The correlation penalty

The size haircut

Last lesson we established that correlated trades stack. This lesson is the fix: the correlation penalty. It's a haircut you give yourself when opening a second position in the same exposure bucket. The standard cut is 30 to 40 percent off the second position's risk. Some traders go heavier — 50% — when correlation is very high.

Why a haircut and not a hard cap? Because correlation lives on a spectrum. EUR/USD and EUR/GBP might move together 70% of the time on Euro-driven days, but they separate when UK-only news hits. So you don't want to refuse the trade entirely — you just want to size it like the trade you're really running, not the trade your ticket says you're running.

Concrete numbers. Account is $500, normal risk is 1% ($5). You're already long EUR/USD at $5 risk. A clean EUR/GBP setup pops up. Apply a 30% haircut: $5 × 0.70 = $3.50 risk on the second trade. Apply a 40% haircut: $5 × 0.60 = $3.00 risk. Now your combined Euro exposure is between $8 and $8.50 instead of $10. Closer to a sane single-bucket bet, even if both stops fire.

Two notes. First, the haircut is for new positions you add to an existing bucket, not for positions you opened before noticing the correlation. If you already have two full-size correlated trades open, the move is to either close one or wait. Don't average down your risk by lying to yourself. Second, the haircut compounds. Adding a third correlated position takes another 30% off — so $5 normal becomes $3.50, then $2.45. Recap: notice the bucket, cut the second trade by a third, and stop adding past two or three positions per bucket.