Three formulas that will change how you size every trade.
Risk of ruin is the probability that consecutive losses wipe your account. Three inputs decide it: edge, risk per trade and number of trades. Plug them into Kelly to see why most retail traders blow up not because their setups are wrong, but because their size is wrong.
The formula
R = ((1 − A) / (1 + A))^U, where A is your edge per trade and U is your starting bankroll in R-units.