How to Calculate Position Size: A Practical Risk Management Guide
Position sizing is one of the most important parts of risk management. The basic idea is simple: decide how much you're willing to lose first, then calculate how large the position can be.
Never start with "How many lots should I trade?" — start with "How much money am I willing to risk?"
Step 1: Determine Your Account Size
Suppose your trading account contains $10,000.
Step 2: Choose Your Risk Percentage
Imagine your predetermined risk is 0.5%. The amount you're willing to risk on this trade is:
$10,000 × 0.005 = $50 maximum planned loss
Step 3: Determine Your Stop-Loss Distance
Suppose your stop is 50 points away from your entry. Your position size must be small enough that a 50-point stop represents approximately $50 of risk. The exact calculation depends on the instrument and its contract specifications.
Risk Percentage vs Dollar Risk
| Account | Risk % | Money at Risk |
|---|---|---|
| $10,000 | 0.25% | $25 |
| $10,000 | 0.50% | $50 |
| $10,000 | 1.00% | $100 |
| $10,000 | 1.50% | $150 |
| $10,000 | 2.00% | $200 |
Don't Guess Your Position Size
This is where traders often get into trouble — picking a lot size by feel. The correct position size depends on all of the following:
- Account size
- Risk percentage
- Stop distance
- Instrument
- Pip / point value
- Contract size
- Account currency
The same lot size can represent dramatically different risk across different markets.
Calculate It Using The Trading Terminal
The Trading Terminal includes a Position Sizer designed to remove the guesswork. Instead of manually working through calculations every time, you enter your trade parameters and get the correct position size based on your predefined risk. That makes the process:
Account → Risk % → Stop distance → Position size
rather than: Position size → Hope
Position Size Should Come After Your Stop
Your stop-loss should represent where your trade idea becomes invalid. Then calculate your position size around that stop. Don't move your stop simply because the resulting position size is larger than you're comfortable with. If the required position is too large, reduce your risk percentage — not the quality of the setup.
Position Sizing for Prop Traders
Prop traders have another layer to consider. You don't necessarily have the same effective risk capacity as the headline account balance suggests. You may need to account for:
- Daily loss limits
- Maximum drawdown remaining
- Trailing drawdown
- Existing open losses
- Multiple accounts running simultaneously
The Trading Terminal's Risk Desk and Position Sizer work together to answer both questions: how much can I risk right now? — and then — how large should this trade be?
Built-in Position Sizer. Prop firm risk limits. Free to start.
Try It Free →