Calculator
Position size calculator
Enter your account, the share you are willing to lose and your entry and stop. The calculator returns the number of units, the maximum planned loss and the size of the position.
Quick answer
Units = (account × risk %) / (entry - stop). With $10,000, 1% risk, entry $100 and stop $95 you trade 20 units, and the planned loss is $100. A stop can fill at a worse price than you set [1].
This calculator needs JavaScript. The formula and a worked example below show the same calculation by hand.
Key points
- Size comes from the loss you accept, not from how much you want to buy.
- The planned loss assumes your stop fills at its price; it may not [4].
- Check the position value against your account and any margin rules.
On this page
How does the calculator work?#
It applies one formula. First it multiplies your account by your risk percentage to get the amount at risk. Then it divides that amount by the distance between your entry and your stop, which is what one unit loses if the stop fills at its price.
units = (account × risk %) / |entry - stop|
It also shows the position value (units × entry) and what share of your account that value represents, because a small planned loss can still sit inside a very large position.
Can you check the result by hand?#
| Stop | Units | Position value |
|---|---|---|
| $98 | 50 | $5,000 |
| $95 | 20 | $2,000 |
| $90 | 10 | $1,000 |
What does the calculator not account for?#
- Gaps and slippage. When the stop price is reached, a stop order becomes a market order and can fill at a significantly different price [1].
- Costs. Spreads, commissions and financing are not included. Use the trading cost calculator for those.
- Leverage limits. Your broker's margin rules may stop you opening the full size. The CFTC notes that with a 2 percent margin requirement a $100,000 forex position needs $2,000 of margin [2].
- Lot sizes. Many brokers only accept whole units or set lot sizes, so round down.
How do you choose the risk percentage?#
The regulator guidance we cite gives no fixed figure. It does say to trade only risk capital, money beyond what you need for necessities, emergencies, savings and long-term goals [3]. A small, fixed percentage means a run of losses shrinks your account slowly instead of quickly. Read the full explanation in position sizing: decide the loss before the trade.
Frequently asked questions#
Why does a tighter stop give me more units?
Because the amount at risk stays fixed. If each unit can only lose $2 instead of $5, you can hold more units for the same planned loss. The position becomes larger, and a small price move can stop you out.
Does this work for crypto and forex?
The arithmetic is the same for any asset priced per unit. For forex, enter the price in the quote currency per unit of the base currency and the size in units, not lots.
Is the maximum loss guaranteed?
No. FINRA states that stop prices are not guaranteed execution prices [4]. The figure shown is the planned loss if the stop fills exactly at its price.
The bottom line#
Use the calculator before every trade, round the size down, and remember the planned loss is a plan, not a promise. For the reasoning behind the formula, read position sizing and the other risk management explainers.
Sources
Education only. This page is not investment, tax or legal advice. Trading and crypto can lose you money. See our risk disclosure.
