth continues to be supported by the low number of landlord purchases, particularly across the south of England.
“The number of rental homes on the market has continued to drop with more southern based landlords looking northwards in search of better yields and lower stamp duty bills.
“Conversely northern England has seen double digit increases in the number of homes on the market which is likely to temper rental growth.”