acalculator

What position size should I trade?

Type your account size, the percent you are willing to lose on one trade, your entry price and your stop-loss price. The position size calculator gives the number of shares, the money at risk, and what the position is worth; add a target price for the reward-to-risk ratio.

Your numbers

Many traders risk 1% or 2%.
Shares to trade
100

Trade 100 shares to risk $250.00 at a stop of $47.50.

Trade
Buy (long): the stop is below the entry
Money at risk
$250.00
Risk per share
$2.50
Position value
$5,000.00
Share of the account
20%
Loss at the stop
$250.00

Shares to trade: 100. Trade 100 shares to risk $250.00 at a stop of $47.50.

The results are estimates for information only. They are not financial, tax, or legal advice. Check the numbers with your lender or a qualified professional before you decide. Terms of use

How to calculate

Works out how many shares to buy or sell short so that a loss at your stop price is the share of your account you choose to risk, with the position value and the reward-to-risk ratio.

Example with the default inputs (Account size $25,000.00, Risk per trade 1%, Entry price $50.00, Stop-loss price $47.50): Trade 100 shares to risk $250.00 at a stop of $47.50.

Method: money at risk = account × risk% ÷ 100; risk per share = |entry − stop|; shares = ⌊money at risk ÷ risk per share⌋; position value = shares × entry; ratio = |target − entry| ÷ |entry − stop|.

  • The stop order fills at the stop price. A stop becomes a market order, so a fast market or a price gap can fill it lower (higher for a short) and lose more.
  • Commissions, fees and slippage are not included.
  • Shares are whole shares, rounded down so the loss at the stop is never above the money at risk.
  • This is a planning tool, not investment advice.

Machine-readable copies: Markdown, JSON.

Worked examples

Each example is checked against the calculator on every build.

  1. Account size $25,000.00, Risk per trade 1%, Entry price $50.00, Stop-loss price $47.50 gives Shares to trade 100, Money at risk $250.00, Risk per share $2.50, Position value $5,000.00, Share of the account 20%, Loss at the stop $250.00.Source: FINRA, Stop Orders: Factors to Consider During Volatile Markets (a stop order becomes a market order and may fill well past the stop price), https://www.finra.org/investors/insights/stop-orders-factors-consider-during-volatile-markets (retrieved 2026-10-03)
  2. Account size $10,000.00, Risk per trade 2%, Entry price $23.45, Stop-loss price $21.90, Target price $28.00 gives Shares to trade 129, Money at risk $200.00, Risk per share $1.55, Loss at the stop $199.95, Position value $3,025.05, Profit at the target $586.95, Reward-to-risk ratio 2.935484.Source: FINRA, Stop Orders: Factors to Consider During Volatile Markets (a stop order becomes a market order and may fill well past the stop price), https://www.finra.org/investors/insights/stop-orders-factors-consider-during-volatile-markets (retrieved 2026-10-03)
  3. Account size $50,000.00, Risk per trade 0.5%, Entry price $80.00, Stop-loss price $84.00, Target price $70.00 gives Shares to trade 62, Money at risk $250.00, Risk per share $4.00, Position value $4,960.00, Loss at the stop $248.00, Profit at the target $620.00, Reward-to-risk ratio 2.5.Source: FINRA, Stop Orders: Factors to Consider During Volatile Markets (a stop order becomes a market order and may fill well past the stop price), https://www.finra.org/investors/insights/stop-orders-factors-consider-during-volatile-markets (retrieved 2026-10-03)
  4. Account size $1,000.00, Risk per trade 1%, Entry price $0.30, Stop-loss price $0.10 gives Shares to trade 50, Money at risk $10.00, Risk per share $0.20, Position value $15.00.

How it works

The calculator works in exact decimals: every typed number is used as the decimal you typed, and only the share count is rounded.

  • Money at risk R = account × risk% ÷ 100.
  • Risk per share d = |entry − stop|. The stop must differ from the entry.
  • Shares n = ⌊R ÷ d⌋, the whole number of shares rounded down.
  • Position value = n × entry; share of the account = position value ÷ account × 100.
  • Loss at the stop = n × d, never above R.
  • Trade: a buy (long) when the stop is below the entry; a short sale when the stop is above it.
  • Target (optional): the gap to the target t = target − entry for a buy, entry − target for a short; it must be more than 0. Profit at the target = n × t and reward-to-risk ratio = t ÷ d.

Rules

  • Account from $1 to $10¹²; risk from 0.01% to 100%; entry from $0.0001 to $10⁷; stop and target from $0 to $10⁷.

Assumptions

  • The stop fills at exactly its price. A stop becomes a market order, so a gap can fill it worse.
  • Commissions, fees and slippage are not included. This is a planning tool, not investment advice.

Worked examples by hand

The default. R = 25,000 × 1 ÷ 100 = 250. d = 50 − 47.50 = 2.50. n = ⌊250 ÷ 2.50⌋ = 100 shares. Value = 100 × 50 = $5,000, 20% of the account; loss at the stop = $250.

$10,000 at 2%, entry $23.45, stop $21.90, target $28. R = 200, d = 1.55, 200 ÷ 1.55 = 129.03, so n = 129. Loss = 129 × 1.55 = $199.95; value = 129 × 23.45 = $3,025.05; t = 4.55, profit = $586.95; ratio = 4.55 ÷ 1.55 = 2.94.

A short: $50,000 at 0.5%, entry $80, stop $84, target $70. R = 250, d = 4, n = ⌊62.5⌋ = 62. Value = $4,960; loss = $248; t = 10, profit = $620; ratio = 2.5.

$1,000 at 1%, entry $0.30, stop $0.10. R = 10, d = 0.20, n = 50 exactly; value = $15.

Other questions people ask

How do I calculate position size?

Multiply the account by the risk percent to get the money at risk, then divide by the gap between the entry and the stop. With $25,000, 1% risk, an entry at $50 and a stop at $47.50: 250 ÷ 2.50 = 100 shares.

Why is the share count rounded down?

You can only trade whole shares here, and rounding up would make the loss at the stop larger than the risk you chose. $200 of risk at $1.55 a share is 129.03 shares, so the page says 129, which loses $199.95 at the stop.

Can I lose more than the money at risk?

Yes. A stop order becomes a market order when the stop price is reached, and FINRA warns it can fill well below the stop price in a fast market or after a price gap. Fees and commissions are not included either.

Does it work for short sales?

Yes. Put the stop above the entry price. The risk per share is still the gap between the two, and a target must be below the entry.

What does the reward-to-risk ratio mean?

It is the gap from the entry to the target divided by the gap from the entry to the stop. A ratio of 2 means the planned profit is twice the planned loss.

Why can the position be worth more than my account?

A tight stop gives a large share count. If the position value is over 100% of the account you would need margin, so many traders also cap the position size.