Finance Position size calculator
Size a trade from the loss you can afford rather than the cash you happen to have. Enter your capital, your risk per trade and your stop, and get the quantity, the money at risk and the reward to risk ratio.
The whole account, not the amount you plan to put into this trade.
The share of the account you accept losing if the stop is hit. Most rules sit at 1% to 2%.
Where the idea is wrong. Put it where the chart says, then let it set the size.
Optional. It gives you the reward side of the ratio.
The most one name may take of the account, however tight the stop is.
Brokerage as a percentage of each transaction, counted on both legs.
Position size
62 shares
A position worth $2,976.00.
At risk
$248.00
0.99% of the account if the stop is hit.
- Risk budget
- $250.00
- Risk per share
- $4.00
- Stop distance
- 8.33%
- Position value
- $2,976.00
- Share of account
- 11.9%
- Reward at target
- $744.00
- Reward to risk
- 3.00 : 1
- Break even win rate
- 25%
- Target distance
- 25.00%
At 3.00 to 1, you need to be right 25% of the time just to stand still, before fees and slippage.
The same trade at other risk settings
One number decides everything else here. This is what changing it does to the same entry and the same stop.
| Risk | Size | Loss if stopped | After 5 straight losses |
|---|---|---|---|
| 0.5% | 31 shares | $124.00 | $24,381.22 |
| 1.0% | 62 shares | $248.00 | $23,774.75 |
| 2.0% | 125 shares | $500.00 | $22,598.02 |
| 3.0% | 130 shares | $520.00 | $21,468.35 |
| 5.0% | 130 shares | $520.00 | $19,344.52 |
What a losing streak costs
Losses compound the same way gains do. Each one is a percentage of what is left, and the gain needed to undo it grows faster than the loss itself.
| Losses in a row | Capital left | Down | Gain needed to recover |
|---|---|---|---|
| 1 | $24,750.00 | 1.0% | 1.0% |
| 3 | $24,257.48 | 3.0% | 3.1% |
| 5 | $23,774.75 | 4.9% | 5.2% |
| 10 | $22,609.55 | 9.6% | 10.6% |
Position sizing is the part of trading you control completely. You cannot make a stock go up, but you can decide in advance what being wrong costs you, and that single decision is what keeps a bad run from ending the account.
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Reembun. (2026, August 1). Position size calculator. https://reembun.com/position-size-calculator
How to use it
Enter the account and the risk
Trading capital is the whole account, not the amount you plan to put into this trade. Risk per trade is the share of it you accept losing, usually 1% to 2%.
Set the entry and the stop
The stop goes where the chart says the idea is wrong. The distance between the two prices is what decides the size.
Add a target and a ceiling
Target price gives you the reward to risk ratio. Position ceiling caps how much of the account a single name may take.
Read the size and the consequences
Position size, the cash at risk and the break even win rate are shown together, with the same trade at other risk settings underneath.
Size the trade from the loss, not the cash
Most people decide how much to buy from what is in the account. Position sizing reverses that: decide what being wrong costs, and let it determine the quantity.
risk budget = capital × risk per trade
loss per share = entry − stop (plus fees on both legs)
position size = risk budget ÷ loss per shareOn a $25,000 account risking 1% a trade, buying at $48 with a stop at $44:
- Risk budget: $250
- Loss per share: $4.00
- Position: 62 shares, worth $2,976
- Actually at risk: $248, or 0.99% of the account
The position is 11.9% of the account and the risk is 1% of it. Those are different numbers, and confusing them is what makes people think a 1% rule means buying $250 of stock.
Why the stop has to come first
The three inputs are not equal. The stop belongs to the chart or the thesis: it marks the price at which the reason for the trade no longer holds. The risk percentage belongs to your account and should barely change. The quantity is the only one that is derived, and it is the one most people fix first.
Setting the quantity first and then placing the stop wherever the loss feels tolerable produces a stop with no meaning, and a stop with no meaning gets hit by ordinary noise. The order matters more than the arithmetic.
