Open positions:
Position #1: 1,000,000 BUY USDJPY – Margin Used for Position: 2,000 Position #2: 1,000,000 BUY USDJPY – Margin Used for Position: 5,000 Position #3: 1,000,000 BUY USDJPY – Margin Used for Position: 10,000 Total Margin Used: 17,000 USD
Step 1: Trader entirely closes Position #2. This results in:
Total Margin Used: 2,000 + 10,000 = 12,000 USD
Step 2: Open one more position for 1,000,000 USDJPY (Position #4). This results in:
Margin Position #4: 1,000,000 / 100 (leverage) = 10,000 USD margin;
Now we have three positions.
Even though the exposure is the same as before (3 million), the margin is significantly higher because the margin of Position #3 has not recalculated.
Total Margin Used: 12,000 + 10,000 = 22,000 USD
Step 3: Partially close Position #4 and Position #1 by 500,000 each. This results in:
Margin Position #4: 10,000 / 2 = 5,000; Margin Position #1: 2,000 / 2 = 1,000. Summary: Position #1: 500,000 BUY USDJPY – Margin Used: 1,000 USD; Position #3: 1,000,000 BUY USDJPY – Margin Used: 10,000 USD; Position #4: 500,000 BUY USDJPY – Margin Used: 5,000 USD. Total Margin Used: 1,000 + 10,000 + 5,000 = 16,000 USD