Position Sizing and Portfolio Heat

Before I open a new position, I ask not just 'is this trade safe on its own?' but 'how much of my whole portfolio is now at risk?'

• Define portfolio heat as the total capital at risk across all open positions, expressed as a percentage of total capital.
• Explain why several individually 'safe' positions can combine into a dangerous total exposure (risk stacking).
• Calculate current portfolio heat by summing risk per position across multiple open trades.
• Decide whether a new position can be added by checking remaining heat capacity against a personal heat ceiling.

Here's the problem with checking trades one at a time: your capital doesn't know it's split into "Trade A," "Trade B," and "Trade C." It's one pool. If three trades go wrong on the same day, all three losses come out of that same pool, together.

Portfolio heat is the name for measuring that pool's total risk. It's simple: take the risk (the amount you'd lose if the worst case happens) on every open position, add them all up, and express that total as a percentage of your total capital.

Watch how fast this adds up. Say you follow the Level 4 rule of never risking more than 5% of capital on a single trade. You open Position A at 5% risk. Safe, by the rule. You open Position B at 5% risk. Also safe, by the same rule. You open Position C at 5% risk. Safe again. But add them together: 5% + 5% + 5% = 15% of your entire capital is now on the line, at the same time, if things go badly. No single check ever showed you that number, because no single check was ever asking that question.

The real check isn't "is this trade small enough?" — it's "how much room is left under my ceiling?"

That's risk stacking: positions that each pass the individual safety test can still combine into a total that fails the portfolio safety test. This is why you also need a heat ceiling — a personal limit you set for yourself, like "I will never let my total portfolio risk go above 15%." It isn't a market rule. It's a boundary you draw so a fourth trade doesn't sneak your real exposure past what you'd ever knowingly accept.

So the real check before opening any new position isn't "is this trade small enough?" It's "how much room is left under my heat ceiling once I add this trade to everything I already hold?" If your ceiling is 15% and you're already at 15%, the honest answer is: no room. Not because the new trade is badly sized — it might be perfectly sized on its own — but because your pool is already full.

That's the shift worth remembering.

This is where judgment does the work a formula can't. The heat number tells you what's true right now, but it doesn't guarantee what happens next — a bad move can still cost more than your calculated risk suggested. The formula's job is to make your exposure visible, not to make it safe.

Rohan trades index derivatives on the side, using the Level 4 rule he learned: never risk more than 5% of capital on one trade. His account has ₹4,00,000 in it.

Right now Rohan has three open positions:

• Position A (Nifty futures): risks 5% of capital = ₹20,000
• Position B (Bank Nifty options): risks 5% of capital = ₹20,000
• Position C (a stock futures position): risks 5% of capital = ₹20,000

Each one, checked alone, passed his safety rule. None of them individually worried him.

Then Rohan adds them up: 5% + 5% + 5% = 15% of his total capital, or ₹60,000, is at risk right now if all three positions hit their worst case at the same time.

Rohan had set himself a personal heat ceiling of 15% months ago — a rule that he'd never let his total risk across all trades cross that line. Looking at the number now, he sees he's sitting exactly at it. ₹60,000 out of ₹4,00,000 is already on the table.

A friend messages him about a fourth trade — a promising options setup that, checked on its own, would only risk another 5% of capital. Sized alone, it looks perfectly fine, well within the single-trade rule. But Rohan does the portfolio check first: 15% already committed, plus 5% more, equals 20% total heat — five percentage points past his own ceiling.

He passes on the trade. Not because it was badly designed, but because his pool of capital has no room left for it right now. He would have to close or reduce one of his existing three positions before adding a fourth.

Point: Summing risk per position across all open trades reveals total exposure that no single-trade check would ever show, and that total can already consume the entire heat ceiling even when every individual position passed its own safety rule.

One more layer worth knowing: correlation. If Position A, B, and C are all betting on the same sector, or all move with the same market trend, they don't just add up on paper — they can lose at the same real moment, for the same real reason. Two "unrelated-looking" trades that both depend on, say, IT stocks rising can both get hit by the same bad news. When positions are related like this, the effective risk of them failing together is higher than the simple sum suggests. This doesn't change the math you do — you still add risk per position the same way — but it should make you more cautious about how close you let your total get to the ceiling when your positions aren't truly independent. This is a flag for judgment, not a new formula to learn here; deciding exactly how much extra caution correlated positions deserve is a deeper skill for later.

