Position Sizing

The one thing that actually keeps you alive. And no, "just risk 1%" is not the answer.

What it is

Position sizing is deciding how large each trade should be relative to your account. It's the most important risk management decision you make, and it happens before you enter the trade, not after.

The 1% rule, and why it's dangerous advice

Every trading course, YouTube video, and forum post repeats it: "Never risk more than 1% per trade." It sounds safe. It sounds professional. And in many scenarios, it will slowly bleed your account dry or make it mathematically impossible to reach your goals.

The problem is that 1% is an arbitrary number that ignores everything that actually matters:

• Your strategy's win rate and R:R. A scalper with a 70% win rate and 1:1 risk/reward can afford 1% per trade comfortably. A swing trader with a 35% win rate and 3:1 R:R needs completely different sizing, 1% might be too much or too little depending on the drawdown characteristics.
• Your stop loss distance. "Risk 1%" on a 10-pip stop means a massive position. "Risk 1%" on a 200-pip stop means a tiny one. The 1% rule says nothing about how exposed you actually are to market conditions, it only controls the dollar amount at the stop, not what happens between entry and stop.
• Correlation and exposure. Three "1% risk" trades on EUR/USD, GBP/USD, and AUD/USD are not 3% risk, they're closer to one big USD trade. The 1% rule counts positions, not actual exposure. You can be "safe" at 1% per trade and still have 5% of your account riding on a single dollar move.
• Gap risk and slippage. Your stop at -1% assumes the market will fill you there. It won't always. Weekend gaps, news spikes, and flash crashes blow through stops. Your "1% risk" trade can easily become a 3-5% loss on a gap. The rule gives you a false sense of precision.

Trading is a business, treat it like one

Every trading operation has two roles: the investor and the trader. The investor decides how much capital is at risk and what loss is acceptable. The trader executes within that budget. Sometimes these are two different people. Often, especially in retail, they're the same person. Doesn't matter. The roles still exist and the logic doesn't change.

• You wire $10,000 to a broker. You're the investor. You decided that $10,000 is the maximum you can lose. Now put on the trader hat, every position you take must fit within that risk budget.
• A prop firm gives you $100,000 with a 10% drawdown. The firm is the investor. They decided $10,000 is the maximum loss. You're the trader, same constraint, different source.
• A fund allocates $5M to your strategy with a 3% max drawdown. The fund manager is the investor. $150,000 is your total risk budget. Same logic, bigger numbers.

In every case, the starting point is the same: someone decided how much can be lost. That number is your entire reality. Position sizing works backwards from it.

What actually matters

Position sizing isn't a single number, it's a function of the risk budget, your strategy's behaviour, and the specific setup:

When you trade your own money, you're wearing both hats. The mistake most retail traders make is skipping the investor hat entirely, they never consciously decide "this is the maximum I can lose" and instead just start trading with whatever's in the account. That's not a risk budget, that's hope.

The prop firm version

Prop firms make the investor's decision for you, it's right there in the terms: 10% max drawdown, 5% daily limit. The risk budget is defined. Your only job is to size positions that survive your strategy's worst streaks within those limits.

Using the "1% rule" here means 5 consecutive losers hits the daily limit. Sounds safe? Five losers in a row is a normal Tuesday for most strategies. Meanwhile, the profit target demands 8-10% returns. At 1% risk with 2:1 R:R, you need ~7 net winning trades. With a 50% win rate, expect ~14 trades to get there, if the drawdown doesn't end you first.

Professional fund managers typically risk 0.25-0.5% per trade. Prop firm targets are designed for 1-2% risk, which is aggressive by institutional standards. This gap is intentional, it's why most challenges fail.

The "1% rule" is one of several trading myths explored in depth in The Lies We Trade By, a book about the trading rules everyone repeats but nobody questions, and why treating trading as a business changes everything.