Shouldn't the spread be added to the numerator instead of subtracted?Random win probability
I often like to calculate the random win probability of my strategies to see whether it's luck or an edge:
First, we need to calculate the probability of a trade to become a winner.
Here's the formula: (average loss - average spread) / (avrg loss + avrg win)
My strategy: (42.45 - 1.5) / (42.45 + 22.3) = 0.632
This means that a trade has a random probability of 63.2% to become a winner.
Shouldn't the spread be added to the numerator instead of subtracted?
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According to the link I posted above, the calculated value is the break-even win rate.It should be subtracted, and here is why: spread shifts our entry against us, therefore TP is harder to reach. The probability to reach it with spread=0 should be higher, than with spread>0.
Let's check two examples that both have SL=TP=10 pips. The 1st has no spread and the 2nd has spread=1.
1. Spread=0: (10-0)/(10+10)=0.5 : The probability to reach TP is 50%
2. Spread=1: (10-1)/(10+10)=0.45 : Here, when we do have spread, the probability to reach TP is lower - 45%
**Key caveat:** You cannot calculate your *empirical win probability*—the actual chance that any single trade is a winner—without knowing either the number of winning trades or the win rate from past data[3][4][5]. You can only determine the *break-even* win rate using averages[6].
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[3] https://www.quantifiedstrategies.com/trading-probability/
[4] https://www.quantifiedstrategies.com/win-rate-trading/
[5] https://www.luxalgo.com/blog/win-rate-and-riskreward-connection-explained/
[6] https://market-bulls.com/breakeven-win-rate-calculator/
According to the link I posted above, the calculated value is the break-even win rate.
So, for SL=TP=10 pips comparing zero spread and spread=1,
- Spread=0: (10+0)/(10+10)=0.5 : The break-even win rate is 50%.
For example, 20 trades with 10 wins and 10 losses (50% win rate) breaks even ((10 * 10) - (10 * 10) = 0).- Spread=1: (10+1)/(10+10)=0.55 : With the spread included, the break-even win rate is a higher 55%.
For example, 20 trades with 11 wins, 9 losses, and 20 spreads (55% win rate) breaks even ((11 * 10) - (9 * 10) - 20 = 0).
It's not possible to calculate the probability of reaching a target point given only average win, average loss, and average trade cost.
You are correct for a random walk model if all trades have the same target, stop, and spread.Please, paste my previous reply to the language model that you are using. We are not looking for a break-even rate of the entire strategy. We are looking for the probability of any given random trade to become a winning trade (you can tell this to the language model, and it will understand its mistake).
Summary: Using only averages, you can estimate expectancy, not the underlying probability of each trade winning—unless your trading strictly follows the random walk model with fixed TP, SL, and cost for all trades. Most trading reality is more complex.
You are correct for a random walk model if all trades have the same target, stop, and spread.