Type in four numbers: account size, the percent you’re willing to risk, your entry, and your stop. The calculator returns the exact number of shares that keeps a stopped-out trade at your planned dollar loss, plus the total position value so you can see whether the trade even fits your account. Share size is an output of your risk. It’s never a guess, and it’s never “whatever buying power allows.”
Everything runs in your browser. No signup, nothing stored.
How to use it
- Account size. The capital in your trading account, not your net worth. If you trade a $10,000 account out of a $200,000 portfolio, the input is $10,000.
- Risk per trade. The percent of the account you lose if the stop hits. The convention across trading literature is 1–2%; while you’re still figuring out whether your setups work, stay at the low end or below it. The calculator shows the dollar figure so you can react to it ($300 on a $15,000 account reads differently than “2%”).
- Entry and stop. Both come from the chart: a key level, the low of the pullback, below VWAP, wherever your setup says the trade is wrong. Set the stop first, then let the calculator hand you the share count. Doing it in the other order, picking a share count and backing into a stop that “fits,” is how a level becomes a wish. For thin names, add a slippage cushion (more on that below).
A worked long example
You trade a $20,000 account and risk 1% per trade, so $200. A gapper sets up with an entry at $14.50 and a logical stop at $14.10 under the premarket level.
Risk per share: $14.50 minus $14.10 = $0.40. Shares: $200 divided by $0.40 = 500 shares. Position value: 500 × $14.50 = $7,250, about 36% of the account. If the stop hits and you get a clean fill, you’re down $200. One trade, one R, planned in advance.
And a short
Same account, same $200 budget. You’re shorting into a failed bounce at $8.20 with a stop above the reclaim level at $8.50. Risk per share is $8.50 minus $8.20 = $0.30, so $200 ÷ $0.30 = 666 shares (the calculator rounds down; rounding up would overshoot your budget). Position value is roughly $5,460. The math is identical for shorts; only the direction of the stop flips.
The formula
Shares = (account size × risk percent) ÷ (distance from entry to stop)
That’s the fixed-fraction model, and the idea underneath it matters more than the arithmetic: your dollar risk stays constant while the share count floats with the stop distance. A 10-cent stop on the $14.50 example would have given you 2,000 shares; the $0.40 stop gave you 500. Either way, a losing trade costs $200. Tight stops buy you size, wide stops cost you size, and neither changes what a loss does to the account.
That constancy is the point. A string of five losers at fixed 1% is a 5% drawdown and a normal week. Five losers sized by feel, with one of them at 10x your usual risk, is how accounts blow up. If risk-per-trade and stop placement are new concepts, the guide to starting day trading covers where they fit in the overall process.
Check the position against your buying power
The formula has a blind spot: it doesn’t know what your broker will let you hold. Tight stops on expensive stocks produce big positions. A $5,000 account risking 1% ($50) with a 25-cent stop on a $62 large cap calculates out to 200 shares, a $12,400 position. That’s 2.5 times the account. Whether you can take it depends on the intraday buying power your broker extends, which since the elimination of the pattern day trader rule is governed by intraday margin requirements. Run your account through the intraday margin calculator to see what actually fits.
When the calculated position is bigger than your buying power, you have three honest options. Take a setup where the stop is a larger fraction of the price (the share count and position value both shrink). Trade a cheaper name with the same stop structure. Or cap the shares at what buying power allows and accept that you’re risking less than budget on this one. What you don’t do is move the stop closer to make the numbers work; that stop no longer means anything on the chart.
Thin stocks: pad the stop distance
A stop order becomes a market order once price touches the stop, and per the SEC’s stop order definition, the fill can differ from the stop price, especially in a fast market. On a thick large cap that difference is usually noise. On a low-float momentum name that’s flushing, it’s not.
Say you’re long that $6.40 gapper with a stop at $6.20: a planned $0.20 risk per share. The stock flushes through the level and your market order fills at $6.08. Actual risk: $0.32 per share, 60% over plan. If you sized 1,000 shares for a $200 loss, you just took $320.
The cushion field exists for exactly this. Add an estimate of the slippage you’d eat on a bad exit (a nickel or a dime on most thin names; more on true garbage) and the calculator sizes against the padded distance: $200 ÷ ($0.20 + $0.10) = 666 shares instead of 1,000. You give up size on the way in to keep the loss honest on the way out. On liquid names, leave it at zero.
One more reality check while we’re here. Most day traders lose money; the success-rate statistics are grim reading. Fixed-fraction sizing won’t turn a losing strategy into a winning one, but it does guarantee that no single trade decides the outcome, and that’s the version of you that’s still around in six months to improve.
Make it part of the routine
Sizing is half of trade planning; the payoff is the other half. Before you take the trade, run the same entry, stop, and target through the risk-reward calculator and confirm the setup pays at least two-to-one. After the trade, log the planned risk next to the actual fill. The gap between those two numbers is your slippage data, and it tells you what cushion to use next time. If you don’t keep a journal yet, the free trading journal template has columns for exactly this, and it’s the single download we’d push on anyone trading real money.
FAQ
How many shares should I buy per trade?
Divide your dollar risk (account size × risk percent) by the distance between your entry and your stop. A $20,000 account risking 1% with a 40-cent stop gets 500 shares. The share count changes trade to trade; the dollar risk doesn’t.
What percent of my account should I risk on one trade?
The convention in trading literature is 1–2% per trade, and the low end is the better default. At 1%, ten straight losers cost you about 10% of the account, which is survivable. While you’re still testing whether a strategy works at all, 0.5% or a simulator is the smarter lab.
Does the calculator work for short positions?
Yes. Enter the short entry and a stop above it; the calculator detects the direction and uses stop minus entry as the risk per share. The sizing math is identical to the long side.
What if the calculated position costs more than I have in the account?
That happens whenever the stop is tight relative to the share price, and it means the trade needs intraday margin. Check the position value against the buying power your broker extends under current intraday margin requirements, and if it doesn’t fit, take fewer shares or a setup with a wider stop relative to price. Never tighten the stop just to afford more size.
Why was my actual loss bigger than my planned risk?
Usually slippage: a stop order converts to a market order when triggered, and in a fast-moving or thinly traded stock the fill lands below your stop price (above it, on a short). Gaps through your level do the same thing. Pad the risk-per-share with the slippage cushion field when you trade thin names, and compare planned versus actual losses in your journal to calibrate it.