Position Sizing Formula: How Many Shares to Buy, With Rupee Examples

The position sizing formula settles one question before every trade: how many shares should I buy? Most beginners pick a round number, or just put in whatever cash happens to be free. Professionals work backwards from how much they’re prepared to lose. That single change protects a trading account better than any indicator will.

Below you’ll find the core formula, worked examples in rupees, versions for F&O and for volatile stocks, and the mistakes that quietly wreck accounts.

In this article

1. The Position Sizing Formula
2. Worked Example 1: A Cash Market Trade
3. Worked Example 2: Same Capital, Wider Stop
4. Why Fixed-Fractional Sizing Works
5. Choosing Your Risk Per Trade
6. Position Sizing Formula for F&O
7. Volatility-Based Sizing With ATR
8. Other Position Sizing Methods Compared
9. Check Your Margin and Concentration Limits
10. Include Costs and Slippage
11. Common Position Sizing Mistakes
12. A Simple Pre-Trade Routine
13. Position Sizing and Your Edge
14. Frequently Asked Questions
15. Key Takeaways

The Position Sizing Formula

The standard fixed-fractional formula looks like this:

Position size (shares) = (Account capital × Risk per trade %) ÷ (Entry price − Stop-loss price)

There are three inputs:

• Account capital: the money sitting in your trading account, not your total savings.
• Risk per trade %: the share of capital you’re willing to lose if the stop gets hit. Many traders use 0.5% to 2%.
• Risk per share: the gap between your entry and your stop loss.

The top half of the formula is your rupee risk. The bottom half is your per-share risk. Divide one by the other and out comes the share count.

Worked Example 1: A Cash Market Trade

All the numbers below are illustrations, not real prices.

• Capital: ₹5,00,000
• Risk per trade: 1%, so rupee risk = ₹5,000
• Entry: ₹820
• Stop loss: ₹795
• Risk per share: ₹820 − ₹795 = ₹25

Position size = ₹5,000 ÷ ₹25 = 200 shares.

Position value = 200 × ₹820 = ₹1,64,000, or about 33% of capital. If the stop is hit, you lose ₹5,000, which is exactly 1%, before costs.

See how the position value is far bigger than the risk? Position sizing is about the loss, not about the amount you put in.

Worked Example 2: Same Capital, Wider Stop

Now suppose the chart tells you the right stop is ₹760, under a stronger support level.

• Risk per share: ₹820 − ₹760 = ₹60
• Position size = ₹5,000 ÷ ₹60 = 83.3, round down to 83 shares

The wider stop forces a smaller position, while your rupee risk stays exactly where it was. That’s the whole idea of the method: the stop decides the size, not the other way around.

Always round down. Rounding up nudges your risk higher without you noticing.

Why Fixed-Fractional Sizing Works

It survives losing streaks

Even a good strategy can lose ten trades in a row. At 1% risk per trade, ten straight losses cost about 9.6% of capital, because each loss is 1% of a slightly smaller account. At 10% per trade, the same streak would wipe out about 65%.

Recovery is asymmetric

A 10% loss needs an 11.1% gain just to get back to where you were. A 50% loss needs a 100% gain. Keeping losses small and controlled keeps you in the zone where recovery is actually realistic.

It scales automatically

As the account grows, 1% becomes a bigger rupee amount, so your positions grow with it. After losses, they shrink. You end up pressing when you’re winning and pulling back when you’re losing, without having to think about it.

Choosing Your Risk Per Trade

There isn’t one right number. A few things to weigh:

• Experience: beginners should stay at 0.5% to 1% while they prove their method works.
• Strategy win rate: strategies with lower win rates face longer losing streaks and need smaller risk.
• Correlation: five bank stocks are pretty much one big trade. Add up their combined risk.
• Total open risk: many traders cap total risk across all open positions at 5% to 6% of capital.

Our pillar guide on risk management in trading shows how these limits fit together.

Position Sizing Formula for F&O

Futures and options trade in fixed lots set by the exchange, so here you size in lots rather than shares.

Lots = Rupee risk ÷ (Risk per unit × Lot size)

Illustration: rupee risk of ₹5,000, a futures contract with a lot size of 75 units, and a stop 40 points away.

• Risk per lot = 40 × 75 = ₹3,000
• Lots = ₹5,000 ÷ ₹3,000 = 1.67, round down to 1 lot

If the answer comes out below 1, the trade is too big for your account at that stop. Skip it, or use a smaller instrument. Check current lot sizes on the NSE contract specifications page, since exchanges revise them from time to time.

