Most traders blow up not because their ideas are terrible, but because their position sizes are reckless. Position sizing is how you control risk. Get it wrong, and even a good strategy can’t save you. Get it right, and you give yourself enough room to let your edge play out.
The Core Idea
Never risk too much on one trade. A common rule is to risk 1%–2% of your account on any single idea. That doesn’t mean 1% of your money goes into the trade. It means if you’re wrong, your loss should be 1% of your account at most.
Example
Account size: $10,000
Risk per trade: 1% = $100
- Stock entry: $25
- Stop loss: $24
- Risk per share: $1
- Shares to buy: $100 ÷ $1 = 100 shares
You’ve capped your downside. Even if you’re wrong ten trades in a row, you’re down ~10%, not wiped out.
Why It Matters
- Preserves capital: Without sizing discipline, a single bad trade can knock you out.
- Takes the emotion out: If you know the maximum loss ahead of time, you stop making panic decisions mid-trade.
- Lets the math work: You don’t need to be right 70% of the time. With proper sizing and solid risk/reward, you can win with 50% or even 40% accuracy.
Common Mistakes
- All-in trades: One wrong move and the account is gone.
- Sizing by “feel”: Adding more because you “like this trade” isn’t discipline — it’s gambling.
- Moving stops after entry: That breaks the whole math. Your sizing is based on your stop. Widening it on the fly increases risk without increasing potential reward.
How to Apply It
- Decide risk first. Always define your stop before entry.
- Calculate how many shares or contracts keep the loss within your limit.
- Stick to the formula. No exceptions because “this setup looks great.”
Final Thoughts
Position sizing is boring. It doesn’t feel like calling direction or picking winners. But it’s what separates traders who survive from traders who blow up. You don’t have to predict the market every time — you just have to make sure that when you’re wrong, you live to trade the next setup. That’s how compounding starts to work in your favor.