You have followed every rule. Three trades, 1 percent risk on each, stops set by structure. Then all three lose within an hour of each other and you are down 3 percent on what felt like a careful day. That is forex correlation risk, and it catches disciplined traders far more often than reckless ones.
01 Every pair contains two bets
A currency pair is not one instrument, it is a relationship between two currencies. Buying EUR/USD is simultaneously a bet that the euro strengthens and a bet that the US dollar weakens. You cannot separate them.
Which means the moment you open a second position that shares a currency, your two trades are no longer independent. They may be the same trade in different clothing.
Three positions, three stops, three lots of homework. One outcome. If the US dollar strengthens on a jobs number, every one of them goes wrong at the same moment, and the 1 percent rule you were so careful about has quietly become a 3 percent rule.
02 Positive, negative and nothing much
Correlation describes how closely two pairs move together. EUR/USD and GBP/USD are usually positively correlated, because both are largely a view on the US dollar. EUR/USD and USD/CHF tend to move in opposite directions, because the US dollar sits on opposite sides of each.
Negative correlation is its own trap. Buying EUR/USD and buying USD/CHF at the same time is close to holding no position at all, while paying spread on both. You are not hedged in any useful sense, you are just paying twice to stand still.
These relationships also drift. Pairs that tracked each other for months can decouple when a central bank changes course, so correlation is something to check periodically rather than memorise once.
03 A rule you can actually apply
You do not need a correlation matrix to trade well. You need one habit: before opening a position, look at what you already hold and ask which currency you are really exposed to. Then cap it. A workable rule is that total risk on any single currency stays within your normal per-trade limit, so three US dollar trades at 1 percent each become three at roughly 0.33 percent, or simply the best one at 1 percent.
Most of the time the best one at full size is the better answer. Three mediocre versions of the same idea are not diversification.
Your account is 10,000 US dollars and your limit is 1 percent, so 100 US dollars per trade. You like the look of long EUR/USD, long GBP/USD and short USD/JPY. All three are short the US dollar. Taken at full size that is 300 US dollars riding on one macro view. Applying a per-currency cap, you either split the 100 US dollars three ways, or you pick the cleanest chart and take that one at 100 US dollars. Same conviction, honest accounting.
Believing that trading several pairs is automatically diversification. Spreading money across four US dollar pairs is not diversifying, it is concentrating with extra steps and extra spread. Genuine diversification means exposure to something that can move independently.
- You are long EUR/USD and long GBP/USD. What single event hurts both?
- You are long EUR/USD and long USD/CHF. Roughly what position do you hold overall?
- Why is opening four US dollar pairs at 1 percent each not the same as risking 1 percent?
Show answers
1) A broad US dollar rally. 2) Close to flat, while paying the spread on both. 3) Because they share a driver, so they tend to lose together. Your real exposure to the US dollar is nearer 4 percent.
- Every pair is a bet on two currencies, so positions sharing a currency are not independent.
- Several correlated trades at 1 percent each add up to a single much larger bet.
- Negatively correlated positions can cancel out and leave you paying spread for nothing.
- Cap total risk per currency, or take the single best setup at full size instead.
Pairs sharing a currency on the same side usually do, such as EUR/USD, GBP/USD and AUD/USD, which are all partly a bet against the US dollar. Pairs with the shared currency on opposite sides, such as EUR/USD and USD/CHF, tend to move against each other.
Yes, provided you size them as one position rather than two. Split your normal risk between them instead of applying it to each, or accept that you have deliberately doubled your exposure to one currency.
No. They shift as interest rate expectations and risk appetite change, and a relationship that held all year can break within a week of a central bank surprise. Check rather than assume.
Further reading: Euro foreign exchange reference rates, published daily by the European Central Bank, where you can watch several euro crosses move together over time.
See how sessions change which currencies move together