Working parents who earn more than £120 a week and less than £100,000 a year are eligible for the scheme if they have children aged 12 and under or under 17 for disabled children.
This will allow them to open an online account for savings used to cover childcare costs, including nurseries, childminders, after school clubs and holiday clubs.
For every £8 paid in, the government adds an extra £2, up to a limit of £2,000 per year – or £4,000 for parents of disabled children.
The scheme was launched in April 2017, but was delayed after several parents reported technical difficulties.
It has since been gradually rolled out for children by age group.
Elizabeth Truss, chief secretary to the Treasury, said:
Tax-free childcare will cut thousands of pounds from childcare bills and is good news for working parents.
More parents will be able to work if they want to and this demonstrates our commitment to helping families with the cost of living.
All eligible parents with children under 12 can now apply through Childcare Choices and should take advantage of the available support.