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.
Position sizing works backwards from risk: instead of starting with "How many lots should I trade?", the method starts 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. In this example, the position size is chosen so 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
A stop-loss is usually placed where the trade idea becomes invalid, and the position size is then calculated around that stop. A common mistake is moving the stop just because the resulting position size is larger than the trader is comfortable with. When the required position is too large, the inputs that change are the risk percentage or the stop distance, which is a decision for each trader.
Position Sizing on a Prop Firm Account
A prop firm account adds 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?
Frequently Asked Questions
How do I calculate position size?
Decide the money you will risk (account size multiplied by your risk percentage), measure the distance to your stop, then size the position so that distance equals that amount, using the instrument's pip or point value and contract size. The same lot size can mean very different risk on different markets.
What risk percentage should I use per trade?
That is your own decision and this guide does not recommend one. The table shows how different percentages translate into money on a $10,000 account, from $25 at 0.25% to $200 at 2%. Many traders choose a figure that lets them absorb a losing streak without changing how they trade.
Is there a free position size calculator?
Yes. The free position size calculator on this site needs no sign-up and covers 19 instruments. The Position Sizer inside The Trading Terminal covers 25 instruments and is included on the Free plan.
Record the risk on every trade in a forex trading journal so you can check afterwards whether you stayed inside the size you calculated.
Built-in Position Sizer. Prop firm risk limits. Free to start.
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