How to calculate monthly trading returns?

Hey all, I'm new to trading. Sorry if this is a silly question, but how do you calculate your monthly return?

Jim Cramer (love him or hate him), said that he made 20% a month when he ran his hedge fund.

Let's say a trader has $100,000 in capital. He decides to swing trade 5 stocks. He divides his $100,000 into 5 and buys $20,000 worth of each stock (excluding commissions). He has a great month and makes 5% profit per stock in one month.

What's his monthly ROI? Is it 25%? Or is it 5%?

Making 5% on $20,000 (x5 stocks) is the same as making 5% on $100,000.

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Thanks