How Position Size Works: Risk Budget and a Stop
Position size turns a dollar risk limit and a stop into a share count. Wider stops mean fewer shares, so the scenario loss stays inside the budget you typed.
Key takeaways
- Risk budget = account size × risk percent.
- Shares = risk budget ÷ (entry price − stop price), rounded down to a whole share.
- A $25,000 account, 2% risk, a $50 entry, and a $47 stop is 166 shares and a $498 scenario loss if the sale fills at $47.
- A stop order can fill at a different price. The share count does not cap the loss.
The formula
Shares = (account size × risk percent) ÷ (entry price − stop price), rounded down
The stop can be a price, a percent below the entry, or dollars per share below the entry. All three become a stop price before the division. The stop has to sit below the entry. This page sizes a long position.
A worked example
Account $25,000. Risk 2%, so the budget is $500. Entry $50. Stop $47. The gap is $3 a share.
- 500 ÷ 3 = 166.67, which rounds down to 166 shares.
- Scenario loss = 166 × $3 = $498.
- Position value = 166 × $50 = $8,300.
An optional target of $56 is $6 of planned profit per share, or 2 times the $3 gap. Planned profit on 166 shares is $996. That ratio says nothing about how often the target is reached. Use the position size calculator for the same inputs.
If the gap per share is wider than the whole budget, the share count is 0. The position does not fit.
What the share count tells you
It is the largest whole-share position whose loss, at the stop you typed, stays inside the risk budget. A tighter stop allows more shares. A wider stop allows fewer.
What the share count leaves out
Gaps, halts, and a fill past the stop can make the loss larger than the scenario. Fees are not in this formula. The price that covers fees on a round trip is the break-even price. The ratio to a target is a plan, not a probability.
A company page such as Apple shows a live price you might use as the entry. It does not know your stop or your account.
For general education only. Nothing here is investment advice.
Frequently asked questions
- How do you size a position from a stop?
- Multiply the account by the risk percent, then divide by the gap between the entry and the stop. Round down to a whole share. A $25,000 account risking 2% has a $500 budget. A $50 entry and a $47 stop is $3 a share, so the count is 166 shares and a $498 scenario loss if the sale fills at $47.
- Does the share count limit the loss?
- Only in the scenario where the sale fills at the stop you typed. A stop order can fill at a different price, and a gap can skip the stop. The share count does not cap the loss.