Position Size Calculator
Position sizing is the number of shares or contracts you buy on a trade, calculated from your account size, risk tolerance, and stop loss level. Most professional traders risk 1-2% of their account per trade. At 1% risk on a $10,000 account, your maximum loss per trade is $100. This calculator tells you how many shares to buy to stay within that limit.
How to Calculate Position Size
The formula: Shares = (Account x Risk%) / (Entry - Stop Loss). Three variables determine the answer: your account balance, the percentage you are willing to lose, and the distance between your entry price and stop loss.
Example: $25,000 account, 1% risk ($250), entry at $50, stop loss at $48. Risk per share = $2. Shares = $250 / $2 = 125. You buy 125 shares, and if the stop triggers, you lose $250.
This works for stocks, ETFs, and crypto. You can build the same calculation in Excel or Google Sheets with =(B1*B2)/(B3-B4) where B1 is account size, B2 is risk %, B3 is entry, and B4 is stop loss.
Determine your stop and target levels before sizing the position. The stop sets your per-share risk, which drives the entire calculation.
Position Sizing Methods Compared
Fixed fractional sizing risks a constant percentage of your account on each trade. It is the most common method among active traders. Van Tharp, who wrote extensively on position sizing, considers it the foundation of trade management.
ATR-based sizing uses the stock's Average True Range to set stop distances. A volatile stock like Tesla gets a wider stop and fewer shares. A calm utility stock gets a tighter stop and more shares. The dollar risk stays constant.
The Kelly criterion optimizes position size based on your edge. It produces larger positions when your win rate and payoff ratio are strong, smaller positions when they are not.
Equal weight divides capital evenly across positions. It is the simplest method but ignores risk entirely. Two stocks with the same dollar allocation can have different risk profiles depending on their volatility and your stop distance.
How Many Shares Should You Buy?
The answer depends on three variables: account size, risk tolerance, and stop distance. There is no fixed number that works for all traders.
Beginners should risk 1% per trade. Experienced traders can risk 2%. Beyond 2%, the compounding effect of losses becomes dangerous. At 5% risk, a 10-trade losing streak destroys 40% of your account.
A single position should not exceed 5-10% of your total account value. Even if your per-trade risk is small, a concentrated position exposes you to gap risk. Practice position sizing risk-free before trading with real money.
Common Position Sizing Mistakes
Sizing based on conviction instead of math. A trader who "feels good" about a trade doubles the position size, turning a 1% risk into a 3% risk. Three bad trades at 3% risk each and the account is down almost 9%.
Ignoring correlation. Five tech stocks look like five separate positions. When the sector drops, they move together. Five correlated positions act like one concentrated bet.
Not accounting for gaps and slippage. Your stop at $48 may fill at $47.20 if the stock gaps down overnight. Build a buffer into your risk calculations. Emotional sizing destroys accounts faster than bad strategy.
Frequently Asked Questions
Frequently Asked Questions
Divide your dollar risk by the per-share risk. Dollar risk = account size multiplied by risk percentage. Per-share risk = entry price minus stop loss price. For example, on a $10,000 account risking 1% ($100), with a $2 stop distance, you buy 50 shares. The formula: Shares = (Account x Risk%) / (Entry - Stop Loss).
Start with 1% risk per trade. On a $10,000 account, that means your maximum loss per trade is $100. Enter your entry price and stop loss into this calculator, and it computes the exact number of shares that limits your risk to $100.
The 1% rule means you risk no more than 1% of your total account on any single trade. On a $25,000 account, your maximum loss per trade is $250. This keeps individual losses small enough that a losing streak cannot destroy your account.
Most retail traders hold 5 to 20 positions. Fewer than 5 concentrates risk. More than 20 dilutes returns and makes active management difficult. The right number depends on your account size, strategy, and how much time you spend monitoring positions.
ATR-based sizing uses Average True Range to set your stop loss distance. The ATR measures a stock's average daily price movement. A 2x ATR stop means your stop sits two ATR values below your entry. This method gives wider stops to volatile stocks and tighter stops to calm ones, adjusting position size automatically.
Position sizing determines how many shares to buy on a single trade. Money management is broader: it includes position sizing, risk-per-trade rules, maximum portfolio exposure, drawdown limits, and rules for scaling in or out. Position sizing is one component of a money management system.
Yes. The fixed fractional formula works for any instrument with a defined entry and stop loss. For forex, the concept is the same: risk amount divided by pip distance gives you lot size. For crypto, use the dollar values of your entry and stop.