Position Size Calculator

Frequently Asked Questions

How does position sizing work?

Risk dollars = account equity × risk %. Shares = risk dollars ÷ (entry − stop). This caps the loss at your chosen percentage if the stop is hit.

What risk percentage should I use?

Many traders risk 0.5–2% of equity per trade. Smaller percentages survive longer losing streaks; the right level depends on strategy win rate and edge.

Why size by stop distance?

A wider stop needs fewer shares to keep the same dollar risk, and a tighter stop allows more. Sizing by stop keeps risk constant regardless of volatility.

Does this account for leverage?

It sizes by risk, not buying power. Always check the resulting position value against your available margin and concentration limits.

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Estimates only. Not investment advice.

Investment Disclaimer: Estimates only. Not investment advice.

This calculator provides estimates for educational purposes only and is not investment advice. Past performance does not guarantee future results. Consult with a qualified financial advisor before making investment decisions. All investments carry risk, including potential loss of principal.

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How This Calculator Works

Position sizing answers the only question that keeps a trading account alive: how many shares can I buy without risking more than I can afford on a single idea? The fixed-fractional method works in three steps. First, dollar risk = account size × risk percentage per trade. Second, risk per share = the absolute distance between your entry price and your stop-loss, |Entry − Stop|. Third, shares = dollar risk ÷ risk per share, rounded down so you never exceed the budget. The calculator also reports the resulting position value, what fraction of the account it represents, and the actual dollars at risk after rounding. The defining feature of this approach is that it sizes from the stop distance, not from a fixed dollar amount - a tight stop lets you hold more shares for the same risk, a wide stop fewer.

Worked Numeric Example

Account = $25,000, risk = 1% per trade, entry = $50, stop = $47. Dollar risk = 25,000 × 0.01 = $250. Risk per share = |50 − 47| = $3. Shares = 250 ÷ 3 = 83.33 → 83 shares (round down). Position value = 83 × $50 = $4,150, which is 16.6% of the account, while the true money at risk is only 83 × $3 = $249. If the stop were $49 instead, risk per share drops to $1 and you could hold 250 shares - same $250 risk, very different exposure.

Real-World Use

Professional traders and prop firms enforce a per-trade risk cap (commonly 0.5–2%) precisely so that a string of losers cannot blow up the account. The R-multiple framework builds on this: one "R" equals your dollar risk, so a trade that returns three times the risk is "+3R" regardless of the share count. Tracking results in R rather than dollars makes performance comparable across position sizes and is the backbone of most trading journals - a system with a modest 45% win rate is still highly profitable if its average winner is +2R and its average loser is −1R. Funded-account programs and prop-firm challenges typically fail a trader the moment cumulative risk breaches a fixed drawdown limit, so disciplined fixed-fractional sizing is not optional there; it is the survival constraint that decides whether the account exists tomorrow.

Common Mistakes

Sizing from a round share count instead of the stop distance - identical share counts carry wildly different risk.

Risking too large a fraction; at 5% per trade, ten consecutive losses cut the account roughly in half.

Ignoring slippage and gaps - a stop is a target, not a guarantee, especially on overnight or earnings moves.

Forgetting commissions, leverage limits, and that shorting has different margin and borrow constraints than going long.

Moving or widening the stop after entry "to give it room" - this silently increases real risk far beyond the planned 1R.

Limitations & Related Tools

This model assumes the stop fills at the stated price and ignores correlation between open positions - five "1% risk" trades in the same sector behave like one large 5% bet when that sector gaps against you, so total portfolio heat matters more than any single trade. It also assumes you can buy fractional-free whole shares and ignores margin interest, pattern-day-trader rules, and the reality that fast markets blow through stops. Combine it with a risk-of-ruin or Kelly criterion calculator to choose a sustainable risk fraction, a maximum-drawdown tool to stress-test a losing streak, and a volatility or ATR measure so the stop is placed at a structurally sensible distance rather than an arbitrary one. These figures are educational estimates, not trading or investment advice; trading carries a substantial risk of loss.

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