Strategy & System Design Lesson 2 of 3 10 min read

Defining Your Edge — What Expectancy Really Means

Every profitable trading strategy has a positive expectancy — the average amount you make per dollar risked over many trades. Without calculating your actual expectancy, you're flying blind. Most traders are.

What Is Expectancy?

Expectancy is the average outcome per trade, expressed as a multiple of your risk. If you risk $100 per trade, an expectancy of +0.20R means you make an average of $20 per trade over time. An expectancy of −0.10R means you lose $10 on average per trade — your strategy has negative edge regardless of how it "feels."

Formula: Expectancy = (Win Rate × Avg Win) − (Loss Rate × Avg Loss)

Where wins and losses are expressed in R-multiples (multiples of your risk per trade).

Expectancy Formula — Three Strategy Examples
Strategy A High WR, low RR Win Rate: 70% Avg Win: +1.0R Avg Loss: −1.0R E = +0.40R Profitable ✓ +$40/trade on $100 risk Strategy B Low WR, high RR Win Rate: 35% Avg Win: +3.0R Avg Loss: −1.0R E = +0.405R Profitable ✓ +$40.5/trade on $100 risk Strategy C Positive WR, bad RR Win Rate: 60% Avg Win: +0.8R Avg Loss: −1.5R E = −0.12R Losing ✗ −$12/trade on $100 risk

Notice Strategy B wins only 35% of the time — most traders would feel this strategy is "not working." But it has almost identical expectancy to Strategy A because the wins are 3× larger than the losses. Win rate alone tells you almost nothing about whether a strategy is profitable.

Where Edge Actually Comes From

Having a real edge means having a systematic reason to profit that isn't just luck. There are only a few genuine sources of edge in trading:

Sources of Genuine Trading Edge
Information Edge Knowing something others don't yet. On-chain data, order flow, macro context Analytical Edge Better pattern recognition or modelling. Backtested strategies, quant models Execution Edge Entering/exiting at better prices. Limit orders, patience, OTC access Psychological Edge Executing when others cannot. Discipline during drawdowns, no FOMO Not an Edge "A feeling" · Luck · Confirmation bias · Anecdotes · 50-trade samples

The Sample Size Problem

This is the most commonly ignored issue in retail trading: you need a large sample of trades before your results tell you anything meaningful about your strategy's actual edge.

Consider a strategy with 55% true win rate. After 30 trades, the probability of observing a win rate anywhere between 37% and 73% is statistically normal. Your 30-trade sample could show 37% wins (looks terrible) or 73% wins (looks amazing) — and both are consistent with the strategy actually being a 55% win rate system. You genuinely cannot draw conclusions from 30 trades.

Sample Size: How Many Trades Before Your Data Means Something
30 trades 37%–73% wide range inconclusive 100 trades 45%–65% better still noisy 200 trades 48%–62% good signal usable data 500 trades 51%–59% high confidence real edge visible True WR 55%

The minimum sample to draw preliminary conclusions: 200 trades. The sample where you have real confidence: 400–500 trades. This means most retail traders are making major strategy decisions based on statistically meaningless data. Their 20-trade sample showing a 70% win rate is likely noise — and so is their 20-trade sample showing a 30% win rate.

Don't Change a Strategy During a DrawdownDrawdowns are when most traders modify their strategy — adding filters, changing parameters, abandoning setups. But drawdowns within a statistically expected range are just variance, not evidence of a broken strategy. Modifying a good strategy during normal variance is the single most common way traders destroy edges they actually have.

Key Takeaways

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