Most beginners ask – what stock they should buy, before figuring out how many shares to buy.
And often, the second question is the one that really decides whether you stay in the game – or end up getting wiped out.
Position sizing is the habit of answering that second question – how many shares to buy – with a hard-nosed calculation, rather than just going with a hunch.
What is Position Sizing?
Position sizing is deciding how much of your money, or how many shares, to put into each single trade.
It is all about figuring out how much of your capital you’re prepared to lose if the trade goes sour.
The key idea is that you figure out how much you’re willing to lose and fix that number, then let that number decide how big the trade needs to be.
And here is the thing – your confidence in the trade doesn’t come into it.
Why it Matters
It is possible for a strategy to be right more often than it is wrong. But still end up wiping out an account because one bad trade comes along at just the wrong time.
Position sizing is what keeps each loss small enough that you can ride it out.
It also helps with the emotions that come into play when you are trading.
When a trade is too big, it is easy to get spooked and bail out too early – and when you do lose, you are tempted to try and recoup your losses by chasing after the trade.
But a trade that is sized for a small, deliberate loss is a heck of a lot easier to just hold steady and wait it out.
The Position Sizing Formula
Quantity = (Capital × Risk %) ÷ (Entry Price − Stop-Loss Price)
- Capital: the total trading money you have
- Risk %: the share of capital you will risk on one trade
- Entry – Stop-Loss: the loss per share if your stop-loss is hit
Worked Example
Suppose you have ₹5,00,000 and decide to risk 1% per trade.
| Step | Calculation | Result |
| Maximum loss allowed | ₹5,00,000 × 1% | ₹5,000 |
| Entry price | ₹500 | |
| Stop-loss price | ₹480 | |
| Loss per share | ₹500 − ₹480 | ₹20 |
| Quantity to buy | ₹5,000 ÷ ₹20 | 250 shares |
| Position value | 250 × ₹500 | ₹1,25,000 |
Your position is ₹1,25,000, which is 25% of your capital.
Your risk is only ₹5,000, which is 1%.
Position size and risk are two different things.
How the Stop-Loss Changes Your Quantity
The stop-loss distance is the number that changes your quantity.
With the same ₹5,000 risk:
| Stop-Loss Distance | Quantity | Position Value (at ₹500) |
| ₹10 | 500 shares | ₹2,50,000 |
| ₹20 | 250 shares | ₹1,25,000 |
| ₹40 | 125 shares | ₹62,500 |
A wider stop-loss means a smaller position. A tighter one allows a larger position.
You never move the stop-loss closer just to buy more shares.
Choosing Your Risk Percentage
Many traders keep risk between 0.5% and 2% of capital per trade. This is a common guideline, not a rule set by SEBI or the exchanges.
The right number depends on your experience and how much loss you can handle comfortably.
| Risk per Trade | Loss on ₹5,00,000 | Capital left after 10 losses in a row (approx.) |
| 1% | ₹5,000 | About 90% |
| 5% | ₹25,000 | About 60% |
After a 40% drawdown, you need roughly a 67% gain just to get back to where you started.
Small risk per trade protects you from that hole.
Position Sizing in Futures and Options
When you’re trading futures or options, you’re working in fixed lot sizes – so your quantity is going to move in set amounts.
What you do is work out your quantity using the formula, then round it down to the nearest lot.
And if one lot looks like it’s going to risk more than you’re comfortable with, then either skip the trade or change up your setup.
Keep in mind that the exchanges do change up the lot sizes from time to time.
So you need to keep an eye on them before you do any calculations.
Common Mistakes
- Buying a “round number” of shares instead of calculating
- Using the same quantity for every stock, whatever its volatility
- Moving the stop-loss further away after entry, so the loss grows beyond your plan
- Increasing size after a winning streak or to recover a loss
- Ignoring brokerage, taxes and slippage, which add to your real loss
Tips for Better Position Sizing
- Decide your risk percentage before the market opens, not during a trade
- Calculate the quantity before you place the order
- Reduce size when the market is volatile
- Keep a trading journal to check whether your sizing stays consistent
- Practise on a demo account before using real money
Conclusion
Position sizing turns that second question – how many shares to buy – into a clear, straightforward calculation based on how much you are prepared to lose.
You figure out how much risk you’re happy to take on, measure the distance to your stop-loss, and then let the formula set the quantity.
And you can’t control whether a trade works out or not. But you can control how much it costs you when it doesn’t.
This lesson is for educational purposes only and is not investment advice.