When you buy options, your maximum loss is the premium you paid. Some traders size by premium: rupee risk ÷ (premium × lot size). Others still put a stop on the premium. Either way, write it down before you enter. Our options trading for beginners in India guide covers the basics.

Volatility-Based Sizing With ATR

A fixed rupee stop can be too tight for a jumpy stock and too loose for a calm one. That’s why many traders set stops with the Average True Range (ATR), which measures how much a stock typically moves in a day.

Stop distance = ATR × multiple (often 1.5 to 3)

Position size = Rupee risk ÷ (ATR × multiple)

Illustration: ATR of ₹18 and a multiple of 2, so the stop sits ₹36 away. With ₹5,000 of rupee risk, size = 138 shares.

What this does: volatile stocks get smaller positions and calm stocks get bigger ones, so each trade carries roughly the same risk.

Other Position Sizing Methods Compared

Fixed rupee amount

Some traders put the same sum, say ₹50,000, into every trade. Simple, yes, but the risk swings wildly. A trade with a 2% stop risks ₹1,000; one with a 10% stop risks ₹5,000.

Fixed number of shares

Buying 100 shares every time ignores price and volatility altogether. 100 shares of a ₹200 stock and 100 shares of a ₹5,000 stock are completely different bets.

Percentage of capital invested

Putting 10% of capital into each trade is better, but it still ignores where the stop is. Two trades of the same size can carry very different risk.

Kelly criterion

The Kelly formula sizes bets from the win rate and the payoff ratio. On paper it maximises long-run growth. In practice it throws up large, volatile positions, and win-rate estimates are rarely reliable. Traders who do use it often apply only a fraction, such as half-Kelly.

For most retail traders, fixed-fractional sizing built around the stop strikes the best balance between simplicity and control.

Check Your Margin and Concentration Limits

Sometimes the formula hands you a position bigger than you can afford, or one that’s too concentrated.

• Cash limit: a very tight stop can produce a huge share count. If the position value is more than your capital, cap it.
• Concentration cap: many traders limit any single position to 20% to 25% of capital, whatever the formula says.
• Liquidity: make sure the stock trades enough volume that your order won’t move the price.

Go with the smallest of the three: the formula result, the cash limit and the concentration cap.

Include Costs and Slippage

Real losses come out a little bigger than the formula suggests. Brokerage, STT, exchange charges, GST and stamp duty all add up. In a fast market or a gap down, stops can also fill below your level.

An easy fix is to add a small buffer to the per-share risk. For example, add ₹1 to ₹2 per share for liquid large caps, and more for smaller stocks.

Common Position Sizing Mistakes

• Sizing first, stop later. Choosing 500 shares and then putting the stop wherever it “fits” defeats the whole method.
• Moving the stop further away after entry, which pushes risk beyond the plan.
• Ignoring correlation. Three IT stocks bought on the same day is one sector bet.
• Raising risk after losses to “win it back.”
• Using total net worth as capital. Count only the money set aside for trading.
• Forgetting gap risk. Overnight news can open a stock well past your stop.

A Simple Pre-Trade Routine

1. Find the entry and the logical stop on the chart.
2. Work out rupee risk: capital × risk %.
3. Work out per-share risk, plus a cost buffer.
4. Divide and round down.
5. Check cash, concentration and total open risk limits.
6. Place the stop-loss order at the same time as the entry.

A spreadsheet with these six steps takes two minutes to build and takes the guesswork out of every trade.

Position Sizing and Your Edge

Sizing doesn’t create profits. What it does is protect capital, so a strategy with a real edge gets time to work. Pair it with a sensible risk-reward ratio and a tested entry method, like the setups in our position sizing and risk management article.

SEBI’s studies of individual F&O traders have found that most of them lose money (SEBI’s September 2024 study found that about 93% of individual equity F&O traders made net losses between FY22 and FY24). Strict sizing won’t guarantee profits, but it does limit how much any one mistake can cost you.

Frequently Asked Questions

What is the 1% rule in trading?

It means never risking more than 1% of your trading capital on a single trade. It’s about the possible loss, not the amount invested.

Should I recalculate size every trade?

Yes. Your capital and your stop distance change, so the share count should change too.

Does the formula work for long-term investing?

Investors usually size by conviction and portfolio weight rather than stop distance. The formula is built for trades with clearly defined exits.

Key Takeaways

The position sizing formula is simply rupee risk divided by per-share risk. Decide the stop first, keep your risk per trade small, round down, and stay within your cash and concentration limits.

This article is for education only and is not investment advice.