Position Sizing

I decide how much I'm willing to lose before I decide how much to buy.

• Calculate how many shares to buy in a single trade using Position Size = Capital Risked ÷ (Entry Price − Stop-Loss Price).
• Distinguish capital deployed (total money used to enter a trade) from capital at risk (money actually lost if the stop-loss is hit).
• Explain why risk-per-share, not entry price alone, is the true driver of position size.
• Connect this trade-level sizing method to the portfolio-level sizing already learned, recognizing them as related but distinct tools.

You already know how to size a portfolio holding — Value of Holding ÷ Total Portfolio Value. That answers "what share of my money sits in this one stock?" This unit answers a different question: "for this one trade, how many shares should I buy?" It's the trade-level sibling of that skill, not a repeat of it.

The answer isn't "as many as I can afford." It's driven by your stop-loss — the price where you'll admit the trade was wrong and exit.

Here's the formula: Position Size = Capital Risked ÷ (Entry Price − Stop-Loss Price).

Capital Risked is the rupee amount you've decided, in advance, you're willing to lose on this one trade — often a fixed rule like 1% of your trading capital. (Entry Price − Stop-Loss Price) is your risk-per-share — how much you lose on each single share if the stop-loss gets hit. Divide the first by the second, and you get the number of shares to buy so that if you're wrong, you lose exactly the amount you decided on — no more.

Decide the rupee risk first, find the stop-loss distance second, calculate shares last.

Notice the sequence this forces on you: decide the rupee risk first, find the stop-loss distance second, calculate shares last. Never work backward from how much cash happens to be sitting in your account.

This also splits one number into two that traders often confuse. Capital Deployed is the total money tied up in the trade (shares × entry price). Capital at Risk is the money you actually lose if the stop-loss hits (shares × risk-per-share). These are not the same number, and mixing them up is how traders misjudge how much danger they're really in.

The formula manages risk — it doesn't erase it.

A stop-loss can gap in a fast-moving market, so the real loss can exceed the planned one. The formula defines your intended risk; it can't guarantee the market honors it.

Suppose a trader has ₹5,00,000 in trading capital and follows a simple personal rule: never risk more than 1% of that capital on a single trade. One percent of ₹5,00,000 is ₹5,000 — that's the Capital Risked for this trade, decided before anything else.

The trader wants to enter a stock at ₹500, with a stop-loss placed at ₹480. That ₹20 gap is the risk-per-share — the amount lost on every single share if the stop-loss is hit.

Now the formula does the work: Position Size = ₹5,000 ÷ ₹20 = 250 shares.

Buying 250 shares at ₹500 each means ₹1,25,000 of capital deployed — that's the total money tied up in the position. But the capital at risk, if the stop-loss is hit, stays capped at exactly ₹5,000 (250 shares × ₹20). That's a full ₹1,20,000 difference between what's deployed and what's actually at risk, on the exact same trade.

This is the moment worth sitting with: the trader isn't asking "how much can I spend?" They already answered "how much am I willing to lose?" first, and the number of shares simply followed from that answer.

Point: Position size is reverse-engineered from acceptable rupee loss and stop-loss distance, not from available capital — and capital deployed and capital at risk are two distinct numbers that a trader must never conflate.

Look at what happens if the stop-loss distance changes but the rupee risk stays fixed. Say the trader still risks ₹5,000, but places a wider stop — ₹460 instead of ₹480, making risk-per-share ₹40 instead of ₹20. Now Position Size = ₹5,000 ÷ ₹40 = 125 shares, half as many as before. A wider stop feels like "more breathing room," but the formula forces a smaller position to keep the rupee risk exactly the same. Safety here doesn't come from how wide or narrow the stop is — it comes from keeping the rupee amount at risk constant no matter where the stop sits. That's also why this formula and your Level 3 portfolio formula aren't in competition. Level 3 asks "what percentage of my total portfolio is this holding?" — a question about how your money is spread across many positions. This formula asks "how many shares can I hold in this one trade given my stop-loss and my acceptable rupee loss?" — a question about a single trade's exit plan. Both come from the same instinct — decide how much you're willing to lose — just applied at two different levels. You'll use both, for different reasons, often on the very same trade.

