PairsTrading

What Is Pairs Trading?

Pairs trading is a strategy where you exploit divergences between correlated assets. You go long one asset, short another, and profit when they revert to their normal relationship.

It’s “market-neutral” because your long and short positions offset each other. You don’t care if the market goes up or down — you care if the two assets diverge.

How Pairs Trading Works

Normal state:

• EUR/USD and GBP/USD move together (correlation = 0.90)
• When EUR rallies, GBP usually rallies too
• When EUR falls, GBP usually falls too

Pairs trade opportunity:

• EUR/USD rallies 200 pips
• GBP/USD only rallies 50 pips (divergence)
• Historical correlation suggests GBP should have rallied more
• You: Go long GBP/USD, short EUR/USD
• Bet: GBP catches up or EUR falls back, closing the gap

Pairs Selection

Best forex pairs for pairs trading:

1. EUR/USD & GBP/USD — historically 0.85-0.95 correlation
2. AUD/USD & NZD/USD — historically 0.85+ correlation
3. EUR/USD & CHF/USD — inverse correlation (0.70-0.80 negative)
4. USD/JPY & USD/CHF — both “safe haven” currencies

How to check correlation:

1. Pull 1-year daily data for two pairs
2. Calculate correlation coefficient
3. If above 0.80, they’re candidates
4. Test the spread behavior over time

The Spread

In pairs trading, you track the “spread” — the price difference between the two pairs.

Example:

• EUR/USD: 1.1000
• GBP/USD: 1.3000
• “Spread” = ratio or difference between them

You don’t trade individual pairs; you trade the spread. When the spread reaches historical extremes, you bet it reverts.

Setting Up a Pairs Trade

Step 1: Calculate historical spread

• Over 3-6 months, track EUR/USD - GBP/USD spread
• Find the mean (average spread)
• Find the standard deviation (how far spreads typically deviate)

Step 2: Identify divergence

• Spread moves 2 standard deviations from the mean
• This is extreme — historically rare
• Probability high that it reverts

Step 3: Enter the trade

• Long GBP/USD, short EUR/USD (if GBP is underperforming)
• Equal notional size (same risk on both sides)
• Target = when spread returns to mean

Step 4: Exit

• Exit when spread reverts to mean (take profit)
• Exit if correlation breaks (cut loss to avoid holding broken pair)
• Use time stops (hold for max 30-60 days)

Position Sizing in Pairs Trading

The goal is equal notional exposure:

• If you’re long 1 standard lot GBP/USD (100K)
• And short EUR/USD (100K)
• Market moves against both, but your P&L is neutral
• You profit only if GBP outperforms EUR

Practical example:

• Buy 0.5 GBP/USD
• Sell 1.0 EUR/USD (because EUR is more volatile)
• Adjust sizes so price moves affect both sides equally

Risk in Pairs Trading

Correlation breakdown:

• Historical correlation breaks permanently
• Your two pairs stop moving together
• Trade becomes a directional bet (which you can’t predict)
• Account gets hit hard

Solution:

• Monitor correlation continuously
• Exit if correlation drops below 0.70
• Don’t hold pairs trades longer than 60 days
• Track correlation by season (correlations change over time)

Using Pairs Trading in Your Journal

Track:

• Which pairs had consistent 0.85+ correlations?
• When did correlations break?
• Which spread divergences actually reverted?
• What was your hit rate on mean reversion?
• Did longer-duration pairs trades work better or worse?

Pairs Trading by Timeframe

• Daily chart — longer holds, smaller daily moves, need larger spread divergence
• 4-hour chart — medium-term, better entry/exit precision
• 1-hour chart — scalping pairs, tight stops required, more trades

The Takeaway

Pairs trading removes the hardest part of trading — predicting direction. Instead, you’re betting on mathematical reversion. When two correlated assets diverge, they usually come back together. That’s your edge.

The risk is correlation breakdown. Manage it by monitoring correlations, exiting when they weaken, and using time stops. Done right, pairs trading is one of the most mechanical, reliable strategies available.

But it requires discipline, good position sizing, and patience. You’re not betting on market direction — you’re betting on mean reversion. That’s a different skillset entirely.