What is Position Sizing in Trading?
Position sizing is the process of calculating how many lots or units to trade so that your dollar risk per trade stays within a percentage you define based on your own risk tolerance.
How It Works
The position sizing formula is: Lot Size = (Account Balance x Risk %) / (Stop Loss in Pips x Pip Value). Say your account is $10,000, you choose to risk 1% ($100), your stop is 25 pips, and the pip value on EUR/USD is $10 per standard lot, your position size is $100 / (25 x $10) = 0.4 lots. Position sizing adjusts automatically with your account size. As you grow, your dollar risk per trade increases while the percentage stays constant. During drawdowns, position sizes shrink, protecting you from catastrophic loss streaks. Some traders use fixed fractional sizing (constant percentage), while others use fixed dollar amounts. The percentage method is generally preferred because it's self-correcting: it scales down during losses and scales up during profits.
Why It Matters
Position sizing matters more than your strategy. Without it, a trader with a great system can still blow up by oversizing on a single bad trade. With it, even an average strategy survives long enough to compound.
Common Mistake
Risking more on trades that 'feel' high-conviction. Every trade feels high-conviction at entry. That's why you took it. Varying risk based on subjective confidence tends to produce the largest losses on the largest positions.
Example
Account: $5,000. Risk per trade: 2% ($100). Stop loss: 40 pips on GBP/JPY. Pip value on 1 standard lot: ~$6.60. Position size: $100 / (40 × $6.60) = 0.38 lots (round to 0.4 on platforms that only allow 0.1-lot increments).
Stoic Insight
Temperance, the Stoic virtue of self-restraint, is position sizing in practice. It asks 'what can I afford to lose?' before asking 'what could I gain?' The disciplined answer to that question determines everything that follows.
Related Terms
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