Position sizing is deciding how many shares or lots to trade, so that if the trade goes wrong, the loss is a small, planned fraction of your account instead of an accident. It is the quiet half of every trade decision. Most beginners obsess over what to buy and let quantity be whatever their available funds allow.
Why does quantity matter more than it looks?
Two traders can take the exact same trade (same stock, same entry, same stop-loss) and one gets a bruise while the other gets a broken leg. The only difference is size.
The danger of "buy as much as my funds allow" is that it ties your loss to your conviction, and conviction is highest exactly when you are about to be overconfident. Position sizing replaces that with a rule you set on a calm day and follow on a turbulent one.
How does the fixed-fraction convention work?
A common convention among traders is to risk only a small fixed fraction of the account on any one trade, often quoted as 1% to 2%. That is a convention many traders find useful, not a rule of the market or advice from Rupeezy; the fraction that suits you depends on your own capital and temperament.
Here is the method, step by step, with Arjun's numbers:
- Account size: Arjun has ₹1,00,000 in his trading account.
- Risk per trade: he follows the 1% convention, so the most one trade may cost him is ₹1,000.
- Stop distance: he wants to buy Kaveri Motors at ₹250 and has decided that if it falls to ₹240, his idea is wrong. His stop distance is ₹10 per share. (Placing that exit as an actual order is covered in what are stop-loss orders and how to use them?.)
- Quantity = risk per trade ÷ stop distance: ₹1,000 ÷ ₹10 = 100 shares.
If the stop-loss is hit, Arjun loses about ₹1,000, 1% of his account, exactly what he planned. Notice what the formula did: the stop decided the size. A wider stop forces a smaller position; a tighter stop allows a larger one. Risk stays constant either way.
| Stop distance | Risk per trade | Quantity |
|---|---|---|
| ₹5 | ₹1,000 | 200 shares |
| ₹10 | ₹1,000 | 100 shares |
| ₹25 | ₹1,000 | 40 shares |
What happens without position sizing?
Suppose Arjun had instead used his full ₹1,00,000 to buy 400 shares at ₹250. The same ₹10 fall now costs ₹4,000 (4% of his account) and a bad week with three such trades takes him down over 10%. With sizing, the same three losing trades cost about 3%. Same market, same mistakes, very different damage. And because deep losses need much larger gains to recover from, keeping each loss small is what makes losing streaks survivable. See what is a drawdown?.
Position sizing matters even more with borrowed exposure, because leverage magnifies both the position and the potential loss. See what is leverage and why is it risky?.
Things to keep in mind
- Size the position from your stop distance, not from how confident you feel or how much margin is available.
- The 1–2% figure is a common trader convention, not a prescription. Pick a fraction you could lose several times in a row without panic.
- Slippage and gaps mean a stop-loss can fill slightly beyond your stop price, so the actual loss can exceed the planned amount.
- Position sizing keeps losses survivable; it does not make any individual trade more likely to win.
Read next
What is the risk-reward ratio? — Size decides how much you can lose. This decides whether the trade is worth taking.