Stock Position Size Calculator

Use this position size calculator to work out how many shares to buy based on your account size, risk per trade, entry price, and stop-loss.

Account size US$

Risk per trade %

Entry price US$

Stop-loss price US$

Shares to buy —

Position value —

Amount at risk —

Risk per share —

Position as % of account —

We always strive to use the latest data for every variable so our results and reports are as accurate as possible. Even so, errors are possible — you should not rely on this tool or its report alone, and we accept no liability for any decision made based on it.

What it does

The Stock Position Size Calculator works out how many shares to buy so that a losing trade only costs a fixed slice of your account. You set the risk you accept, the entry price, and the stop-loss, and it sizes the position for you.

Data sources & parameters

This calculator uses standard financial formulas and runs entirely in your browser. It needs no external rate data — your result is computed only from the values you enter above.

The formula

shares = floor((account_size × risk_pct ÷ 100) ÷ (entry_price − stop_loss_price))

How it works

It turns your risk percentage into a cash amount, divides that by the loss per share between entry and stop-loss, and rounds down to whole shares. The result keeps every trade's downside consistent regardless of the stock's price.

Where it is used

Sizing a stock trade so one loss never exceeds your risk limit
Comparing how a tighter or wider stop changes the share count
Keeping position risk consistent across trades of different prices

Worked example

With a $100,000.00 account risking 1% per trade, an entry at $50.00 and a stop at $45.00 put … at risk. That funds … shares, a position worth ….

What the stock position size calculator does

The stock position size calculator works out how many shares to buy from the risk you are willing to take, instead of a round number or whatever cash is free. You provide your account size, the percentage you are prepared to lose on the trade, your entry price, and your stop-loss, and the tool returns the number of shares that keeps your downside inside that limit. Every position you open then carries a loss you decided in advance.

Why position sizing matters

Newer traders spend most of their energy choosing what to buy, yet how much to buy usually has a bigger effect on long-term results. A good idea sized too large can wipe out months of progress in one bad session, while a modest, disciplined size lets you survive the inevitable losing streaks long enough for your edge to show.

When every trade risks roughly the same small fraction of your account, no single loss is catastrophic and no single win is large enough to tempt you to abandon your rules, so results compound more evenly.

How the calculation works

First, your risk tolerance becomes cash. With a 100,000 account and 1% risk, your risk amount is 1,000, the most you intend to lose if the stop is triggered.

Second, the risk per share is the distance between your entry price and your stop-loss. Buy at 50 with a stop at 45 and you stand to lose 5 per share.

Third, the risk amount divided by the risk per share, rounded down to whole shares, gives the position: 1,000 divided by 5 is 200 shares. That position is worth 10,000 at the entry price, but only 1,000 of it is at risk, because the stop caps the loss.

The three inputs

Your risk budget scales with your account size, so a larger balance funds a larger position at the same risk percentage.
Risk per trade has the strongest effect: doubling it doubles both your risk amount and your share count. Most disciplined traders keep it between 1% and 2%.
A tighter stop-loss shrinks the loss per share, so more shares fit inside the same risk budget; a wider stop does the opposite. The stop is a sizing decision as well as an exit.

How to use the calculator

Enter your total account size.
Enter the percentage of the account you are willing to risk on this trade.
Enter your planned entry price.
Enter your stop-loss price.

The tool shows the number of shares to buy, the total value of the position, the cash at risk, the loss per share, and the position as a percentage of your account.

Watch that last figure. A position sized purely by risk can still be very large in money terms if your stop is tight, so check that the committed capital sits within limits your broker and your own comfort allow.

Common mistakes

Moving the stop to fit a bigger position. The stop should mark where your trade idea is wrong; sizing follows the stop, never the reverse.
Risking too much per trade. A 10% risk feels bold on a winning day and ruinous on a losing streak.
Ignoring the total position value. Risk-based sizing controls the loss, not the capital committed, and a tight stop can produce a far larger position than you intend.
Forgetting costs and slippage. Commissions and a stop that fills below your set price both add to the real loss, so leave a little headroom.

Size every trade from a fixed risk budget, keep your risk percentage steady, and let the share count follow from the maths.

This article is general information only and is not financial advice.

About This Position Size Calculator

Use this position size calculator to get an instant estimate based on the figures you enter. Adjust the inputs above to match your situation, or browse all our calculators to plan your next step.

Frequently asked questions

How does the position size calculator work?

It converts your chosen risk percentage into a cash amount, then divides that by the loss per share between your entry price and stop-loss. The result, rounded down to whole shares, is the largest position that keeps your loss within your risk limit if the stop is hit.

What is position sizing in trading?

Position sizing is deciding how many shares or units to buy so that a single losing trade only costs a fixed, pre-planned slice of your account. It ties the size of every trade to a stop-loss and a risk budget instead of a gut feeling.

How much should I risk per trade?

Many traders cap risk at 1% to 2% of their account on any single trade. The right figure depends on your strategy and tolerance, but keeping it small means a run of losses cannot seriously damage your capital.

Why does the stop-loss distance change the number of shares?

Your risk amount is fixed, so a tighter stop means a smaller loss per share and more shares fit within that budget. A wider stop means a larger loss per share, so fewer shares keep the same total risk.

What happens if my stop-loss is above my entry price?

For a long trade the stop should sit below the entry. If it is at or above the entry, the loss per share is zero or negative, no valid position can be sized, and the calculator returns zero shares.

Is my data kept private?

Yes. The calculation runs entirely in your browser. Nothing you enter is uploaded, stored, or shared with anyone.

About the author

Written and reviewed by

Taha Kheirandish

Economics student and independent researcher

Taha Kheirandish reads tax codes the way other people read maps — to find out where a system actually leads, not where it claims to go.

He is an economics student, and his work here is comparative by design. A pension deferral bonus in Quebec, a commuting allowance in Germany, a rent-increase ceiling in the Netherlands: each is a decision a government made about how money should move, and each reads differently once you set it beside eight others. He builds and checks these calculators across nine markets from primary sources — the regulation rather than a summary of it, the ministry’s own circular rather than a news item quoting it.

That is the editorial standard of the site as well as his habit. Every rate, threshold and bracket here carries the document it was read from and the date it takes effect, and gets re-checked when the law moves rather than when someone happens to notice.

He is a researcher, not a licensed adviser, and nothing on this site is personal financial advice. It is arithmetic done carefully with its sources shown — so that you can check it, and take it to someone who is.

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