Position Sizing — The Core of Trading Risk Management

Why Position Sizing Matters

Position sizing determines how much capital to allocate to each trade. Even a high win-rate strategy can lead to ruin with poor position management. It is the most critical element of risk management.

Fixed Percentage Method

The 1% Rule

Risk no more than 1% of total capital per trade. For example, with a $10,000 account, maximum loss per trade is $100.

Calculation Steps

Determine total capital and risk percentage (e.g., 1%)

Calculate maximum acceptable loss amount

Determine stop-loss distance (entry price to stop-loss price)

Position size = Maximum loss / Stop-loss distance

Example

• Capital: $10,000 USDT
• Risk: 1% ($100)
• Entry: $50,000, Stop-loss: $49,000 (distance: $1,000)
• Position size: $100 / $1,000 = 0.1 BTC

Kelly Criterion

The Kelly formula calculates optimal bet sizing: f = (bp - q) / b

• f = fraction to invest
• b = win/loss ratio
• p = win probability
• q = loss probability (1-p)

Example: 55% win rate, 2:1 reward-risk, f = (2 x 0.55 - 0.45) / 2 = 32.5%. In practice, use half-Kelly or quarter-Kelly as full Kelly is too aggressive.

Risk-Reward Ratio (R:R)

Measures potential profit versus potential loss per trade. Aim for at least 1:2 — risking $1 for $2+ in potential reward.

Practical Tips

• Beginners should use 0.5% - 1% fixed percentage
• Reduce size during losing streaks
• Different strategies may warrant different risk levels
• Never go all-in on a single trade