What the risk percentage really controls
It controls survival, which does not show up on any single trade.
| Risk per trade | After 5 losses | After 10 losses | Gain needed to recover |
|---|---|---|---|
| 1% | down 4.9% | down 9.6% | 10.6% |
| 2% | down 9.6% | down 18.3% | 22.4% |
| 5% | down 22.6% | down 40.1% | 67.0% |
| 10% | down 41.0% | down 65.1% | 186.8% |
The last column is the one that decides it. Losses and recoveries are not symmetric: down 50% needs 100% back, down 65% needs 187%. Ten losses in a row is not a freak event over a few hundred trades, and the difference between a system that survives it and one that does not is a single input on this page.
Reward to risk, and the win rate it demands
A stop tells you what a losing trade costs. A target tells you what a winning one pays. The ratio between them sets the win rate you need simply to stand still:
break even win rate = risk ÷ (risk + reward)| Reward to risk | Break even win rate |
|---|---|
| 1 : 1 | 50% |
| 1.5 : 1 | 40% |
| 2 : 1 | 33% |
| 3 : 1 | 25% |
| 5 : 1 | 17% |
Neither number means anything alone. A strategy that is right 70% of the time at 1:2 loses money; one right 30% of the time at 1:4 makes it. Every figure above ignores fees and slippage, so treat the real bar as a few points higher than the table says.
The ceiling on one position
A very tight stop produces a very large position. Entry $48 with a stop at $47.75 risks 25 cents a share, and a $250 budget sizes that at 1,000 shares, or $48,000, which is nearly twice the account.
That is why the calculator carries a ceiling on any single holding, set at 25% by default. When the ceiling binds, the position is smaller than the risk budget alone would allow and less than the full budget is at stake. A tight stop is not a licence to hold most of your capital in one name, because gaps ignore stops: a stock that closes at $48 and opens at $41 on an earnings miss fills your stop at $41, not $47.75.
What this calculation cannot promise
Your stop will not always fill at your price. Gaps, halts and thin order books all move the fill against you. The loss figure here is the intended loss, not a guaranteed one.
Position sizing does not create an edge. It stops a bad run from ending the account, which is a precondition for an edge to show up, not a substitute for having one. Sized perfectly, a strategy with negative expectancy still goes to zero, only more slowly.
Risk of ruin is not risk of one trade. Correlated positions fail together. Five separate 1% trades in the same sector during the same news cycle are closer to one 5% trade than to five independent ones.
If you are adding to a position that has already fallen, size the addition as though it were a new trade and check the combined holding with the average down calculator before committing. This page is arithmetic for managing risk, not advice on which stock to buy or when.
Common questions
How do you calculate position size?
Divide the money you are willing to lose by the loss per share. On a $25,000 account risking 1%, the budget is $250. Buying at $48 with a stop at $44 risks $4 a share, so the position is 250 ÷ 4 = 62 shares, worth $2,976. The account size sets the risk; the stop distance sets the quantity.
How much should I risk per trade?
Most published trading rules land between 1% and 2% of capital per trade, and the reason is arithmetic rather than tradition. At 2%, ten consecutive losses cost 18% of the account and need 22% to recover. At 10% the same run costs 65% and needs 187% to recover. Small enough that a bad streak is survivable is the whole requirement.
Where should the stop loss go?
At the price that proves the idea wrong, which is a question about the chart or the thesis, never about the amount you want to lose. Set it there first and let it determine the quantity. Moving a stop closer to make a bigger position fit is the most common way this calculation gets used backwards.
What is a good reward to risk ratio?
Anything above 1 to 1 can work with a high enough win rate, and the two numbers only mean something together. At 2 to 1 you need to be right 33% of the time to break even; at 3 to 1, 25%; at 1 to 1, 50%. The calculator shows the break even win rate for your ratio so you can compare it with how often you are actually right.
Why is my position capped below the risk budget?
Because a tight stop can size a position into most of the account. The ceiling limits any single holding to a share of capital you set, so a stop half a percent below entry cannot quietly become an 80% position. When the ceiling binds, the amount at risk is lower than your budget and the calculator says so.
Does it account for brokerage fees?
Yes, on both legs. Fees widen the real loss per share, because you pay to enter and pay again when the stop is hit. On markets with a percentage commission this shrinks the position by a few percent, which matters at the edges where the size is close to a whole lot.
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