In August 2015, a single day wiped out hedge funds that believed they were "diversified" across multiple positions. Every position fell simultaneously because they were all correlated to Chinese equities. On paper: 10 separate positions. In practice: 10 copies of the same trade. Portfolio heat management is the professional risk layer that even experienced traders often skip — and pay for eventually.
Portfolio heat is the total percentage of your account at risk across all open positions simultaneously. Correlation measures how similarly two instruments move — highly correlated positions add to the same directional risk even when they appear to be different trades.
Why per-trade rules are not enough
Risking 1% per trade sounds conservative. But 8 simultaneous trades all in the same directional bias:
Total portfolio heat = 8 × 1% = 8% at risk at one time
A correlated event (flash crash, surprise central bank announcement) can close all 8 at stop loss in minutes. 8% drawdown from one event — not a gradual accumulation.
Professional maximum portfolio heat: 5–8% total at any one time.
Currency correlation
| Long on... | Also long on... | Result |
|---|---|---|
| EUR/USD | GBP/USD | Same trade (both long Dollar short, +0.90 correlated) |
| EUR/USD | AUD/USD | Similar exposure (+0.75) |
| USD/CAD | USD/CHF | Same trade (both long Dollar, +0.85) |
EUR/USD, GBP/USD, and AUD/USD long simultaneously is not "3 separate 1% trades" — it is a ~2.7% correlated bet that USD falls.
Portfolio heat audit:
Open: Long EUR/USD (1%), Long GBP/USD (1%), Long AUD/USD (0.5%), Short GBP/JPY (1%)
EUR/USD + GBP/USD = highly correlated → ~1.7% combined
AUD/USD adds ~0.35% incremental
GBP/JPY short has partial correlation with GBP/USD long → partial offset
Adjusted portfolio heat: ~3.5% — within the 5% professional limit. Acceptable.
NGX parallel: Holding GTCO, ACCESS BANK, ZENITH BANK, and UBA simultaneously = four highly correlated banking sector stocks. During a sector selloff (CBN policy change, FX restriction), all four hit stop losses simultaneously. True NGX diversification mixes sectors: banking + consumer goods (DANGFLOUR) + telecoms (MTNN) + oil services (SEPLAT) — stocks with genuinely different macro drivers.
"I am only risking 1% per trade so I am safe." Per-trade control is floor one. Portfolio heat and correlation awareness is floor two. You need both. Many traders discover this only after a correlated liquidation event takes out a week of gains in an afternoon.
Check pair correlations before adding any new position. Tools: Investing.com correlation matrix, FXCM correlation dashboard. Pairs with correlation above 0.80 should be treated as the same position. Combined heat on correlated instruments should follow the same rules as a single position.
Portfolio heat management caps total simultaneous risk at 5–8% and adjusts for correlated positions — because 8 positions in the same direction can create the same catastrophic single-event risk as one 8% position.
