The 4 Core Metrics of a Trading Strategy
Before risking real capital, every trader must answer four fundamental questions: Does this system make money? How strong is the edge? Can I survive the variance? What's the system's risk of ruin?
These four questions can be answered mathematically using just two inputs: your win rate and your reward-to-risk ratio (R). From these, we can derive everything we need to evaluate whether a trading strategy is viable in reality.
Calculate Your Strategy →Expectancy
Does the system make money?
Expectancy tells you the average profit per trade. It's the single most important number for evaluating any trading system.
Full Formula
EV = (W × AvgWin) − (L × AvgLoss) − Costs
Where:
- • W = win rate (e.g., 0.60 for 60%)
- • L = loss rate (1 − W)
- • AvgWin = average winning trade size
- • AvgLoss = average losing trade size
- • Costs = commissions, fees, slippage per trade
Simplified (in R units)
EV = (W × R) − L
When AvgLoss = 1R (your full risk) and costs are excluded. This is what theStrategy Calculator uses.
Interpretation
Expectancy > 0
Profitable system ✓
Expectancy = 0
Break even
Expectancy < 0
Losing system ✗
Example 1: Standard R
With a 60% win rate and 1.5R:
(0.60 × 1.5) − 0.40 = 0.50R
👉 On average, you earn 0.50R per trade. If you risk $100 per trade, you expect to make $50 per trade on average.
Example 2: High R
With a 30% win rate and 5R:
(0.30 × 5) − 0.70 = 0.80R
👉 On average, you earn 0.80R per trade. If you risk $100 per trade, you expect to make $80 per trade on average.
Making Average Loss Work for You
The simplified formula assumes every loss equals your full risk (1R). In practice, your average loss can be less than 1R — and this meaningfully improves your expectancy.
Ways to reduce average loss below 1R:
- • Active trade management — cutting losers early when your thesis is invalidated, rather than always waiting for your full stop to be hit
- • Trailing stops — moving stops to breakeven or partial profit on runners, turning potential full losses into scratches or small wins
- • Scaling out of losers — reducing size before the full stop is hit when price action deteriorates
If your full risk is 1R but your average loss is only 0.75R, your expectancy jumps:(0.60 × 1.5) − (0.40 × 0.75) = 0.60Rinstead of 0.50R. Over hundreds of trades, that adds up.
The Hidden Drag: Trading Costs
Costs are the silent killer of marginal edges. Every trade incurs some combination of:
- • Commissions — per-trade or per-share broker fees
- • Spreads — the bid-ask spread, especially relevant in options and forex
- • Slippage — difference between intended and actual fill price
- • Exchange fees — regulatory and exchange-level charges
These factors are shaped by your choices:
- • Broker choice — commission structures vary dramatically. A few cents per share difference compounds over thousands of trades
- • Instruments traded — large-cap stocks and major forex pairs have tight spreads; small-caps, options, and exotic pairs do not
- • Trading frequency — a scalper making 20 trades/day pays 20× the costs of a swing trader taking 1 trade/day. High-frequency strategies need much stronger raw edges to remain profitable after costs
💡 Always calculate your expectancy after costs. A system showing +0.10R per trade can easily become negative after commissions and slippage are factored in — especially for frequent traders or those using expensive instruments.
Kelly Criterion
How strong is the edge?
Kelly estimates the optimal fraction of capital to risk to maximize long-term growth. It measures edge strength—higher Kelly means stronger statistical advantage.
Formula
Kelly = Expectancy / R
or equivalently: Kelly = WinRate − (LossRate / R)
💡 Why Higher Kelly Matters
A higher Kelly percentage is your first clue to a more stable equity curve. Systems with stronger edges recover faster from drawdowns and spend more time at equity highs. This translates directly to easier trader psychology—less stress, fewer emotional decisions, and more confidence to stick to the plan during inevitable losing streaks.
Example 1: 1.5R System
With Expectancy = 0.50R and R = 1.5:
0.50 / 1.5 = 0.33 (33%)
Kelly suggests risking 33% of capital per trade.
Example 2: 5R System (30% WR)
With Expectancy = 0.80R and R = 5:
0.80 / 5 = 0.16 (16%)
Kelly suggests risking 16% of capital per trade.
⚠️ But these are far too aggressive for practical use in trading! Full Kelly assumes perfect knowledge, execution of your edge in deterministic environments, which we never have in this space. This is whereLosing Streak Expectationbecomes essential — in choosing how aggressive Kelly you can realistically be while surviving inevitable drawdowns.
