SEATTLE, July 13 (Reuters) - Microsoft Corp co-founder Bill Gates is donating $20 billion to the charitable foundation run by him and his ex-wife Melinda French Gates to boost its annual distributions.

The donation will help the Bill & Melinda Gates Foundation - one of the world's largest private charitable foundations - increase its annual payout by 50% to $9 billion by 2026, he said in a post on his personal blog on Wednesday.

"The great crises of our time require all of us to do more," Gates said, referring to the COVID-19 pandemic, the war in Ukraine and climate change, among others.

He added that the compounding effects of crises, which include surging inflation, had increased the need to invest more in the foundation's core focus areas of health, education, gender equality and poverty alleviation.

The donation brings the 22-year-old organization's endowment to about $70 billion, which includes a grant of $3.1 billion from Warren Buffett last month.