Position Size Calculator

1. Enter your trading account size (total equity you are sizing against).
2. Set risk per trade as a percent of that account (many traders stay near 1–2%; the slider allows 0.5–5% for illustration).
3. Enter the planned entry price for a long-style example.
4. Enter the stop-loss price below entry — the level where you exit if the trade fails.
5. Enter a take-profit price above entry so the tool can show reward and risk/reward ratio.

Risk amount is account size multiplied by your risk percent. Stop distance is the absolute difference between entry and stop. Position size in shares is risk amount divided by stop distance (floored to a whole share in this model). Reward assumes the same share count reaches your take-profit. Risk/reward compares take-profit distance to stop distance. The tool also shows total position value and what percent of the account that notional represents. Keeping risk percent fixed forces you to cut size when stops are wide and allows more size only when invalidation is close — the core idea behind percentage-based position sizing used in many discretionary and algorithmic playbooks.

Risk amount = Account size × (Risk % ÷ 100)
Shares = floor(Risk amount ÷ |Entry − Stop|)
Reward = Shares × |Take profit − Entry|
R:R = |Take profit − Entry| ÷ |Entry − Stop|

Take a $25,000 account risking 2% per trade, entering at $150, stopping at $142, and targeting $168. Risk amount = $25,000 × 0.02 = $500. Stop distance = $8, so shares = floor($500 ÷ $8) = 62. Position value ≈ 62 × $150 = $9,300 (~37% of the account notionally, while cash risk stays about $500 if the stop is respected). Take-profit distance = $18, so reward ≈ 62 × $18 = $1,116 and R:R ≈ 2.25. Compare that with the same prices at 1% risk: risk amount drops to $250 and shares fall to 31 — half the loss if stopped, with a smaller notional. Risking 5% for the same stop balloons share count and dollar loss if the stop hits. A second asset-style check: if entry were $50 and stop $47 (still a $3 risk per share) at 2% on $25,000, shares = floor($500 ÷ $3) = 166 — same dollar risk, different share count. Widen the stop without cutting size and you silently risk more than your intended percent — the most common sizing error.

Position size

How many shares (units) to buy so that a move from entry to stop loses about your chosen risk amount, assuming the stop fills at that price.

Risk amount

Dollars you plan to lose if the stop is hit: account size times risk percent.

Reward amount / Risk-reward ratio

Potential gain to the take-profit on the same size, and how that gain compares to the stop distance. Higher R:R is not automatically a good trade — edge and probability still matter.

Total position value / % of account

Notional exposure. You can risk 2% of equity while controlling a much larger notional if the stop is tight; watch leverage, margin, and concentration.

• Picking share count first and only checking risk afterward — which often oversizes the trade.
• Moving the stop farther away without reducing size, so dollar risk exceeds the intended percent.
• Using 5%+ risk per trade and calling it “aggressive” when it can compound into large drawdowns.
• Ignoring slippage and gaps: stops are not guaranteed fills at the stop price.
• Treating a favorable R:R as a reason to take a low-quality setup.

Long-oriented example with whole-share flooring, fixed dollar prices, and fills exactly at entry, stop, and take-profit. No commissions, slippage, borrow fees, overnight financing, or partial fills. Risk percent applies to the account size you enter, not buying power after other open positions or unsettled cash. Correlation across simultaneous trades is ignored — five “2% risk” ideas can still stack into a much larger portfolio shock. Results are for education and practice sizing — not a recommendation to buy or sell any security.

• SEC Investor.gov — Investment products and risks
• FINRA — Order types and how they work
• AlgoFinanceLab — Algorithmic trading guides

Dig deeper with our algorithmic trading for beginners guide, or try Robo Advisor Fee Comparison and Portfolio Rebalancer.

Estimates only — not financial, lending, or investment advice. Decisions should be based on your full situation and professional guidance where appropriate.