Free calculator
Position size calculator for stocks, margin, options and futures
Take the most you're OK losing and divide it by how much you could lose on each share or contract. That's your size.
For learning only. This does math on the numbers you enter, and it doesn't recommend any trade. Your numbers stay in your browser, and it rounds down to whole shares or contracts.
The math, step by step
Say you have $5,000, you're OK losing 1%, you'd buy a stock at $100 and you'd get out at $98. These are made-up numbers.
| Step | Math | Answer |
|---|---|---|
| Find your limit | 1% of $5,000 | $50 |
| Find your loss per share | $100 minus $98 | $2 |
| Divide | $50 ÷ $2 | 25 shares |
Notice what just happened. You didn't start by asking how many shares you want. You started with how much you can stand to lose.
How each market changes the math
Every example here uses made-up numbers and the same $5,000 account with a $50 limit.
Stocks and ETFs in a cash account
This is the math above. You only use your own money, so if your size costs more than you have, you buy fewer shares. On a stock you buy, the most you can lose is what you put in.
Stocks on margin
Margin lets you borrow, and it doesn't change your limit. Move your exit to $99.50 and the math says 100 shares, which costs $10,000. You'd put in $5,000 and borrow $5,000.
You could lose $50 at your exit. But if the stock kept falling and you stayed in, you'd lose your whole $5,000 at $50 a share, and below that you'd owe your broker money. At the usual 25% minimum, your broker can demand more money around $66.67, and many brokers require more. It can sell your stock with no warning.
Selling a stock short takes a margin account and your broker's approval. There's no ceiling on how high a stock can go, so there's no ceiling on the loss.
Buying options
One contract usually covers 100 shares, so a $1.50 option costs $150. If you'd sell at $1.00, you could lose $50 a contract, so the math says 1 contract.
But options can drop fast, and they can end worthless. If that one goes to zero, you lose $150, which is three times your limit. So the calculator shows you both numbers. To stay under $50 even if it goes to zero, that option doesn't fit your account.
This is only for buying calls and puts. Selling options can lose you far more, so leave that alone while you're learning.
Futures
You size by how many dollars each point is worth. One MES contract moves $5 for every point. If your exit is 8 points away, you could lose $40 a contract, so the math says 1 contract. If your exit has to be 15 points away, that's $75, so one contract is over your limit and you can skip the trade.
That small margin payment controls a lot of value. At a made-up price of 6,000, one MES contract is worth $30,000, on a $5,000 account. You can lose more than your whole account.
Try it with fake money
The math is the easy part. Doing it when you're mad is harder. Survive the Market gives you $10,000 in play money, and every chart is made up. If you raise your size right after a loss, the game calls it out. That's called a revenge trade.
Common questions
What percent should I risk per trade?
Lots of beginners risk about 1% of their account on a trade, or less. That's a common starting point, not a promise that you'll be safe. Losing streaks are normal, so pick a number you could survive several times in a row.
What if I can't afford the size it gives me?
Trade fewer. Don't borrow to make it work. A smaller size just means you could lose less than your limit. Here's how much money you need to start swing trading.
What if it says zero?
That means even one share or contract would put you over your limit. You can skip the trade. Skipping counts as a choice.
Can I really lose only what the calculator says?
No, that's not guaranteed. Prices can jump right past your exit, most often overnight or when a company reports earnings. Fees and the spread can add to the cost too. With margin, short selling and futures, you can lose more than you put in.
Should I use this for day trading on margin?
Enter the requirement your broker gives you, because day trading margin works differently. The $25,000 day trading rule was replaced on June 4, 2026, but brokers have until October 20, 2027 to switch, so ask yours which rules it uses.
Where should a beginner start?
Usually with big stocks and ETFs, using only their own money. That's a common starting point, not a recommendation. Save options and futures for after you've practiced, and read the risk papers first.