Around one in 10 private renters are behind with their payments, according to Citizens Advice.
The charity estimates the 11% could equate to around half a million renters being in arrears, if its findings were projected across the UK.
On average, people who have fallen behind on rent now owe £730, which could potentially mean around £360 million is owed in total, Citizens Advice said.
More than half (58%) of those who were behind on rent had no rent arrears in February 2020, the survey of more than 1,300 private renters in November across the UK found.
Among people who were already struggling with rent before the coronavirus pandemic hit, 40% said their arrears had got worse.
Citizens Advice said that in December, it helped someone every two minutes typically with an issue to do with their privately rented housing.
Alistair Cromwell, acting chief executive of Citizens Advice, said: “Half a million private renters remain behind on their rent, with the majority falling behind during the pandemic restrictions.
“Unlike people who own their homes, private tenants have had no structured way to defer payments but instead have had to try to keep up with their rent and bills as best they can in a time of great uncertainty and hardship.
“Even though many landlords are trying their best to support their tenants, thousands of renters could face eviction in the coming months without further help.”