Almost 30,000 more care home residents in England and Wales died during the coronavirus outbreak than during the same period in 2019, ONS figures show.
But only two-thirds were directly attributable to Covid-19.
The Office for National Statistics figures are the first to reveal the full toll on care homes, including deaths that happened in hospital.
Care homes in England will carry out routine testing from Monday.
There were just over 66,000 deaths of care home residents in England and Wales between 2 March and 12 June this year, compared to just under 37,000 deaths last year.
Covid-19 was the leading cause of death for male care home residents, accounting for a third of all deaths, and the second most-common cause of death for female residents, after dementia and Alzheimer's disease.
While 20,000 mentioned Covid-19 on the death certificate, another 10,000 of the excess deaths were registered to other, non-Covid, causes.
Previous analysis from the ONS has suggested that many of those "non-Covid" deaths could have involved undiagnosed coronavirus.
Three-quarters of these deaths occurred within the care homes themselves and a quarter were care home residents who died in hospitals.
A Department of Health and Social Care spokesperson said: "We have been doing everything we can to ensure care home residents and staff are protected during this unprecedented global pandemic.
"We announced today that we will be rolling out repeat testing for care home staff and residents across the country from Monday, to help further reduce the spread of infection in care homes."
Deaths from all causes in England and Wales have fallen to below the five-year average for the first time since before the coronavirus outbreak took hold, as of the week ending 19 June.
ONS figures showed deaths from all causes were lower than average for the time of year in care homes and hospitals.
The number of people dying at home was still slightly higher than average, but decreasing.
Deaths where Covid-19 was mentioned on the death certificate accounted for 8% of all deaths compared with 33% of deaths in the week ending 10 April.
Also on Friday, a survey of care homes in England which provide care for the elderly and younger people with dementia - the "Vivaldi study" - was published.
More than half of providers surveyed said they had coronavirus infections in their homes.
It also found care homes that offered their staff sick pay or relied less heavily on bank or agency staff (who may work in more than one home) had fewer infections.
From next week, residents in care homes in England for over-65s, or younger patients with dementia, will receive monthly coronavirus tests.
Staff will be tested weekly.
Any care home dealing with an outbreak, or at increased risk of an outbreak, will be more intensively tested.