The world's richest man is getting richer.

Bill Gates's net worth just hit $90 billion. That's roughly $AUD120 billion. He might be known for giving a lot of money away but, right now, his wealth is only increasing.

Despite his philanthropic efforts, Mr Gates still added about $15 billion to his net wealth over the past year, according to Bloomberg's Billionaires Index.

Mr Gates's net worth is reportedly equivalent to 0.5 per cent of the US GDP

Mr Gates's net worth is reportedly equivalent to 0.5 per cent of the US GDP If he was a country, Mr Gates would rank above the Ukraine with the 63rd-biggest economy in the world, according to the World Bank

If he was a country, Mr Gates would rank above the Ukraine with the 63rd-biggest economy in the world, according to the World Bank On Bloomberg's ranking of billionaires, Mr Gates has a $13-billion lead on number two, Zara majority owner Amancio Ortega



For some perspective, the Commonwealth Bank's full-year profit was $9.2 billion, Qantas posted a half-year figure of $688 million and let's not forget the world's biggest mining company, BHP Billiton, just announced it shed $8.3 billion over the past year.

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Where is Gates's money coming from?

Most of it is not coming from Microsoft.

The original (and self-described) computer nerd now owns just 2.5 per cent of the world's biggest software company, the one he co-founded after dropping out of Harvard. Those shares contribute about $11 billion to his net worth.

Mr Gates's biggest asset is a company called Cascade Investment. It invests heavily in publicly traded companies and it is these cash cows boosting the Gates's fortune.

The world's richest man is making big bucks from:

The Canadian National Railway

The Canadian National Railway The Strategic Hotel group (the owner of several Intercontinental, Four Seasons and Ritz Carlton branded hotels across the US)

The Strategic Hotel group (the owner of several Intercontinental, Four Seasons and Ritz Carlton branded hotels across the US) The not-as-luxurious waste disposal company Republic Services

The not-as-luxurious waste disposal company Republic Services Deere and Company (think: John Deere)

Deere and Company (think: John Deere) Water, hygiene and energy technology company Ecolab

So, trains, tractors, hotel rooms and rubbish. If ever there was a lesson in diversifying investments, let it be Mr Bill Gates.

But isn't he planning to give it all away?

Yes, but that isn't sending him backwards just yet.

With wife Melinda, Mr Gates set up a foundation in 2000.

Bloomberg reports Mr Gates, to date, "has donated more than $30 billion to the Bill and Melinda Gates Foundation, which so far has given away $35 billion in grants to fight hunger, disease and poverty".

The couple say they want to "take on the really tough problems".

Together with US investor Warren Buffet, also a billionaire many times over, Mr Gates also set up the Giving Pledge, which encourages the world's richest people to give at least half their fortune to charities.