The report, Does it pay to care?, found while care workers headline pay rates were set at or above the national minimum wage of £6.19 per hour, many lost at least £1 per hour because they were not paid for the time spent travelling between appointments.
This means that in a year, a care worker who travelled an average of 35 hours per week for 48 weeks would lose £1,680.
The study comes days after the Government promised to crackdown on employers who do not pay the minimum wage. It has revised rules around the National Minimum Wage (NMW) to make it easier to name employers who fail to pay workers properly.
Resolution Foundation deputy chief executive Vidhya Alakeson said if the UK wants better home care then it needs to invest more in the workers who provide it.
"We hear a lot about the need for dignity in social care but how can we achieve that if care workers are under such pressure in their jobs and not paid even the basic wage?," she said.
The study showed there are an estimated 2 million care workers in the UK, of which 830,000 are 'domiciliary' care workers that carry out home visits. It estimated that up to 220,000 of all care workers might be paid less than the minimum wage.
Last year, minimum wage watchdog HMRC served notices to 879 employers about underpayments to staff.