Position sizing is the process of deciding how many shares, contracts, lots or units to buy or sell in a trade. The calculation depends mainly on your account size, the amount you are willing to lose and the distance between your entry price and stop-loss price.
Position sizing helps prevent one losing trade from causing disproportionate damage to your account. CME Group identifies account risk and stop-loss placement as the two main inputs for calculating position size.
Position Sizing at a Glance
| Element | Meaning |
|---|---|
| Account size | Capital available in the trading account |
| Risk per trade | Maximum planned loss on one trade |
| Entry price | Price where the trade is opened |
| Stop-loss price | Price that invalidates the trade idea |
| Risk per unit | Potential loss on one share, contract or unit |
| Position size | Number of shares, contracts, lots or units traded |
How Does Position Sizing Work?
Position sizing converts a trade's planned loss into a number of shares, contracts, lots or units.
For example, assume:
- Trading account: $10,000
- Planned risk: 1%
- Maximum dollar risk: $100
- Stock entry price: $50
- Stop-loss price: $48
- Risk per share: $2
The calculation is:
Position size = Dollar risk ÷ Risk per share
Position size = $100 ÷ $2
Position size = 50 shares
The trade has a position value of $2,500, but the planned loss at the stop is approximately $100 before commissions, taxes, slippage and possible price gaps.
The stop-loss distance determines the position size. The amount available in the account does not determine it by itself.
What Is the Position Sizing Formula?
The basic position sizing formula is:
Dollar risk per trade = Account equity × Risk percentage
Position size = Dollar risk per trade ÷ Risk per unit
For a stock:
Shares = Dollar risk ÷ |Entry price - Stop-loss price|
A version that includes estimated trading costs is:
Position size = Dollar risk ÷
(|Entry price - Stop-loss price| + estimated costs per share)
Round the result down to a whole number when the market or broker does not support fractional units.
Example With Different Stop-Loss Distances
Assume a $10,000 account and a $100 risk limit:
| Entry price | Stop-loss price | Risk per share | Position size |
|---|---|---|---|
| $50 | $49 | $1 | 100 shares |
| $50 | $48 | $2 | 50 shares |
| $50 | $45 | $5 | 20 shares |
A wider stop requires a smaller position. A tighter stop permits a larger position, but a stop placed too close to the entry may be triggered by normal market volatility.
CME Group recommends placing a stop at a logical level that shows when the trade idea is wrong, rather than choosing an arbitrary distance.
How Much Should You Risk Per Trade?
The suitable risk percentage depends on your experience, strategy, drawdown tolerance and financial circumstances. Many trading plans use a small fixed percentage of account equity, such as 1%, to keep individual losses manageable.
CME Group gives 1% to 3% as an example range for newer traders, but this range is not a universal rule.
Risking 1% of a $10,000 account means risking $100 on the first trade. After five consecutive losses, the account would be approximately $9,510 if each loss equalled exactly 1% of the remaining balance. That is a loss of about 4.9%, rather than 5%, because each later risk amount becomes smaller.
A fixed-percentage approach has two main effects:
- The dollar amount at risk decreases after losses.
- The account needs a smaller percentage gain to recover from a drawdown than it would after using oversized positions.
Risking too much per trade can create a large drawdown even when the strategy has a long-term advantage.
Position Size Is Not the Same as Position Value
Position size describes how many units you trade. Position value describes the market value of those units.
For example:
- 50 shares at $50 equals a position value of $2,500.
- A stop placed $2 below the entry creates planned price risk of $100.
- The position value and the amount at risk are different measurements.
A trader can hold a large position value with limited planned risk when the stop is close to the entry. That does not remove execution risk. A stock can gap through the stop and produce a larger loss than planned.
How Does Leverage Affect Position Sizing?
Leverage allows a trader to control a position larger than the cash deposited in the trading account. It changes the margin required to open a position, but it does not remove the risk of the underlying market.
Use this process:
- Decide the maximum dollar loss.
- Select a logical stop-loss level.
- Calculate the position size.
- Check whether the required margin and total exposure are acceptable.
- Place the trade only if it fits both limits.
Starting with the maximum position offered by a broker reverses this process. The broker's margin limit is not a recommendation for how much risk to take.
FINRA and the Commodity Futures Trading Commission warn that leverage can increase both gains and losses. In leveraged forex trading, losses can require additional funds or force a position to close, depending on the account and product.
How Does Position Sizing Differ by Market?
Position sizing differs by market because each product measures risk in a different way.
Stocks
For stocks, the calculation is usually:
Number of shares = Dollar risk ÷ Risk per share
Example:
- Account: $25,000
- Risk per trade: 0.5% = $125
- Entry: $80
- Stop: $76
- Risk per share: $4
- Position size: $125 ÷ $4 = 31.25
The trader would use 31 shares if fractional shares were not available.
Forex
Forex position sizing uses the stop-loss distance in pips and the pip value of the currency pair.
Lot size = Dollar risk ÷
(Stop distance in pips × pip value)
Pip value depends on the currency pair, lot size and account currency. Confirm the pip value through your broker or trading platform instead of assuming that every currency pair has the same value.
Futures
For futures, risk per contract is generally calculated as:
Risk per contract = Stop distance in ticks × Tick value
Then:
Number of contracts = Dollar risk ÷ Risk per contract
CME Group uses this method with the contract's tick distance and tick value. A trader must also consider overnight gaps, liquidation rules, margin requirements and the substantial notional exposure that one futures contract can represent.
Options
Options require more variables because the option price can change with implied volatility, time decay, the underlying asset's price and the bid-ask spread.
For a long option, the maximum theoretical loss is generally the premium paid. A stop-loss order can still execute at a worse price during a fast market. Short options can produce much larger losses and may have theoretically unlimited loss for some strategies.
Option position sizing should account for:
- Premium paid or received
- Maximum possible loss
- Implied volatility
- Liquidity and bid-ask spread
- Assignment and expiration risk
- Gaps in the underlying asset
What Position Sizing Mistakes Should Traders Avoid?
Using the Same Number of Shares on Every Trade
Buying 100 shares on every trade creates different dollar risks when stop-loss distances vary. A trade with a $1 stop risks $100, while a trade with a $5 stop risks $500.
Choosing the Stop After Choosing the Position Size
Choose the stop from the trade setup and market structure first. Then adjust the position size to fit the risk limit.
Ignoring Gaps and Slippage
A stop-loss order does not guarantee execution at the exact stop price. Fast markets, low liquidity and overnight gaps can create a larger loss.
Treating Correlated Trades as Independent
Five positions in companies from the same sector may behave like one concentrated trade. Portfolio risk should include correlated positions, not only the risk of each position viewed separately.
Using Maximum Available Leverage
The maximum position a broker permits may be much larger than the position your account can safely withstand. Margin limits describe what you can open, not what you can afford to lose.
A Practical Position Sizing Checklist
Before entering a trade, calculate:
- Account equity
- Maximum dollar risk
- Entry price
- Logical stop-loss price
- Risk per share, contract, lot or unit
- Position size rounded down
- Estimated commissions, spread and slippage
- Total exposure to correlated positions
- Margin requirement and liquidation risk
- Maximum daily or weekly loss limit
Bottom Line
Use the position sizing calculation before placing the trade:
Position size =
(Account equity × Risk percentage) ÷ Risk per unit
The calculation does not predict market direction or guarantee that the actual loss will match the planned loss. Gaps, slippage and fast markets can change the result. It gives the trade a defined risk limit across stocks, forex, futures and options.