Position Size Calculator

Why Position Sizing Matters More Than Stock Selection

Most traders obsess over which stock to buy. Very few think about how much to buy. That is the wrong priority. A great stock pick with an oversized position can wipe out your account. A mediocre trade with proper position sizing becomes a small, forgettable loss.

Position sizing is the mechanism that keeps you in the game long enough to be right. Even with a 60% win rate, you can blow up your account if you bet 50% of capital on a single trade that goes against you. The math is brutal and one-sided — losing 50% of your capital requires a 100% gain just to get back to even.

The principle behind every professional risk management system is the same: define the maximum amount you are willing to lose on any single trade before you enter. Everything else flows from that number.

The 1% to 2% Rule — Your Foundation

The standard approach used by most professional traders: never risk more than 1% to 2% of your total trading capital on a single trade. For a ₹10 lakh account, that means maximum risk per trade of ₹10,000 to ₹20,000.

Position size then follows directly from your stop loss:

Example: Capital = ₹10,00,000. Risk = 1% = ₹10,000. Stock entry at ₹500, stop loss at ₹480. Risk per share = ₹20.

Position Size = ₹10,000 ÷ ₹20 = 500 shares. Total investment = 500 × ₹500 = ₹2,50,000 (25% of capital deployed, but only 1% at risk).

This is the critical insight: you can deploy a large position while keeping your actual risk small, simply by placing your stop loss tightly. Conversely, a wide stop forces a smaller position to keep risk controlled.

Swing Trading vs. Intraday Position Sizing

Intraday traders typically use tighter stops (0.3% to 0.5% below entry) and can therefore take larger positions within the same risk budget. A swing trader holding for 5 to 15 days uses ATR-based stops that may be 2% to 5% wide, forcing smaller position sizes.

This is why intraday looks more exciting — larger share quantities, bigger nominal P&L swings. But the percentage risk is often identical to a swing trader's position if both are applying the 1-2% rule properly.

Kelly Criterion — A Reality Check on Aggressive Sizing

The Kelly Criterion gives you the theoretically optimal bet size to maximize long-term growth. The formula: Kelly % = W − [(1 − W) ÷ R], where W = win rate and R = average win ÷ average loss.

For a system with 50% win rate and 1.5:1 reward-to-risk ratio: Kelly = 0.50 − (0.50 ÷ 1.5) = 0.50 − 0.33 = 17%. That means 17% of capital per trade at full Kelly.

In practice, nobody uses full Kelly because the drawdowns are extreme. Half-Kelly (8.5% in this example) is the practical version. Even that is aggressive for most retail traders. The 1-2% rule is roughly one-tenth to one-fifth of Kelly, providing a large margin of safety for real-world conditions where your estimated win rate and payoff ratio are themselves uncertain.

The lesson from Kelly: position sizing is a function of your edge. More edge justifies larger positions. If you have no proven edge — and most new traders do not — stick to 0.5% risk per trade until you build one.

Concentration Risk and Portfolio Position Limits

Beyond per-trade risk, manage sector and theme concentration. If you have 5 open trades all in banking stocks, a negative RBI announcement hits all 5 at once. Your total portfolio drawdown in a single session can exceed 10% even with 2% risk per trade.

Professional practice: max 20% of capital in one sector, max 5-6 open positions at any time for a ₹10-25 lakh account. Larger accounts can run more positions but correlation management becomes critical.

F&O traders have an additional wrinkle: option buying requires margin (premium), but selling requires much larger SPAN + exposure margins. Your position sizing model must account for capital actually blocked versus risk actually taken. A ₹1.5 lakh margin block for selling a Nifty spread might only have ₹15,000 of actual risk — those are very different numbers.