The Greens are proposing to raise an extra $43 billion in taxes to pay for new spending on education, welfare and the environment.

The party is launching its election policy platform today in which it proposes a new tax of 0.2 per cent on the four major banks' assets over $100 billion.

Greens leader Christine Milne says it would raise $8.4 billion over three years.

"They have been making mega-profits, it is about time they paid their way," she said.

"The big mining companies, the big banks, the fossil fuel industry can afford to pay so that the community can be more caring."

Taxing the banks, expanding the mining tax and creating a new top income tax rate of 50 per cent for millionaires would pay for a $50-a-week increase to Newstart and a $90-a-week increase for single parents.

The Greens also want to add another $2 billion to the Government's school funding reforms and spend more on research and development and foreign aid.

"It is double the funding that Labor would have provided (for education) in the next two years," Senator Milne said.

The Greens say their policies have been costed by the Parliamentary Budget Office.

Senator Milne says her party is being upfront about how it will pay for its election promises.

"We want to make sure that we invest in the future and that the people who can help us to do that - the fossil fuel industry, the big mining companies, the big banks, the very wealthy," she said.

"They can afford to pay more so that we can invest in education and clean energy and we can help the poor out of poverty."

Senator Milne is demanding both major parties have the Parliamentary Budget Office cost their policies and release them as soon as possible.

"We'll be going to the election with a fully costed platform, and I'm calling on both the Coalition and the Government to start releasing their revenue-raising measures," she said.

"Start saying how they're going to pay for the sorts of things they're proposing."