Position Size Calculator
| Entry price | — |
| Stop loss price | — |
| Take profit price | — |
| Stop distance (per share) | — |
| Potential gain (per share) | — |
| Shares / units | — |
| Total position value | — |
| Max loss (incl. commission) | — |
| Max gain (at take profit) | — |
| Commission (both sides) | — |
| % of account deployed | — |
What Is Position Sizing — and Why Does It Matter?
Position sizing is the process of determining how many shares, contracts, or units of an asset to buy or sell on a given trade, based on how much of your account you are willing to lose if the trade goes against you. It is arguably the single most important element of a sustainable trading strategy — more important than your entry signal, your chart pattern, or your market view.
Without proper position sizing, even a strategy with a high win rate can blow up an account in a handful of losing trades. With it, a trader can survive long losing streaks and remain in the game long enough for their edge to play out.
The Position Size Formula
The core formula is straightforward. Given an account balance, a maximum risk percentage, an entry price, and a stop loss price, you can calculate the exact number of shares or units to trade:
Key insight: the wider your stop loss, the fewer shares you buy — keeping your dollar risk constant. Tighter stops allow larger positions. The calculator adjusts this automatically as you move the sliders.
How Much Should You Risk Per Trade?
The right risk percentage depends on your strategy, experience level, and psychological tolerance for drawdowns. Here are the commonly accepted guidelines:
- 0.5% or less — ultra-conservative; suitable for beginners or strategies with high frequency
- 1% — the professional standard; widely used by institutional and prop traders
- 2% — moderate; acceptable for experienced traders with proven strategies
- 3–5% — aggressive; can lead to steep drawdowns during losing streaks
- Above 5% — high risk; a run of ten losses at 5% each erases nearly 40% of your account
At 1% risk per trade, you would need to lose 100 consecutive trades to lose your entire account. At 5%, just 20 consecutive losses wipe you out. Most professional risk managers recommend staying at or below 2% regardless of conviction level.
Understanding Risk-to-Reward Ratio
The risk-to-reward (R:R) ratio compares how much you stand to gain on a trade to how much you stand to lose. If your stop loss is $5 below your entry and your take profit is $15 above it, your R:R ratio is 1:3 — you risk $1 to make $3.
The R:R ratio determines the minimum win rate your strategy needs to be profitable:
- 1:1 R:R — you must win more than 50% of trades to be profitable
- 1:2 R:R — you need only a 34% win rate to break even
- 1:3 R:R — you can be profitable winning as little as 26% of the time
Warning: Avoid taking trades with a R:R ratio below 1:1. Even with a high win rate, unfavourable reward ratios create a mathematical headwind that compounds over time into losses.
Long vs. Short Positions
The position size formula applies equally to both long (buy) and short (sell) trades. The key difference is the direction of the stop loss:
- Long trade — entry is above stop loss. Stop distance = Entry − Stop Loss. You profit if the price rises.
- Short trade — entry is below stop loss. Stop distance = Stop Loss − Entry. You profit if the price falls.
This calculator handles both automatically — select the direction in the toggle above and ensure your stop loss is on the correct side of your entry price.
How to Use This Calculator
- Account Balance — enter your total trading account value. Use your actual account balance, not just the capital allocated to this strategy.
- Risk Per Trade — the percentage of your account you are willing to lose if stopped out. Start with 1% until you have verified your strategy has a genuine edge.
- Entry Price — the price at which you plan to enter the trade (your buy or sell price).
- Stop Loss Price — the price at which you will exit the trade to cap your loss. This must be below entry for longs, above entry for shorts.
- Take Profit Price — your target exit price if the trade goes in your favour. Used to calculate the risk-to-reward ratio.
- Trade Direction — Long (buying, expecting price to rise) or Short (selling, expecting price to fall).
- Commission — optionally enter your broker’s per-trade commission to see its impact on your net risk and reward.
Use the Scenarios tab to compare how different risk percentages affect your position size and dollar exposure. Use the Risk Chart to visualise your trade’s potential outcomes across a range of exit prices.
Frequently Asked Questions
Most professional risk frameworks use a fixed percentage risk per trade (such as 1%) rather than a fixed number of shares. This means your dollar risk scales with your account — growing as your account grows and shrinking during drawdowns, which naturally reduces exposure when you are losing.
Trading without a predefined stop loss makes it impossible to calculate a meaningful position size, and removes the primary mechanism that protects your capital. Without a stop, even a small adverse move can escalate into a catastrophic loss. Always define your maximum acceptable loss before entering a trade.
Yes — the core formula applies to any instrument where you can define an entry price and a stop loss price. For forex, the “shares” output represents lots or mini-lots depending on your lot size convention. For futures, divide the dollar risk by the dollar value of one point move times your stop distance in points. For crypto, the result is simply the number of coins or tokens.
Commission reduces your net profit on winners and increases your net loss on losers. For small accounts or high-frequency strategies, commission drag can be significant. This calculator adds commission to your max loss calculation so you can see the true cost of the trade. To maintain your exact risk budget, some traders subtract the round-trip commission from their dollar risk before dividing by the stop distance.
The Kelly Criterion is a formula that calculates the theoretically optimal bet size to maximise long-run growth, given a known win rate and average win/loss ratio. In practice, full Kelly is extremely aggressive and leads to severe drawdowns. Most traders use half-Kelly or quarter-Kelly as a ceiling. The fixed-percentage method used here is simpler, more robust, and sufficient for most strategies — especially when your true win rate is not yet precisely known.
Yes, but you must account for correlated risk. If you hold five positions in assets that tend to move together (such as tech stocks), a market shock could trigger all five stop losses at once, creating a combined loss far larger than your per-trade risk suggests. Many risk managers cap total portfolio risk at 5–6% across all open positions, regardless of individual position sizes.