How does IB calculate accrued interest on FX positions?

This may be an ignorant question (as I may be missing something completely) - but why am I being charged interest on holding a short EURUSD position?

I look at it this way... EUR is at 4.00% and USD is now at 4.50% (4.75% the other day), yet I am charged interest on the position that is long USD. I called IB customer support, but after being transferred from one department to the next in search of an answer, I gave up and have turned to the bright minds at ET.

 

How big is your position? You will not be credited interest on the 1st 10k, but you will still be charged. So if you are short 10k units of EUR/USD you will pay interest for 10k EUR but recieve interest for about only 4k USD (10000*1.4450-10000), assuming an EUR/USD rate of 1.4450.

 

I'm short 300K on that position.

 

Just had one yesterday as a matter of fact.

 

Here's a link to IB's interest rates/policy/calculations: Link

Note that Interest rates have "spreads", so there is a different rate when you're long a currency than when you're short that currency.