Position Size Calculator
Risk the Right Amount, Every Trade
Find your share size from account risk, entry, and stop — or work backward from a known position to find your stop and target.
Rec. ≤1% · Hard cap 2%
Why Position Sizing Is the Skill That Keeps You in the Game
The calculator exists because of a specific mistake I made. Early on, I took a trade with a $25 planned risk, the stock moved against me, and instead of taking the small loss I'd decided on, I froze and let it run — turning a $25 risk into a four-figure loss. The setup wasn't the problem. The size was, and so was not having the number in front of me before I clicked buy.
That's what position sizing is: deciding, before you enter, exactly how many shares to buy so that if the trade hits your stop, you lose only the amount you already agreed to lose. It's the difference between a business and a slot machine. You can be right less than half the time and still come out ahead — but only if every loss is small and controlled. Position sizing is what makes that true.
The Formula, in Plain Terms
Every share-size calculation is the same three steps, and the tool above just does them instantly:
Shares to buy = (Account × Risk %) ÷ (Entry price − Stop price)
Read it left to right. Account × Risk % is your dollar risk — the most you'll lose on this trade. On a $10,000 account risking 1%, that's $100. Entry − Stop is your risk per share — how far the price travels from your entry to your stop. If you buy at $1.50 with a stop at $1.35, that's $0.15 per share. Divide $100 by $0.15 and you get about 666 shares. Buy more than that and a stop-out costs you more than you decided to risk. That's the entire idea, and it never changes.
A Worked Example, Start to Finish
Say you have a $25,000 account and you're day trading, so you cap risk at 2% — $500. You spot an entry at $4.00 and your stop, based on the chart, sits at $3.80. Your risk per share is $0.20. Five hundred dollars divided by $0.20 is 2,500 shares, a $10,000 position. If the trade stops out, you lose $500 — exactly what you planned, no more. If your target was $4.60, you'd make $1,500: a 3-to-1 reward-to-risk trade. The calculator shows all of this the moment you type the numbers in.
How Much Should You Risk Per Trade?
Less than feels exciting. The calculator caps risk by trading style — roughly 1% for scalping, 2% for day trading, 3% for swing, 5% for position trades — because faster styles take more trades, and more trades means each one has to hurt less. These are ceilings, not targets; plenty of experienced traders risk well under 1%. If you're not sure which style you are, that choice comes first and it drives everything else — the types of trading guide walks through it. And if any term here is unfamiliar, the glossary defines it in plain English.
The Two Modes
Find Share Size is the everyday one: you know your entry and your stop, and you want the share count that keeps your risk where it belongs. Find Stop & Target works backwards — you already hold a position, or you know how many shares you want, and you need to see where your stop and target have to sit to make the math work. Most traders live in the first mode and reach for the second when they're planning around a position they already have.
Common Questions
What percentage should I risk per trade?
A common ceiling is 1–2% of your account per trade, and less is defensible. The point isn't the exact number — it's that a string of losses can't take you out. At 2% risk, ten losses in a row costs about 18% of your account. At 10% risk, the same streak nearly ends you. Small enough to survive a bad run is the whole target.
What does “R” mean?
R is your risk on a trade expressed as one unit. If you risk $100, then 1R is $100 — a winner that makes $300 is a 3R trade, a loss is −1R. Measuring in R instead of dollars lets you compare trades and account sizes on equal footing, and it's how I track my own results, because it shows consistency rather than just the size of the account.
Is position sizing the same as money management?
Position sizing is the biggest piece of money management, but not all of it. Sizing answers “how many shares on this trade.” Money management is the wider set of rules around it — how much of your account is ever at risk at once, when you stop trading for the day, how you scale after wins or losses. The calculator handles the sizing; the discipline is on you.
Why does the calculator need a stop price?
Because without a stop, there's no such thing as position sizing — there's just buying shares and hoping. The distance from your entry to your stop is what defines your risk per share, and that's half the formula. If you don't know where you're wrong before you enter, you can't size the trade, and honestly you're not ready to take it. Decide the stop first, always.
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