Position size calculator: how many shares match your risk?

Short answerPosition size is how much of a stock you hold. To work it out from risk, take the amount you are willing to lose and divide it by what each share loses between the entry price and the exit price. The answer is the number of shares.

How to work out your position size

You need four numbers: the size of the account, the share of it you are willing to lose on the trade, the price you buy at and the price you sell at if it goes wrong. An example:

The account holds $10,000 and you are willing to lose 3 percent of it. That is $300.
You buy at $50 and sell at $47 if it goes wrong. Each share then loses $3.
$300 divided by $3 is 100 shares. They cost $5,000, which is half the account.

The 3 is there so that the sum comes out even.

Work it out

Account size, $Share you are willing to lose, %Entry price, $Exit price if it goes wrong, $

Shares–

The shares cost–

Loss at the exit price–

Share of the account–

How much of your account should you risk?

No sum can answer that, and this page suggests no percentage. Trading books often name a round number, but that number is a habit and not the result of a calculation. The answer depends on what the money is for, how many trades you have open at once and how many losses in a row you could stand.

The last one you can work out. Ten losses in a row, each of 3 percent of what is left, leave 74 percent of the account. Put in your own percentage and multiply the same way.

Why does a wider exit give fewer shares?

The amount you are willing to lose stays the same, but each share can lose more. If you sell at $38 instead of $47, each share loses $12, and $300 then covers 25 shares for $1,250. The position is a quarter of the size, and the loss at the exit price is the same.

That is why positions are often smaller in a stock that moves a lot. With an exit close to the entry, ordinary moves can reach it with nothing having happened at the company. One way to set the distance from how much a stock usually moves is average true range.

Can you lose more than the sum says?

Yes. The sum only holds if you get to sell at the exit price. A stop order becomes a market order when the price is reached, and it fills at whatever price is there at that moment. The SEC notes that this price can differ from the stop price, especially when prices move fast. If the stock opens at $40 after bad results, each share loses $10. On 100 shares that is $1,000, not $300. Real stocks have fallen this much in a single day.

If the account does not stretch that far

With an exit close to the entry, the sum can ask for more shares than the account can buy. If you sell at $49.50, each share loses 50 cents, and $300 becomes 600 shares for $30,000. The account covers 200 shares, and the loss at the exit price is then $100. The calculator says so when that happens.

How the calculator works

The number rounds down to whole shares, so the loss can be slightly less than the amount you chose.
The page works with shares you buy. Short selling is not covered.
Fees and tax are not counted.
The numbers sit in the link, so anyone who gets the link sees them. No prices are fetched.

Source

U.S. Securities and Exchange Commission, Stop Order, read 5 November 2026.

Have you already bought in several rounds? Work out your average cost.