The Kelly Criterion is a method used to find the optimal stake for an investment. Ie highest stake before you are overbetting (which ultimately leads to financial ruin).

The formula is winning%-losing%/payout

E.g. if the predicted winning % is 55% and the price is $1.91, then it's 0.55-0.45/.91= 5.5%

It's a very aggressive staking strategy where bets need to be resized after each bet. You also need to know precisely what your advantage is. Most people who use this method bet a fraction of it, over 1/4 or less.

I suggest you don't use it for a number of reasons.