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Position size calculator

Decide how much you are willing to lose first, then let the arithmetic tell you how big the position can be. This calculator shows the formula and its limits.

By TokenTrail Editorial4 min read · 5 sources
Set of metal measuring spoons on a stone counter

Photo: “Measuring Spoons” by aMichiganMom, CC BY 2.0, via Flickr (edited: cropped and resized).

Quick answer

Position size = (account × risk %) ÷ (entry price − exit price). With a $10,000 account, 1% risk, entry $100 and exit $90, you risk $100 and can buy 10 units, a $1,000 position. Real exits can fill at worse prices, so losses can exceed the plan.

Key points

  • 1Start from the money you accept losing on one trade, not from how much you want to buy.
  • 2The distance between entry and exit decides the size: a wider distance means fewer units for the same risk.
  • 3A stop order is not a price promise. In fast markets it can fill below your stop, so the real loss can be larger.
  • 4If the result is bigger than your whole account, the plan only works with borrowed money — a warning sign, not a target.

Inputs

Position size

—
Money at risk
—
Units to buy
—
Position as % of account
—
Distance to stop
—

Runs entirely in your browser. Nothing you type is sent anywhere. Results are arithmetic, not advice — read the risk disclosure.

What formula does this calculator use?#

Units = (Account size × Risk % ÷ 100) ÷ |Entry price − Exit price|

The top line is the money at risk. The bottom line is how much you lose per unit if the price reaches your exit. Dividing one by the other gives the number of units at which hitting the exit costs exactly the money at risk. Position value = Units × Entry price.

The calculator also shows the position as a percentage of your account and the distance to your exit as a percentage of the entry price. These two numbers move in opposite directions: halve the distance to the exit and the position doubles for the same risk.

How does it work with the default numbers?#

StepValue
Money at risk = $10,000 × 1%$100.00
Loss per unit if the exit is hit = $100 − $90$10.00
Units to buy = $100 ÷ $1010 units
Position value = 10 × $100$1,000.00
Position as % of account = $1,000 ÷ $10,00010.00%
Distance to exit = $10 ÷ $10010.00%

Notice that the position is 10% of the account but the planned loss is 1%. Position size and risk are different numbers — this is the point of the method.

How do risk % and the exit price change the size?#

Same $10,000 account and $100 entry, computed with the formula above
Risk per tradeExit priceUnitsPosition value
0.5% ($50)$905$500
1% ($100)$9010$1,000
2% ($200)$9020$2,000
1% ($100)$805$500
1% ($100)$9520$2,000
1% ($100)$99.50200$20,000

Hypothetical inputs. The last row needs twice the account’s value — only possible with borrowed money.

Why can the real loss be bigger than planned?#

Many traders put their exit in as a stop order: an order that becomes a market order once a set price is reached [1]. The CFTC notes it is sometimes called a stop-loss order [1]. The SEC’s investor site warns that the price at which such an order is executed may differ from the stop price, especially in a fast-moving market [2]. Thinly traded assets add to the problem: crypto markets can have low liquidity, so you may not be able to sell as quickly as you would want [3].

Borrowing makes this worse. A margin account lets a broker lend you money to buy more, which raises your buying power but also exposes you to larger losses [4]. If the calculator returns a position larger than your account, read it as a sign that the exit is too close or the risk too high. See our guide to position sizing and the glossary entry on leverage.

What does the calculator leave out?#

  • Trading fees on the way in and out.
  • Gaps and slippage, as described above.
  • Whether the trade itself makes sense. The calculator sizes a plan; it does not judge it.
  • How many positions you hold at once. Five trades at 1% each can lose 5% together if they all hit their exits.

Frequently asked questions#

What risk percentage should I use?

That is a personal decision tied to your risk tolerance: your ability and willingness to lose some or all of an investment [5]. The calculator works with any value you choose.

Do I have to use a stop order?

No. The exit price can be a level where you plan to sell by hand. The arithmetic is the same; the risk is that you do not follow through.

Can I use it for long-term holdings?

Yes, as a way to ask “how much would I lose if the price fell to X?”. Set the exit to the price you are preparing for, even if it is far below today’s.

Does the calculator store what I type?

No. It runs in your browser and sends nothing to us.

The bottom line#

Position sizing turns “how much should I buy?” into “how much am I prepared to lose?”. The formula is simple; the discipline is in respecting it, and in remembering that the exit price is a plan, not a promise.

Sources#

Grade A = primary source (regulator, protocol specification, client code, original author). Grade B = expert secondary source used for explanation only.

  1. AU.S. Commodity Futures Trading Commission. Futures Glossary: A Guide to the Language of the Futures Industry, 2026.
  2. AU.S. SEC, Investor.gov. Stop Order, 2026.
  3. AEuropean Supervisory Authorities (EBA, ESMA, EIOPA). EU financial regulators warn consumers on the risks of crypto-assets, 2022.
  4. AU.S. SEC, Investor.gov. Margin Account, 2026.
  5. AU.S. SEC, Investor.gov. Risk Tolerance, 2026.