Microsoft founder and billionaire philanthropist Bill Gates says the rich should pay more taxes.

The world's richest man has had a busy day in Canberra, lobbying Prime Minister Julia Gillard to stay committed to foreign aid, meeting the Opposition Leader and speaking at the National Press Club.

He has told the ABC's 7.30 he has paid more than $US6 billion in taxes and he is glad to have done it.

"In order to deal with all the medical cost demands and other challenges in the US, as we look to raise that revenue, the rich will have to pay slightly more. That's quite clear," he said.

Mr Gates, who is worth about $US67 billion, also says the wealthy are not always the greatest philanthropists.

"The most amazing philanthropists are people who are actually making a significant sacrifice," he said.

"There's a phenomenal amount of charity from people with lower incomes, [giving] even a higher percentage of their wealth than rich people, so they're forgoing vacations or foregoing something nice.

"They're the ones that are truly charitable."

Earlier today, Mr Gates pressured the Federal Government to stay committed to its foreign aid budget after it delayed an aid increase because of poor tax revenues.

But shortly after meeting with Mr Gates, the Prime Minister announced the Government would boost funding to its polio eradication efforts by $80 million.

Mr Gates told 7.30 he now thinks his foundation is on track to get rid of the disease.

"Australia today made a new commitment that'll be a big help. There are a few more countries we'll need to go to and there's a lot of innovation being put into this," he said.

Mr Gates says wiping out polio is one of his biggest goals.

"This is something I spend most of my time on, because I think it's so important to get rid of this disease, to use this money to strengthen health systems and then go on to tackle other challenges like malaria," he said.

Focus on the 'world's greatest inequity'

Mr Gates says when he and his wife started the Bill and Melinda Gates Foundation they decided to focus on one of world's "the greatest inequities".

"Our feeling was when a child dies, a parent cares about that no matter where you are in the world," he said.

"In some sense there is no greater crime than when over 30 per cent of children in these countries are dying by age five when very, very cheap interventions - just a few per cent of what the rich world spends on their health systems... could save their lives.

"So we made that the primary focus of our foundation. We travel to see what's working, we see what isn't working, we fund brilliant scientists including a lot in Australia to do this work."

Mr Gates says he believes in "some sort of God" and he is motivated by this.

"I was brought up in the Christian church. I think the moral teachings are fantastic," he said.

"We've brought our kids up to believe those things. The golden rule captures the general spirit and so yes, I think treating others well is kind of a universal value."