Position Size Calculator
How many shares should you buy? Calculate position size based on your account and risk tolerance, analyze risk-reward ratios, or check total portfolio risk across multiple positions. Works with any currency.
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How to Use This Calculator
Tab "Calculate Position"
Enter your account size, risk percentage (how much of your account you are willing to lose on this trade), entry price, and stop-loss price. The calculator tells you exactly how many shares to buy, the dollar amount at risk, the total position value, and what percentage of your account the position represents.
Tab "Risk per Trade"
Enter your account size, position size (shares), entry price, stop-loss price, and target price. The result shows your dollar risk, percentage of account at risk, and the risk-reward ratio. Use this to evaluate whether a trade setup is worth taking before you enter.
Tab "Portfolio Risk"
Enter your account size and up to 5 open positions with their entry price, stop-loss, and number of shares. The calculator sums up total dollar risk across all positions and shows what percentage of your account is exposed. A warning appears if total risk exceeds 6%.
The Formulas
Risk per Share = Entry Price − Stop-Loss Price
Position size:
Position Size = (Account Size × Risk %) / Risk per Share
Dollar risk:
Dollar Risk = Position Size × Risk per Share
Risk-reward ratio:
Risk-Reward = (Target Price − Entry Price) / (Entry Price − Stop-Loss Price)
Portfolio risk:
Total Risk = Sum of (Shares × Risk per Share) for each position
Portfolio Risk % = Total Risk / Account Size × 100
All calculations are universal and pre-tax. No commissions, slippage, or country-specific rules are applied. Results are estimates.
Worked Examples
Example 1 — $50K account, 2% risk, entry $150, stop $145 = 200 shares
A trader with a $50,000 account wants to risk 2% per trade. They plan to buy a stock at $150 with a stop-loss at $145.
By risking only 2% of the account, the maximum loss on this trade is $1,000. The position itself is $30,000 (60% of account), but the actual capital at risk is capped at $1,000 by the stop-loss.
Example 2 — Risk-reward ratio of 10:1
A trader buys 200 shares of a stock at $50 with a stop-loss at $45 and a target of $100.
With a 1:10 risk-reward ratio, the trader risks $1,000 for a potential gain of $10,000. Even with a low win rate of 15%, this setup is profitable over many trades.
Example 3 — Portfolio with 3 trades = 6% total risk
A trader with a $100,000 account has three open positions and wants to check total portfolio exposure.
At 2.90% total portfolio risk, this trader is well within the 6% guideline. They could add 1-2 more positions at similar risk levels before approaching the recommended limit.
Understanding Position Sizing
What Is Position Sizing?
Position sizing determines how many shares or units to buy or sell on each trade. It is the most important risk management tool available to traders. Proper position sizing ensures that no single trade can cause catastrophic damage to your account, regardless of the outcome.
The 2% Rule
The 2% rule states that you should never risk more than 2% of your total account on any single trade. For a $50,000 account, that means a maximum loss of $1,000 per trade. This simple rule protects you from ruin: even 10 consecutive losing trades at 2% risk would only draw your account down by about 18%, leaving plenty of capital to recover.
Risk-Reward Ratios
The risk-reward ratio compares what you stand to lose versus what you stand to gain. A 1:2 ratio means you risk $1 to make $2. Higher ratios are better because they allow you to be profitable even with a low win rate. With a 1:3 ratio, you only need to win 25% of your trades to break even.
Portfolio Risk Management
Individual position risk is important, but total portfolio risk matters just as much. If you have 10 positions each risking 2%, your total exposure is 20% — a single bad day could wipe out a fifth of your account. Professional traders keep total portfolio risk under 6%, accounting for the possibility that all positions could go wrong at once.
Stop-Loss Placement
Your stop-loss determines your risk per share and therefore your position size. Place stops at technically meaningful levels — below support, below a moving average, or at a percentage below entry. Avoid setting stops too tight (you get stopped out on noise) or too loose (position size becomes too small or risk becomes too large).