Position Size Calculator

Position sizing is the practice of determining exactly how many shares, contracts, or units to buy or sell on a given trade so that the dollar risk of the trade stays within a predefined limit relative to your total trading capital. Rather than placing an arbitrary round lot — 100 shares, 1 contract — position sizing anchors every trade to the specific risk you are willing to accept, expressed as a percentage of your account.

Professional traders treat position sizing as the single most powerful lever in their risk-management toolkit. Even a strategy with a mediocre win rate can survive and grow when position sizes are disciplined; conversely, a strategy with an excellent win rate can be wiped out by a handful of oversized losing trades. The position size calculator on this page automates that discipline by computing the exact number of shares that keeps your dollar risk at or below your chosen threshold, factoring in round-trip commissions so your real exposure matches what you intend.

The concept applies equally to equity traders managing a stock portfolio, futures traders sizing contracts, and options traders estimating capital allocation. The math is the same: define your maximum acceptable loss in dollar terms, measure the per-unit risk from entry to stop loss, and divide one by the other. Commissions reduce the shares you can safely hold because they consume part of your risk budget before the market moves at all.

This calculator displays not just the share count but a full trade scorecard — position value as a percentage of account equity, the risk-to-reward ratio, potential profit and loss, break-even price, and return on risk. Each metric helps you pressure-test a trade setup before you commit capital.

The calculator uses a fixed-fractional position sizing model. Below is the core formula along with every derived metric the calculator displays.

Step 1 — Dollar risk budget: Multiply your account balance by the risk-per-trade percentage to find the maximum dollar amount you are willing to lose on this trade.

Step 2 — Risk per share: Take the absolute difference between entry price and stop-loss price. This is the worst-case per-share loss if the stop is hit.

Step 3 — Share count: Subtract round-trip commissions from the risk budget, then divide by risk per share. The result is floored to the nearest whole share because fractional shares are not always tradable and overstating the count would exceed your risk limit.

All subsequent metrics — position value, actual risk amount and percentage, potential profit and loss, risk-reward ratio, return on risk, percent of account, and break-even price — are derived from the share count computed above.

Once the share count is established, every other metric follows directly. Understanding each one deepens your ability to evaluate a trade before you place it.

Position value is simply shares multiplied by entry price. It tells you how much capital you are deploying, not how much you risk losing — the two numbers are very different once a stop loss is in place.

Actual risk amount is recalculated from the floored share count: (shares × risk per share) + (commission × 2). Because the share count was floored, actual risk is usually a few cents below your stated risk budget. Actual risk percent is this amount divided by account balance.

Potential profit is calculated as: shares × (target price − entry price) − (commission × 2). Round-trip commissions reduce the profit side just as they do the loss side.

Potential loss mirrors actual risk amount: shares × risk per share + (commission × 2).

Risk-reward ratio is potential profit divided by potential loss. A ratio of 2.0 means you stand to gain $2 for every $1 you risk. Most professional traders require a minimum ratio of 1.5:1 to 2:1 before entering a trade.

Return on risk expresses potential profit as a percentage of your initial risk budget. This normalizes reward across trades with different risk amounts.

Break-even price is entry price plus (commission × 2) divided by shares. This is the price the stock must reach on exit just for you to recover your round-trip commission costs — a useful sanity check on tight setups.

Using the calculator effectively requires five inputs. Each one carries real consequences for the output, so it is worth understanding what you are entering and why.

Account Balance should reflect your current tradeable equity — the liquid capital available in the account for this strategy. If you trade multiple strategies from the same account, consider using only the sub-allocation for this strategy as the account balance.

Risk Per Trade (%) is the most personal parameter. Beginners often start at 1–2%. Swing traders with a proven edge may use up to 3%. Day traders with very tight stops and high-frequency entries sometimes use 0.25–0.5% per trade to accommodate multiple simultaneous positions. There is no universally correct figure — the right number is the one that keeps the largest anticipated drawdown within your psychological and financial tolerance.

Entry Price is your planned execution price. For a market order, use the current ask for a long or current bid for a short. For a limit order, use the limit price.

Stop Loss Price is the price at which you will exit if the trade moves against you. Set this based on technical analysis — below a key support level, below a moving average, or at a maximum allowed loss — not on how many shares you want to own.

Target Price is your planned profit exit. It determines the reward side of the risk-reward ratio and the potential profit calculation. A realistic target is anchored to a resistance level or a measured move, not wishful thinking.

Commission per Trade reflects one-way fees. Many brokers now offer zero-commission equity trading, in which case enter 0. For futures, options, or brokers that charge per trade or per contract, enter the actual one-way cost. The calculator doubles this figure to account for the opening and closing legs of the trade.

The mechanics of position sizing are straightforward, but applying them consistently requires understanding the broader risk-management framework in which they operate.

Fixed-fractional sizing (the model this calculator uses) means you risk a constant percentage of current equity on every trade. This has a mathematically elegant property: as your account grows, position sizes grow proportionally; as your account shrinks after losses, position sizes shrink automatically, slowing further drawdown. It is self-calibrating in a way that fixed-dollar sizing is not.

The 2% rule — risking no more than 2% of account equity per trade — is one of the most widely cited heuristics in trading risk management. It originates from the observation that a trader would need to lose 50 consecutive trades to lose their entire account, a statistical near-impossibility for a strategy with even modest positive expectancy. Most traders find this rule psychologically comfortable as well: a 2% loss on a $50,000 account is $1,000 — significant enough to feel, not catastrophic.

Maximum portfolio heat is the sum of all open positions' risk as a percentage of account equity. Even if each individual trade risks only 2%, holding ten simultaneous positions means 20% of your account is at risk if all stops are hit at once. Many risk managers cap total portfolio heat at 6–10% of equity regardless of the number of positions.

Correlation risk is another layer beyond single-trade position sizing. Two positions in the same sector, or in assets that move together during market dislocations, can both hit their stops in the same session. Treating correlated positions as a single position for risk purposes prevents concentration disguised as diversification.

Adjusting for volatility is an extension of fixed-fractional sizing. In high-volatility environments, the natural stop distance (in percentage terms) widens. A fixed-percentage risk budget will therefore reduce share count automatically — this is the model already embedded in this calculator. Some traders also scale position size inversely with the VIX or average true range to maintain consistent dollar volatility across changing market regimes.