• Treating capital deployed (₹1,25,000) as the same thing as capital at risk (₹5,000). — In everyday spending, the money you hand over is the money at stake, so it feels natural to assume buying shares works the same way. Fix: Always ask two separate questions after sizing a trade: 'how much money is tied up?' and 'how much do I actually lose if the stop-loss hits?' They are rarely the same number.
• Assuming this formula is just Level 3's portfolio-percentage sizing repeated. — Both are called 'position sizing' and both answer 'how much,' so they sound identical on the surface. Fix: Remember the different question each answers: Level 3 asks what share of your whole portfolio one holding takes up; this formula asks how many shares one single trade can hold given its stop-loss distance.
• Believing a wider stop-loss is automatically safer because it gives the trade more room. — More room to move feels like less chance of getting stopped out by normal price noise. Fix: Remember the formula shrinks your position size as the stop widens, to keep rupee risk fixed — safety comes from a constant rupee risk, not from stop width.
• Believing the formula guarantees you'll only ever lose the calculated amount. — The formula spits out a precise, clean number like ₹5,000, which feels like a locked-in ceiling. Fix: Treat the number as your intended, planned risk — not a guarantee. Remember stop-losses can gap in fast markets, so the real loss can exceed the plan.

• Position Size = Capital Risked ÷ (Entry Price − Stop-Loss Price) — it sizes a trade by how far your stop-loss sits, not by how much cash you have.
• Decide the rupee risk first, find the stop-loss distance second, calculate shares last — never work backward from available capital.
• Capital Deployed (total money used to buy) and Capital at Risk (money lost if stopped out) are two different numbers — never confuse them.
• This trade-level formula is the sibling of your Level 3 portfolio-percentage skill, not a repeat of it — same instinct, different lens.
• A stop-loss defines your intended risk; it manages loss, it does not guarantee or eliminate it.

Q1. What is the correct formula for trade-level position sizing?

• Position Size = Capital Risked ÷ (Entry Price − Stop-Loss Price)
• Position Size = Value of Holding ÷ Total Portfolio Value × 100
• Position Size = Total Capital ÷ Entry Price
• Position Size = Entry Price ÷ Stop-Loss Price Answer: Position Size = Capital Risked ÷ (Entry Price − Stop-Loss Price) — This formula sizes a single trade based on how far the stop-loss sits from the entry price, not on total available capital. The Level 3 formula (% of portfolio) answers a different question.

Q2. A trader buys 250 shares at ₹500 each, with a stop-loss at ₹480. What is the 'capital deployed' for this trade?

• ₹1,25,000
• ₹5,000
• ₹20
• ₹4,80,000 Answer: ₹1,25,000 — Capital deployed is the total money tied up in the trade: 250 shares × ₹500 entry price = ₹1,25,000. This is different from capital at risk, which is only ₹5,000 (250 shares × ₹20 risk per share).

Q3. Capital deployed and capital at risk always mean the same amount of money in a trade. Answer: False — Capital deployed is the total money used to buy the position, while capital at risk is only the money actually lost if the stop-loss is hit. A trade can deploy ₹1,25,000 while risking only ₹5,000 — these are two separate numbers, defined by the stop-loss distance, not the entry cost.

Q4. A trader decides to risk ₹8,000 on a trade. They want to enter a stock at ₹300, with a stop-loss at ₹280. How many shares should they buy? Answer: 400 shares — Risk-per-share = Entry Price − Stop-Loss Price = ₹300 − ₹280 = ₹20. Position Size = Capital Risked ÷ Risk-per-share = ₹8,000 ÷ ₹20 = 400 shares. If the stop-loss is hit, the loss stays capped at exactly ₹8,000.

Q5. A trader risks ₹10,000 per trade. Entry ₹500, stop-loss ₹480 → 500 shares. He tightens the stop to ₹495 and buys 2,000 shares instead, telling himself: "Same ₹10,000 risk, just a tighter stop, no problem." What is he not accounting for? Reveal: Weak: agrees — same rupee risk, no issue. Strong: notices a tighter stop gets hit by ordinary price noise far more often, so even though each stop-out still costs ₹10,000, he'll now hit that loss more frequently — the real risk went up even though the per-trade cap didn't.