Position Size Calculator
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Enter your account size, the percentage you are willing to risk per trade, your entry price and your stop-loss to find the exact number of shares to buy and the value of the position. All calculations run on your device.
Why position sizing matters
Position sizing is the discipline of deciding how much to buy so that a single losing trade costs you only a set, survivable fraction of your account. Most professional traders risk a small percentage, often between half a percent and two percent, on any one idea. That way a string of losses, which every strategy has, cannot wipe out the account.
This calculator turns that rule into a concrete share count. You tell it how much of your capital you are willing to lose if the trade hits your stop, and it works out the largest position that keeps you inside that limit.
The formula step by step
First the tool computes the risk amount as your account size multiplied by your risk percentage. If you have a 10,000 account and risk one percent, that is 100 you are prepared to lose. Next it finds the risk per share as the absolute distance between your entry and your stop-loss, so an entry of 50 with a stop at 48 risks 2 per share.
Dividing the risk amount by the risk per share gives the number of shares, rounded down to a whole number so you never exceed your limit. Multiplying that share count by the entry price gives the total capital the position ties up.
- Risk amount = account size x risk percent
- Risk per share = absolute value of entry minus stop-loss
- Shares = floor(risk amount / risk per share)
- Position value = shares x entry price
Reading the results
The share count is your answer: buy that many and your loss at the stop equals roughly your intended risk. The risk amount confirms the dollars on the line, and the risk per share shows how tight or wide your stop is. The position value and its percentage of the account reveal how much buying power the trade consumes, which matters because a tight stop can produce a large position that dominates your portfolio even though the dollar risk is small.
If the position value is uncomfortably large, that is a signal your stop may be too tight for the volatility of the instrument, or that the trade needs more room.
Caveats to remember
The calculation assumes your stop-loss fills at exactly the price you set. In fast or gapping markets the actual fill can be worse, so real losses can exceed the planned figure. It also ignores commissions, slippage and the effect of leverage or margin, which change the true risk.
Treat the output as a planning baseline. Combine it with sensible stop placement based on the chart and the instrument's volatility, and never size up just because the math allows a bigger position than you are comfortable holding.
Frequently asked questions
What if my entry and stop are the same?
Then risk per share is zero and the position would be infinite, so the calculator asks you to set a stop-loss that differs from your entry before it returns a result.
Does it work for short trades?
Yes. It uses the absolute distance between entry and stop, so it works whether your stop is above your entry (a short) or below it (a long).
Should I risk one percent or two?
That is a personal risk-tolerance choice. Many traders cap risk at one to two percent per trade; more aggressive sizing raises both potential returns and the chance of a deep drawdown.
Does the position value account for leverage?
No. It shows the full notional value of the shares at the entry price. If you trade on margin, the cash required may be a fraction of that value, but your risk is unchanged.
Why is the percent-of-account figure useful?
It shows how concentrated the trade is. A small dollar risk can still tie up a large slice of your account when the stop is tight, which is worth knowing for diversification.
Can I use it for forex or crypto?
The share-based math maps directly to units or coins. Just enter prices per unit; for forex with pip values and lot sizes you may need to adjust for contract specifications.
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