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Finance Calc Kit
Investments

Position Size Calculator

Calculate the optimal position size for your trades based on account balance, risk percentage, entry price, and stop loss.

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Position size

133 shares

Number of shares or units to buy

Total investment

$19,950.00

Capital required at entry

Risk amount

$1,000.00

2.0% of account balance

Potential loss

$997.50

Loss if stop loss is hit

Investment % of account

39.9%

Capital deployed relative to balance

Trade direction

Long (buy)

Inferred from entry vs stop loss

Stop loss distance

$7.50

Price move to stop loss

Risk amount vs total investment

Total investment$19,950.00
  • Risk amount$1,000.00
  • Total investment$19,950.00
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What is position sizing?

Position sizing determines how many shares or units to buy so that a losing trade costs no more than a fixed percentage of your account. It links account balance, risk tolerance, entry price, and stop loss into one share count. All math runs in your browser.

Pair position sizing with the maximum drawdown calculator to understand how consecutive losses affect portfolio value. For portfolio-level risk across multiple holdings, see the portfolio beta calculator. To compare potential profit against stop-loss risk before sizing, use the risk-reward ratio calculator. For momentum context at your entry level, check the relative strength index calculator.

Position size formulas

First, calculate the dollar amount you are willing to lose on the trade:

Risk Amount=Account Balance×Risk %100\text{Risk Amount} = \text{Account Balance} \times \frac{\text{Risk \%}}{100}

Next, find the per-share distance to your stop loss:

Stop Loss Distance=∣Entry Price−Stop Loss Price∣\text{Stop Loss Distance} = |\text{Entry Price} - \text{Stop Loss Price}|

Divide risk amount by stop loss distance and round down to whole shares:

Position Size=⌊Risk AmountStop Loss Distance⌋\text{Position Size} = \left\lfloor \frac{\text{Risk Amount}}{\text{Stop Loss Distance}} \right\rfloor

Worked example

A trader has a $50,000 account, risks 2% per trade, enters at $150, and sets a stop loss at $142.50.

  • Risk amount = $50,000 x 2% = $1,000
  • Stop loss distance = |$150.00 - $142.50| = $7.50
  • Position size = floor($1,000 / $7.50) = 133 shares
  • Total investment = 133 x $150 = $19,950
  • Potential loss = 133 x $7.50 = $997.50

The trade deploys 39.9% of the account but risks only 2%, because the stop loss limits downside per share.

Why position sizing matters

Without a fixed risk rule, traders often size positions by gut feel or available cash. A few large losses can erase months of gains. The 1% to 2% risk-per-trade rule, common among professional traders, keeps any single loss manageable and preserves capital for recovery.

Frequently asked questions

What is the 2% risk rule in trading?
The 2% rule means you risk no more than 2% of your account balance on any single trade. On a $50,000 account, maximum risk per trade is $1,000. Conservative traders often use 1% instead.
Why floor the position size to whole shares?
Most stock brokers require whole-share orders. Flooring ensures you never buy fractional shares beyond what your risk budget allows. The actual risk will be slightly less than your target when flooring reduces share count.
Does this work for short trades?
Yes. The calculator infers long or short direction from whether the entry price is above or below the stop loss. The same risk amount divided by stop loss distance formula applies to both directions.
What if my total investment exceeds my account balance?
The calculator shows investment as a percentage of account. If it exceeds 100%, you need more capital or a tighter stop loss. Margin can fund the gap, but that adds leverage risk beyond the stop loss amount.
How does position sizing relate to maximum drawdown?
Position sizing limits loss per trade. Maximum drawdown measures the worst peak-to-trough decline across many trades. Consistent 1% to 2% risk sizing helps keep maximum drawdown within tolerable bounds over time.

Resources and references

The formulas and methods in this calculator were checked against these independent sources.