• Believing that if every individual trade passes the single-trade safety check, the whole account must be safe. — Level 4 trained learners to check safety one trade at a time, so that habit carries forward even when multiple positions are open at once. Fix: After sizing any single trade, add its risk to the risk of every other open position and compare that total to your heat ceiling — not just to the single-trade rule.
• Treating the amount of money invested in positions as the same thing as the risk of losing money. — Total capital deployed is an easy number to see at a glance, so it feels like the natural thing to track, even though it isn't what you'd actually lose. Fix: Track potential loss per position (what you'd lose at the worst case, like a stop-loss level), not how much money is simply invested — heat is about risk, not deployment.
• Assuming that following a portfolio heat formula or staying under a heat ceiling guarantees you're safe. — A formula with clean percentages feels precise and authoritative, so it's tempting to treat it as a promise rather than a guide. Fix: Use the heat number as a discipline tool that makes your exposure visible, and still exercise judgment — real losses in a sharp market move can exceed what the calculation suggested.

• Portfolio heat is the total risk across all your open positions, added together and shown as a percentage of your total capital.
• Several trades can each pass the single-trade safety check and still combine into a dangerous total — this is risk stacking.
• Before opening a new position, check how much room is left under your personal heat ceiling, not just whether the new trade alone is small enough.
• A heat ceiling is a discipline boundary you set for yourself; it doesn't come from the market and it doesn't guarantee safety.
• Treat your capital as one shared pool to protect, not a set of separate bets you check one at a time.

Q1. What does "portfolio heat" measure?

• The total risk (potential loss) across all open positions, as a percentage of total capital
• The number of open positions in an account
• The total money invested across all positions, regardless of potential loss
• The profit earned from all open positions so far Answer: The total risk (potential loss) across all open positions, as a percentage of total capital — Portfolio heat adds up the risk (what you'd lose in a worst case) from every open position and shows it as a percentage of your total capital - it's about potential loss, not how much money is simply deployed or how many trades you hold.

Q2. A trader has three open positions, each individually sized to risk only 4% of capital using the single-trade safety rule. Why might this trader still be in danger?

• Because the three risks can add up to 12% of capital at risk if all positions lose at once, even though each looked safe alone
• Because single-trade safety rules are never accurate for any trade
• Because having three positions automatically means the trader is unskilled
• Because only options positions, never futures, can be sized safely Answer: Because the three risks can add up to 12% of capital at risk if all positions lose at once, even though each looked safe alone — This is risk stacking: each trade passing its own single-trade check doesn't mean the combined portfolio is safe, because the individual risks can sum into a much larger total exposure that no single-trade check ever revealed.

Q3. A trader's personal heat ceiling is 12% of capital. Currently, three open positions together already put 12% of capital at risk. A new position, sized on its own, would risk another 4% of capital. Should the trader open this new position?

• No, because adding it would push total portfolio heat to 16%, past the 12% ceiling
• Yes, because the new position is well within the single-trade sizing rule
• Yes, because the heat ceiling only applies to the very first position opened
• No, because the trader should never open more than three positions in total Answer: No, because adding it would push total portfolio heat to 16%, past the 12% ceiling — Even though the new trade looks fine on its own, the real check is whether there's room left under the heat ceiling. Since current heat (12%) plus the new risk (4%) equals 16%, which exceeds the 12% ceiling, there's no room - the trader would need to reduce an existing position first.

Q4. A trader carefully keeps portfolio heat under his 5% ceiling and says: "I've done the math, so I literally cannot lose more than 5% no matter what happens." Does staying under the heat ceiling guarantee that cap holds no matter what? Reveal: Weak: yes, the calculation is a hard guarantee. Strong: portfolio heat is a discipline tool that makes exposure visible, it doesn't remove uncertainty — in an extreme market move, actual losses can still exceed what the calculation suggested.