According to the Bloomberg Billionaires Index – a daily ranking of the 100 wealthiest individuals on the planet – the world’s richest people added $US241 billion ($A229.4 billion) to their collective worth.

According to the index, Rinehart’s fortune as of December 31 totalled $18.7 billion, placing her in the 39th spot.

Rinehart’s fortune has slipped since Bloomberg’ inaugural list of the world’s richest people last year.

On October 5, Rinehart was worth $19.1 billion, making her the 36th richest person.

Her fortune at the time was down 5.4% year-on-year, equating to $1.1 billion.

Bloomberg did not give a reason for Rinehart’s latest dip in riches. But Australia’s richest person may have fallen victim to last year’s dip in the iron ore price, while her investment in Fairfax proved unrewarding.

Rinehart owns stakes in some of the biggest coal and iron ore projects in the country, through Hancock Prospecting.

Rinehart’s Hancock Prospecting owns 70% of the massive Roy Hill iron ore project, but has yet to gain financing for its development.

Bloomberg reported that the aggregate net worth of the world’s richest totalled $1.9 million as of December 31.

Others to make the list were Bill Gates at No.2, with a $63.4 billion fortune, while Asia's richest man, Li Ka-shing, took 10th spot with $29 billion.