The new childcare subsidy is coming. Here's what you need know.

Parents who want to keep their childcare costs as low as possible have three months to fill in an online form if they want to keep receiving government subsidies on their fees.

The new system of taxpayer subsidies starts from July 2 but the 1.2 million families who are now receiving the Child Care Benefit, Child Care Rebate or other help with paying fees will not be automatically rolled over.

To make sure they stay in the new system, parents must fill in a form via their online Centrelink account through myGov between now and July.

Centrelink will contact families over the next fortnight with instructions on what they need to do.

The new system rolls existing subsidies into a single means- and-activity-tested payment.

Parents must be working, studying, looking for work or volunteering for a minimum of eight hours a fortnight to get the new payment.

Families with annual incomes under $186,958 will no longer face a cap on the amount of fee rebate the government will pay each year.

For those earning more than this, the annual cap will lift from $7500 to just over $10,000 per child.