Mining magnate Andrew "Twiggy" Forrest will claim a tax deduction for his record $400 million donation, as he hopes his show of generosity will spur others to give away their fortunes.

Mr Forrest and wife Nicola's donation through their Minderoo Foundation is the single biggest gift by a living person in Australian history, with the money spread among six causes close to the family's heart, including cancer research and eradicating slavery.