HMRC intends to contact millions of people eligible for the self-employed income support scheme by the middle of May.
Those workers who have lost profits due to COVID-19 will be invited to submit online claims for payments, which will be made by early June.
The scheme provides taxable grants worth 80% of a self-employed worker's trading profits up to a maximum of £2,500 a month.
It can be claimed for an initial three months, starting from 1 March 2020, as long as trading profits were less than £50,000 in 2018/19.
Most of the UK's five million self-employed population are expected to be eligible for the scheme.
Jim Harra, chief executive at HMRC, said:
"We have the data to calculate most people's entitlement, but we need them to say whether they wish to claim as it's only open to those affected and we will need their bank details.
"I appreciate people need this money as quickly as we can possibly get it to them.
"If we can make the payments earlier, we definitely will. But mid-May is likely for when people will be able to claim."