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What edge means, the expectancy calculation, and the casino lesson every trader can use
Published by The Retail Trader · AUG 09, 2026 · Features
A casino does not win every hand. It loses nearly half of its hands. Even so, it is always ahead at the end of the year, because it has a small mathematical advantage on every hand and it plays a great many hands. In trading, this advantage is called edge.
Edge does not mean you are right more often. It means that the math of your being right and wrong, combined with size and frequency, comes out positive.
So 'I'm right 80% of the time' is not a claim in itself. If the 20% of losses is bigger than the other 80% of wins, the edge is negative.
Expectancy = (win rate × average win) − (loss rate × average loss). This is the average result per trade.
An example, in terms of R (R = the risk of one trade):
• 40% of trades win, average win 2R — that is 0.40 × 2 = 0.80R.
• 60% of trades lose, average loss 1R — that is 0.60 × 1 = 0.60R.
• Expectancy = 0.80 − 0.60 = +0.20R per trade.
• That means about +20R over 100 trades, if everything goes the same way. And that 'if' is the real work.
A real edge is almost always small. A system that claims to win 'every trade' has either not yet met its bad patch, or is being sold to you.
A small edge is not worthless. A small edge, enough trades, and steady size — these three together build the result over the long run. Without any one of them the other two do not work.
First: cost. Charges and slippage on every trade cut directly from expectancy. An edge of +0.2R, if each trade costs 0.1R, is halved.
Second: changing size. Losing on big size and winning on small size sinks the account despite your beautiful win rate.
Third: changing systems. Adopting a new method with every bad patch means never giving any edge a chance to work.
Markets change and edges wear down. That is why a journal and periodic review are not just discipline — they are the way to find out whether your advantage is still alive. And on the day it is not, the best trade is to take no trade.
This article is for educational purposes only — it is not a buy or sell recommendation, makes no claim of guaranteed returns, and is not advisory. Rules, rates and mechanics change from time to time at the exchanges, SEBI and RBI, so verify every number yourself with your broker or an official source.