Why a 90% Win Rate Can Still Lose You Money

What Is Risk-Reward Ratio?

When you enter a forex trade, you choose two price levels: where you will exit if the market turns against you (stop-loss) and where you will lock in a profit if the market moves in your favour (take-profit). The risk-reward ratio (often shortened to R:R) compares the distance of your stop-loss to the distance of your take-profit, measured from your entry price. If you risk 20 pips to earn 60 pips, your risk-reward ratio is 1:3. If you risk 50 pips to earn only 25 pips, the ratio flips to 2:1.

By itself, the risk-reward ratio does not tell you whether a strategy makes money. It is a structural metric: it describes the size of your potential loss relative to your potential gain on one trade. To understand whether a trading approach has an edge, you must combine it with your win rate – the percentage of trades that hit the take-profit before the stop-loss.

Why Your Win Rate Alone Is Not Enough

Many beginner traders obsess over their win rate. A strategy that wins 60%, 70%, or even 90% of the time feels safe and smart. In reality, a high win percentage can hide a fatal flaw: the average loser being far larger than the average winner. Imagine you win nine out of ten trades for a tiny gain each time, but the single loser wipes out all those gains plus more. The mathematics of profitability do not care about how many times you win; they care about the net result over many trades.

The concept that links win rate and risk-reward is expectancy. Expectancy tells you the average profit or loss per trade – in pips or in money – over a large number of repetitions. It is the only number that reveals whether a strategy has a true statistical edge. A positive expectancy means the system tends to make money over time. A negative expectancy means the account will eventually bleed out, no matter how good the win rate feels.

How to Calculate Expectancy

The formula is simple:

Expectancy = (Win Rate × Average Win) – (Loss Rate × Average Loss)

Here, win rate and loss rate are decimals (e.g., 70% = 0.70). Average win and average loss are the typical pip gains and losses per trade.

Let us work through a hypothetical example to see how win rate and risk-reward interact. Suppose two traders, A and B, each take 100 trades on EUR/USD using a mini lot, where 1 pip equals one unit of account currency (for simplicity, let us say $1).

• Trader A‘s system has an 80% win rate. The average winner earns 10 pips, but the average loser costs 50 pips. The risk-reward structure is 5:1 against the trader.
• Trader B’s system has only a 40% win rate. The average winner earns 50 pips and the average loser costs 20 pips – a reward-to-risk ratio of 2.5:1.

Now plug the numbers into the expectancy formula.

Trader A:

Expectancy = (0.80 × 10) – (0.20 × 50) = 8 – 10 = -2 pips per trade.

Trader B:

Expectancy = (0.40 × 50) – (0.60 × 20) = 20 – 12 = +8 pips per trade.

After 100 trades, Trader A would lose approximately 200 pips, while Trader B would gain about 800 pips. Even though Trader A won twice as many trades, the enormous losing trades erased all the small wins. Trader Bs lower win rate, paired with a healthy risk-reward structure, produced a solid positive expectancy. (All numbers are hypothetical and for educational illustration only – no real trades are implied.)

Common Misconceptions and Limitations

• High win rate equals a good strategy. A 90% win rate can still deliver a negative expectancy if the average loss is ten times the average win. The balance between how often you win and how much you win is what matters.
• A fixed risk-reward ratio guarantees profit. Even a 1:3 reward-to-risk ratio can fail. If the win rate is only 20%, the expectancy becomes (0.20 × 3R) – (0.80 × 1R) = 0.6R – 0.8R = –0.2R, which is still negative.
• Expectancy is a guarantee of future performance. Expectancy is a long-term average. In the short run, random variance can produce long losing streaks that test any system, even one with a strong positive edge. Proper position sizing and emotional discipline are required to survive those streaks.
• Transaction costs can flip a borderline strategy. Spreads, commissions, and slippage eat into every trade. If the pre-cost expectancy is only slightly positive, real-world trading costs might turn it negative. Always account for realistic costs when evaluating any hypothetical system.

What This Means for Your Trading Journey

Understanding expectancy does not hand you a profitable system – it hands you a way to evaluate one. Before risking real capital, many traders backtest a strategy over hundreds of hypothetical trades, estimating the likely win rate and average win and loss. Only then can they calculate whether the expectancy is positive and whether the system is likely to survive inevitable losing runs.

Risk management is the other half of the equation. Even a strategy with a positive expectancy can destroy an account if the trader risks too much per trade. A string of five or six consecutive losses – a perfectly normal outcome for a 50% win rate system – can cut an account in half if each trade risks a large fraction of the balance. Most educational resources suggest limiting risk per trade to a very small percentage of the account, such as 1% or 2%, but the right number depends entirely on the individual, their system, and their tolerance for drawdowns. The key is to choose a risk amount that lets you continue trading after a tough patch without emotional panic.

Finally, beware of the psychological comfort of a high win rate. A strategy that wins most trades but suffers rare, catastrophic losses lulls you into a false sense of safety. By the time the large loss arrives, it may be too late to adjust. Checking the expectancy of a strategy – not its win percentage – is the first line of defence against this hidden trap.