Fractional Kelly in Practice
Traders typically use a fraction of Kelly to reduce volatility and account for uncertainty:
| Kelly Fraction | Risk Level | 1.5R System (33%) | 5R System (16%) |
|---|---|---|---|
| Full (100%) | Theoretical only | 33% | 16% |
| ½ (50%) | Aggressive | 16.5% | 8% |
| ¼ (25%) | Common / Recommended | 8.25% | 4% |
| ⅛ (12.5%) | Conservative | 4.1% | 2% |
Losing Streak Expectation
Can you survive the drawdown?
Even profitable systems experience runs of consecutive losses. The expected longest losing streak depends mainly on your win rate. You must size your risk so you can survive the worst-case scenario. Drawdowns can be emotionally and psychologically difficult without proper knowledge, preparation, and confidence. The ability to keep trading unaffected by drawdown is often nearly impossible, yet inability to do so reduces long-term profitability and recovery of the equity curve.This topic will have a separate article of its own.
⚠️ The Uncertain Environment
Markets are irrational with an unpredictable number of variables. Trading remains a probability game where you can do everything correctly for your edge and still lose — or worse, do things wrong and win. Losing streaks are inevitable and must be accepted and planned for to ensure the longevity of your trading profitability.
Typical Losing Streaks by Win Rate
Based on 1,000 trades — the expected and 95th-percentile worst streaks:
| Win Rate | Expected Worst Streak |
|---|---|
| 70% | 6–8 losses |
| 60% | 8–11 losses |
| 50% | 10–14 losses |
| 40% | 13–17 losses |
| 30% | 18–24 losses |
Why This Matters
Critical Formula
Risk per trade × Losing streak = Drawdown risk
Example: If you risk 4% per trade and hit an 11-loss streak (60% WR, 95th percentile):
4% × 11 ≈ 44% drawdown
Your risk must be small enough that you can psychologically and financially survive the worst expected streak.
💡 Fun Fact
Winning streaks follow the same mathematics! With a 60% win rate you can expect similar-length winning runs. This is when your account growth accelerates — knowing this helps maintain confidence during the inevitable losing streaks.
Risk of Ruin
Can the account survive long-term?
Risk of Ruin (RoR) answers a critical question: What is the probability that my account eventually goes to zero? It links your edge, position size, and long-term survival.
Formula (adjusted for R)
RoR = ((1 − E) / (1 + E)) ^ units
Where E = expectancy per unit risked, units = 100% / risk per trade
This formula accounts for the reward-to-risk ratio through expectancy. The classic (L/W)^n formula only works when wins and losses are equal size (R = 1). Since traders typically aim for R > 1, the adjusted formula gives a more accurate picture.
⚠️ The Paradox
Even a profitable system can have high probability of ruin if position sizing is too aggressive. This is why position sizing matters more than strategy for survival.
Example
With 60% win rate, 1.5R, risking 2% per trade:
Expectancy = (0.60 × 1.5) − 0.40 = 0.50R
Units = 100% / 2% = 50
RoR = (0.50 / 1.50)^50 ≈ < 0.01%
👉 Risk of ruin is essentially zero — the account is very likely to survive long-term.
Summary: Choosing Your Risk Level
While Kelly Criterion is extremely helpful in identifying the strength and stability of your edge and seeing its greatest potential, it assumes a deterministic environment. In the uncertain world of trading, considering possible losing streaks and Risk of Ruin is critical in choosing the right position sizing strategy.
| Kelly Fraction | Ruin Risk | Best For |
|---|---|---|
| Full Kelly | High volatility, significant ruin risk | Theoretical analysis only |
| ½ Kelly | Reduced but notable volatility | Well-tested, proven edge |
| ¼ Kelly | Low ruin risk, smoother equity | Most traders (recommended) |
| ⅛ Kelly | Near zero ruin risk | New strategies, uncertain edge |
💡 The Practical Approach
Start conservative, scale up with confidence. Begin with ⅛ Kelly when testing a new strategy. As you gather more data and confidence in your edge, gradually increase to ¼ Kelly. Only consider ½ Kelly after extensive live trading proves your edge is real and consistent.
Remember: A smaller position size that you can stick with through drawdowns will outperform an aggressive size that causes you to abandon the strategy emotionally.
⚠️ Disclaimer
This content is for educational and informational purposes only and does not constitute financial advice, investment advice, trading advice, or any other sort of advice. The information presented here is general in nature and is not specific to you, the user.
Trading and investing in financial markets involves substantial risk of loss and is not suitable for every investor. Past performance is not indicative of future results. You should carefully consider your investment objectives, level of experience, and risk appetite before making any trading decisions.
You are solely responsible for your own trading decisions. The author is not a licensed financial advisor, broker, or dealer. Never risk more than you can afford to lose.
The Simple Evaluation Checklist
Expectancy
Does it make money?
Kelly
How strong is the edge?
Losing Streak
Can I survive variance?
Risk of Ruin
Can I survive long-term?
Together, these four metrics tell you whether a trading strategy is viable in reality.
Calculate Your Strategy →