Position Size Calculator
Determine the right number of shares based on your risk tolerance and account size.
For educational purposes only. This calculator does not provide investment advice.
Shares to Buy
Position Value
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Risk Amount
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Risk : Reward
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📊 Visual Analysis
What This Calculator Does
The Position Size Calculator helps you determine how many shares to buy based on your account size, risk tolerance, and technical levels. It calculates the position that limits your loss to a predetermined dollar amount if your stop loss is hit.
Formula
Position size is rounded down to the nearest whole share. The Risk : Reward ratio compares potential profit (distance to target) to risk (distance to stop loss).
Input Fields Explained
Account Size ($)
Your total trading capital or account balance. This is the amount you could lose in a worst-case scenario, so be conservative.
Risk per Trade (%)
The percentage of your account you are willing to risk on this trade. 1-2% is common; never risk more than you can afford to lose.
Entry Price ($)
The price at which you plan to enter the trade. Use the current market price or your intended limit order price.
Stop Loss Price ($)
Your exit price if the trade goes against you. This should be based on technical analysis, not arbitrary. The difference between entry and stop loss determines your risk per share.
Target Price (optional)
Your profit target if the trade goes in your favor. Used to calculate Risk : Reward ratio. Leave blank if you don't have a target yet.
Example Calculation
Account: $10,000, Risk: 2%, Entry: $50, Stop Loss: $48
Risk Amount = $10,000 × 0.02 = $200
Risk Per Share = $50 − $48 = $2
Position Size = $200 ÷ $2 = 100 shares
Position Value = 100 × $50 = $5,000
At 100 shares, your maximum loss (if stopped out) is $200, or 2% of your account. The remaining $5,000 stays in cash. If you set a target at $55 (R:R = 2.5:1), your potential profit is $500.
How to Read the Result
The number of shares to purchase. Rounded down to ensure you don't exceed your risk limit.
Total capital required for the position (shares × entry price).
The maximum you can lose on this trade if your stop loss is hit.
The ratio of potential profit (to target) to risk (to stop loss). Higher is better. Enter a target price to see this.
Common Mistakes
- Setting stop loss too tight. A stop loss that's too close to your entry will get triggered by normal market noise, giving you no room to be right. Base it on technical levels, not arbitrary percentages.
- Using a stop that is too tight for volatility. Stops inside normal daily noise can trigger exits before your thesis plays out. Position size should match realistic stop placement, not arbitrary percentages.
- Risking too much per trade. Risking 5-10% per trade means a few consecutive losses can do serious damage. Most professional traders risk 1-2% or less.
- Ignoring slippage and commissions. This calculator shows the theoretical position size. In reality, slippage, spreads, and commissions reduce your real edge.
- Confusing position size with buy recommendation. Position sizing is about risk management, not identifying good trades. A well-sized position in a bad setup is still a loss.
- Adjusting size after the fact. Adding to a losing position (averaging down) to "improve" your entry often increases risk and can turn manageable losses into disasters.
When This Calculator Is Useful
- Planning trades before entry to ensure you're not over-leveraged
- Comparing risk across different trade setups to allocate capital efficiently
- Determining whether a trade fits your account size and risk tolerance
- Calculating partial exit strategies (e.g., selling half at target)
Risk Per Trade (Educational)
Many traders cap loss per trade at 1–2% of account equity. On a $50,000 account at 1% risk, the dollar risk is $500. If entry is $100 and stop is $95, risk per share is $5, so position size is $500 ÷ $5 = 100 shares (before rounding and liquidity constraints).
This is a planning framework, not a recommendation. Your risk tolerance, strategy, and regulations may differ.
Limitations
- Does not predict whether a trade will be profitable — it only manages risk if things go wrong
- Assumes stop losses are executed at the specified price; in fast markets, slippage can cause worse fills
- Does not account for correlation risk (multiple positions moving against you simultaneously)
- Position sizing alone does not guarantee trading success; you still need an edge
Continue this workflow
Keep going on the Risk & Portfolio path: open the topic hub, read the step-by-step guide, compare related calculators, and review example metrics.
Frequently Asked Questions
What is position sizing?
Position sizing is determining how many shares to buy based on your account size and risk tolerance. It ensures you don't risk more than you can afford to lose on any single trade. A common rule is to risk 1-2% of your account per trade.
How do I calculate position size?
Position Size = Risk Amount / Risk Per Share. Risk Amount = Account Size x Risk %. Risk Per Share = Entry Price - Stop Loss Price. For example, with a $10,000 account, 2% risk ($100), and $2 risk per share, buy 50 shares.
What is a good risk per trade percentage?
Most successful traders risk 1-2% per trade. Aggressive traders may go up to 3-5%, but this increases the risk of ruin. Conservative traders often stay below 1%. The key is consistency: never risk so much that a losing streak wipes out your account.
What is R:R (Risk-Reward Ratio)?
R:R compares your potential profit to your risk. A 1:3 ratio means you risk $1 to make $3. Many traders look for 1:2 or better. Higher R:R trades are more forgiving of small errors in entry timing.
How is position sizing different from portfolio allocation?
Position sizing determines how much capital to allocate to a single trade based on your risk tolerance and the trade's specific risk parameters (like stop-loss distance). Portfolio allocation is the broader strategy of dividing capital across asset classes or sectors. Position sizing is a risk management tool for individual trades, while portfolio allocation manages overall diversification.
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Educational Disclaimer
This calculator is for educational and informational purposes only. It does not provide investment, financial, tax, or legal advice. The results are based on the inputs and assumptions you provide and may not reflect real market conditions, fees, taxes, or risks. Always do your own research or consult a qualified professional before making financial decisions.