Risk Management: Position Sizing

Why Position Sizing Is the Most Important Skill

You can have a winning strategy and still blow up your account with poor position sizing. Risk management determines how long you survive in the market — and survival is the prerequisite for profitability. In leveraged perpetual futures, this is even more critical because losses are amplified.

The Percentage Risk Model

The most widely used approach is the fixed percentage risk model: never risk more than a set percentage of your account on a single trade.

Common guideline: risk 1-2% per trade.

Example with a $10,000 account at 2% risk:

• Maximum risk per trade: $10,000 x 0.02 = $200
• If you lose 10 trades in a row (unlikely but possible), you lose roughly 18% of your account — painful but recoverable.
• At 10% risk per trade, 10 consecutive losses would wipe out 65% of your account.

The Position Sizing Formula

Once you know your dollar risk, calculate your position size:

Position Size = Risk Amount / Stop-Loss Distance (%)

Example: You want to long ETH-PERP at $2,000 with a stop-loss at $1,920 (4% below entry), risking $200.

• Stop-loss distance: 4% (or 0.04)
• Position size: $200 / 0.04 = $5,000
• That means you buy 2.5 ETH worth of perpetual contracts

If your stop-loss were tighter at 2%, your position would be $200 / 0.02 = $10,000 (5 ETH). Tighter stops allow larger positions for the same dollar risk.

Risk/Reward Ratio

Every trade should have a defined risk/reward (R:R) ratio before you enter.

• Risk: distance from entry to stop-loss
• Reward: distance from entry to take-profit target

Example: Long BTC at $30,000, stop at $29,500 (risk = $500), target at $31,500 (reward = $1,500).

R:R = 1:3.

With a 1:3 R:R, you only need to win 25% of your trades to break even. At 1:1, you need 50%. This is why R:R matters more than win rate.

Kelly Criterion Basics

The Kelly criterion calculates the optimal fraction of your bankroll to risk based on your edge:

Kelly % = W - (L / R)

Where W = win rate, L = loss rate (1 - W), R = average win / average loss.

Example: Win rate = 55%, average win = $600, average loss = $300.

• R = 600 / 300 = 2
• Kelly % = 0.55 - (0.45 / 2) = 0.55 - 0.225 = 0.325 (32.5%)

Full Kelly is aggressive. In practice, traders use fractional Kelly — typically 25% to 50% of the calculated value — to reduce volatility. Half Kelly here would be about 16% of the account per trade.

Stop-Loss Placement

A stop-loss should be placed at a level that invalidates your trade thesis, not at an arbitrary distance.

• For longs: below a key support level or recent swing low.
• For shorts: above a key resistance level or recent swing high.
• Add a small buffer (0.1-0.3%) beyond the level to avoid wicks triggering your stop.

Never move a stop-loss further from your entry to "give the trade more room." That is how small losses become large ones.