Position Sizing Made Simple

Ravi had Rs 2,00,000 in his trading account and a tip he liked. The stock was around Rs 100, so he bought 1,000 shares - a clean, round number that felt right. That was Rs 1,00,000, half his account, in one position, and he never once thought of it as half his account. He thought of it as "1,000 shares". A week later the stock slipped to Rs 85. His nice round number was now a Rs 15,000 hole - more than seven percent of everything he had, gone on a single trade he had sized by gut. He picked the quantity first and discovered the risk afterwards. Good position sizing does it the other way around.

How many shares should you buy? It is the most important question in trading, and almost no beginner asks it properly. They size by what feels normal: a round number, a tip's confidence, or how much cash is lying free. None of that has anything to do with risk. This chapter gives you one simple method that decides your quantity from your risk, so every trade puts roughly the same small slice of your capital on the line - whether the stock is Rs 50 or Rs 5,000.

Size is the risk you actually control

You cannot control whether a trade wins. You cannot control how far it runs or how fast it falls. The one thing fully in your hands before you click buy is how big the position is. Size decides how much a wrong trade costs. A brilliant idea in too large a size can end your account; a mediocre idea in a small size is survivable. That is why serious traders obsess over sizing far more than over entries. Get the size right and a losing streak is a flesh wound. Get it wrong and one bad week is fatal.

The one method, four steps

There is a single method worth learning, and it is just four steps.

1. Decide your risk per trade as a percent of capital. A common beginner choice is 1%. On Rs 2,00,000 that caps what you are willing to lose on one trade.
2. Turn it into rupees. 1% of Rs 2,00,000 = Rs 2,000. This is your rupee risk - the most this trade should cost you if your stop is hit.
3. Find your stop distance. Decide, before entering, the price where you will admit you are wrong and exit. Entry minus stop is the distance per share. Buy at Rs 100, stop at Rs 92, and the distance is Rs 8 per share.
4. Divide. Quantity = rupee risk / stop distance = Rs 2,000 / Rs 8 = 250 shares.

That is the whole method. Notice the price of the stock never set your size. Your risk did.

Wider stop, smaller size - not a bigger loss

Beginners think a wider stop means a bigger loss. It does not, if you size correctly. Your rupee risk stays fixed at Rs 2,000. A wider stop just means you divide that same Rs 2,000 by a bigger number, so you buy fewer shares. A tight Rs 4 stop buys 500 shares; an Rs 8 stop buys 250; a Rs 16 stop buys only 125. All three lose exactly Rs 2,000 if the stop is hit. The position shrinks to keep the loss the same. This is the insight most beginners miss: the stop distance changes how much you buy, not how much you lose.

Fixed-rupee versus percentage risk

There are two honest ways to set the rupee risk in step one.

• Fixed-rupee risk: you simply decide "I will risk Rs 2,000 per trade", full stop, regardless of how the account is doing. Steady and easy for a beginner. Its weakness is that it does not shrink when you are losing or grow when you are winning.
• Percentage risk: you risk a fixed percent (say 1%) of your current capital. As the account grows the rupee risk grows; as it shrinks the risk shrinks automatically. This is gentler on a losing streak - a smaller account makes smaller bets, which is exactly when you need the protection.

Both are fine. Many beginners start with fixed-rupee for simplicity and move to percentage once they are comfortable. Either way, keep the number small. One percent is a sober, common choice; 2% is already aggressive for a beginner.

The beginner calculator

The table below does the same arithmetic across different risk percents and stop distances, all on the same Rs 2,00,000 account. Read across a row and a wider stop buys fewer shares. Read down a column and a bigger risk budget buys more. In every cell the amount you actually risk is just the row's rupee risk.

How sizing differs by who you are

The same idea - risk a small, fixed amount - shows up differently depending on what you trade.

The F&O row is the one that trips beginners. Suppose the NIFTY lot is around 65 (lot sizes are revised periodically by the exchange - always check the current contract specs) and your stop on a futures trade is 30 points away. One lot risks 65 x 30 = Rs 1,950 - just inside a Rs 2,000 budget, so a single lot fits, with almost no room to spare. You cannot buy three-quarters of a lot, so if a wider stop or a larger lot pushed the risk past Rs 2,000, the trade would no longer fit and you would need a tighter stop or more capital. The method still rules; it just rounds to whole lots.

When this fails

The method assumes you actually exit at your stop for the loss you planned. Sometimes you do not. Price can gap - jump straight past your stop while the market is shut or in a fast move - so you exit far below Rs 92, maybe at Rs 80, losing Rs 20 a share instead of Rs 8. Your tidy "Rs 2,000 risk" becomes Rs 5,000. Results days, RBI policy, election results and global shocks all cause gaps. Position sizing controls your planned loss, not your worst-case loss. That is why even perfectly sized traders keep total exposure modest, avoid huge bets into known events, and never treat a stop as a guarantee. Sizing makes the normal losses survivable; it cannot make the rare ones vanish.

None of this is personalised advice. The 1% figure and the rupee amounts here are teaching examples, not a recommendation for your account. Pick numbers that fit your own capital and comfort, and treat sizing as a habit you repeat on every single trade, not a one-off calculation.

Quick self-check