Most traders spend their time on entries. The entry decides whether a trade is interesting; the position size decides whether the trader survives being wrong. Two people can take the same setup, with the same stop and the same target, and have completely different outcomes because one risked 0.5% of capital and the other risked 5%.
Position sizing is the calculation that converts a price idea into a rupee risk. It is simple arithmetic, and it is the most frequently skipped step in retail trading. This guide explains the calculation, the difference between stop distance and risk, and the portfolio-level limits that prevent a series of ordinary losses from becoming an account-ending event.
The basic calculation
Start with three numbers: the capital you are trading, the maximum percentage you are willing to lose on one trade, and the distance between your entry and your stop. The position size follows from them.
Risk per trade = Capital × Risk %
Position size (shares) = Risk per trade ÷ Stop distance per share
Position value = Position size × Entry price
Suppose you have ₹2,00,000 and are willing to risk 1% per trade, which is ₹2,000. You want to buy a stock at ₹500 with a stop at ₹480, so the stop distance is ₹20 per share. The position size is ₹2,000 ÷ ₹20 = 100 shares. The position value is 100 × ₹500 = ₹50,000, which is 25% of your capital. If the stop is hit, you lose ₹2,000 plus costs, not the full ₹50,000.
Notice how the position size changes when the stop moves. If the stop is at ₹490, the distance is ₹10, and the size becomes 200 shares, worth ₹1,00,000. The risk is the same ₹2,000, but the exposure is larger. This is why a tighter stop is not automatically safer: it allows a bigger position, and a bigger position is more sensitive to slippage and gaps.
Risk percentage is a decision, not a default
The 1% figure is a common convention, not a law. A beginner with a small account and limited experience may be better served by 0.25% to 0.5% per trade while learning. A professional with a tested method, a long record and a separate income may use a higher figure, but the higher the risk per trade, the shorter the losing streak that can end the account.
| Risk per trade | Losses in a row to lose 25% of capital | What it implies |
|---|---|---|
| 0.5% | About 58 | Very conservative; slow to grow, hard to knock out. |
| 1% | About 29 | A common learning-to-intermediate setting. |
| 2% | About 14 | Manageable for a tested method, but a normal drawdown hurts. |
| 5% | About 6 | A short losing streak can force a strategy change. |
| 10% | About 3 | One bad week can end the account. |
The table assumes each loss is exactly the planned amount, which is optimistic. Slippage can make a loss larger, and a gap can make it much larger. Size as if the realised loss will be worse than the planned loss, especially in swing trading and derivatives.
Stop distance is not the same as volatility
A stop placed at an arbitrary 1% below entry ignores how much the instrument normally moves. If a stock routinely swings 3% a day, a 1% stop will be hit by noise before the idea has a chance. A better approach is to place the stop beyond a structural level and then check that the distance is consistent with the instrument’s normal range. Average true range (ATR) is one way to measure that range.
If the structural stop is too far away, the position size becomes small, and the trade may not be worth the effort. That is useful information: the setup does not offer enough edge at a risk you can afford. Skipping it is a decision, not a failure. The alternative, widening the position size to make the trade “worth it”, is how a controlled risk becomes an uncontrolled one.
Gaps and overnight risk
A stop loss is an instruction, not a guarantee. In swing trading, a stock can gap below your stop after results or news, and the realised loss can be several times the planned amount. Position sizing must account for that. One practical approach is to reduce size before known events, or to avoid holding a position through an event whose outcome you cannot assess.
In derivatives, the equivalent is mark-to-market and margin. A futures position can move against you overnight and trigger a margin call before you have a chance to act. The position size must be small enough that the worst plausible gap is survivable. If it is not, the trade is too large, regardless of how good the setup looks.
Portfolio-level risk
Five positions that all lose in the same market condition are not five independent risks. If you hold five banks and the sector sells off, you have one large bet, not five small ones. Correlation matters most in a crisis, when diversification is least reliable. A portfolio-level risk budget asks how much the whole book can lose in a bad scenario, not just how much each trade risks.
A simple starting rule is to cap total open risk across all positions at a multiple of the per-trade risk, for example 3% to 6% of capital. That means you cannot have ten positions each risking 1% at the same time. The cap forces you to prioritise the best setups and to notice when your positions are really the same trade.
A worked example with a gap
Suppose you buy 100 shares at ₹500 with a stop at ₹480, planning to risk ₹2,000. The company reports poor results after the close and the stock opens at ₹455 the next morning. The stop triggers near the open, and the realised loss is ₹4,500 plus costs, more than twice the planned amount. The position was sized correctly for a normal stop, but not for a gap.
The lesson is not that the calculation was wrong; it is that the calculation assumes the stop is honoured. Before holding a position through results, a budget or a major announcement, either reduce the size or accept that the worst case is larger than the planned risk. A simple stress test asks: if this stock gaps 10% against me tomorrow, what percentage of capital do I lose? If the answer is uncomfortable, the position is too large for an event.
Scaling in and out
Scaling in means entering part of the position first and adding later if the trade behaves as expected. It reduces the cost of being early, but it also means the average entry is worse if the trade runs immediately, and it complicates the risk calculation because each add changes the average stop distance. If you scale in, decide the total risk first and divide it across the entries; do not add because the first entry is in profit.
Scaling out means taking partial profit at a level and letting the rest run. It reduces the emotional pressure of a winner, but it also caps the trades that pay for the losers. There is no universally correct approach. The important discipline is to write the plan before the trade: how many units, at what levels, and what the risk is at each stage. Improvising the exits turns a measured position into a discretionary one.
When to reduce size
Size should come down after a drawdown, after a change in the method, and whenever the market’s volatility rises sharply. A method that risked 1% in a calm market may be risking 2% in effective terms when the average daily range doubles. Reducing size is not a sign of weakness; it is how a trader survives a regime change long enough to adapt.
Size should also come down when life changes. A new job, a mortgage, a family responsibility or a period of poor sleep all affect the ability to follow a plan. The capital is the same, but the person managing it is not. A smaller position is a rational response to a higher chance of a bad decision.
The mistakes
- Sizing from the margin available. The broker’s limit is not your risk budget. It is the maximum the broker will allow, not the maximum you should take.
- Rounding up. If the calculation gives 37 shares, buying 50 because it is a round number increases the risk by a third.
- Ignoring costs. Brokerage, STT and slippage are part of the loss when a stop is hit. Include them or accept that the real risk is higher.
- Increasing size after a win. Confidence is not evidence. Size should follow the plan, not the last outcome.
- Revenge sizing. Doubling the position to recover a loss is the fastest route from a bad day to a bad month.
- No written record. If you do not record the risk per trade, you cannot tell whether a drawdown is normal or a sizing error.
- Position size comes from capital, risk per trade and stop distance.
- Tighter stops allow larger positions, which are more sensitive to gaps and slippage.
- Risk 0.25% to 1% per trade while learning; the exact figure is a decision.
- Place stops beyond structure, not at an arbitrary percentage.
- Budget risk at the portfolio level, not only trade by trade.
- Record the planned and realised risk in a journal.
If your journal shows that your losses are consistently larger than planned, the problem is usually sizing or execution, not analysis. The trading course covers position sizing, expectancy and execution discipline. The advanced trading course works on portfolio risk and drawdown using your own record. Read the risk disclosure before increasing size.