PositionSizeTools

Position Size Calculator

Size a stock or share position from account risk and stop distance, with the risk actually taken and the position as a share of the account.

Last reviewed

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Free · No sign-up · Runs in your browser

Position size is not a matter of conviction, available capital or how good the setup looks. It is a division: the amount you are willing to lose, divided by the distance to the stop. Everything else is decoration.

This calculator performs that division and reports what it implies - the number of units, what the position is worth, what percentage of the account it represents, and the risk actually taken after rounding down to whole units. It works the same way for shares, contracts for difference and any instrument sized in units.

Your numbers

Results update as you type. Nothing is sent anywhere.

Result

Position size (units)

204

Position value
$8,670
Risk budget
$500
Risk actually taken
$500
Risk per unit
2.4
Stop distance
5.65%
Position as a share of the account
17.34%
Break-even price after fees
42.55
Direction
Long

This tool is for informational and educational purposes only. It is not financial or investment advice, and past performance does not guarantee future results.

Position size is decided by the stop distance, not by conviction. A wider stop always means a smaller position for the same risk.

The result is rounded down to whole units so the risk never exceeds the budget you set.

How to use the position size calculator

  1. Enter your account size and the percentage you are willing to risk on this trade.
  2. Enter your intended entry price and your stop price.
  3. Add any per-trade fees so they come out of the risk budget rather than on top of it.
  4. Take the unit count as the maximum, never the minimum.

What people use this for

  • Sizing every trade to the same account risk regardless of the instrument.
  • Seeing why a wider stop must mean a smaller position.
  • Checking that a position is not too large a share of the account even when the risk is small.
  • Converting a risk rule into an order quantity before entering it.

Worked examples

Every figure below is produced by running this calculator against the example inputs, so the numbers always match the tool.

A one percent risk on a tight stop

$50,000 account, 1% risk, entry $42.50, stop $40.10.

Position size (units)
204
Risk budget
$500
Position as a share of the account
17.34%

The same risk with a wider stop

Identical account and risk, stop moved to $37.00.

Position size (units)
89
Position value
$3,783
Stop distance
12.94%

The stop decides the size

Two trades risking the same percentage of the account will have completely different position sizes if their stops are at different distances. That is correct behaviour, and it is the single most common thing newer traders get backwards.

Sizing by capital instead - a fixed dollar amount per trade, or a fixed number of shares - means the account risk changes on every trade without anyone choosing it.

Position value still matters

A very tight stop can produce a mathematically correct position that is an enormous share of the account. The risk is small if the stop holds, and the stop is exactly what fails during a gap or a halt.

That is why the position-as-a-percentage output exists alongside the risk figure. Many traders cap position value independently of the risk calculation for precisely this reason.

Rounding down, and fees

Units are rounded down so the risk never exceeds the budget. Fees are taken out of the budget rather than added on top, so the total loss at the stop stays within the amount you decided to risk.

On small accounts with high per-trade fees, this occasionally produces a position size of zero. That is a real answer - the trade cannot be taken at that risk level and that stop distance.

Methodology and assumptions

What this calculator does, and what it deliberately does not do.

  • Results are arithmetic on the numbers you enter. Nothing here predicts prices or connects to an exchange, broker or market data feed.
  • Nothing you type is transmitted or stored - the calculation runs entirely inside your browser.

This tool is for informational and educational purposes only and does not constitute financial or investment advice. Past performance does not guarantee future results.

Nothing on this website is a recommendation to buy, sell or hold any security, currency, derivative or digital asset. No price is predicted and no return is promised or implied.

Trading and investing carry the risk of substantial loss, including the loss of your entire capital. Leveraged products can produce losses that exceed your deposit. Tax treatment depends on your jurisdiction and your circumstances.

Frequently asked questions

What percentage should I risk per trade?

That is a personal decision this site will not make. The risk of ruin calculator shows what different levels do to survival probability, which is a more useful way to decide than a rule of thumb.

Does this work for contracts for difference or spread betting?

The unit arithmetic is the same. Leverage does not change the risk calculation, though it changes the margin required and introduces financing costs the calculation does not include.

Why did I get zero units?

Because the risk on a single unit, plus fees, exceeds the risk budget. Either the stop is too far away for this account size, or the risk percentage is too small for the fees involved.

Should I include fees?

Yes, if you want the loss at the stop to stay inside the intended risk. On frequently traded small positions, fees are a significant share of the budget.

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