Is there a calculator (HTML/Excel) available anywhere that calculates the interest costs for FX trades? Failing that an article that explains in understandable terms how it is calculated, so I can create my own formula. I am with IB and their explanatory data/information does not reconcile with what they have charged me. I had always understood that unless putting on carry trades, the cost of financing in FX trades was minimal, as one credit offsets the other debit. It appears that IB have charged me the following: Trade: Long (47,500) USD/MXN Holding period 7 days. Total int cost USD 24.18 Trade: Short(25000) USD/SEK Holding period 7 days. Total int cost USD 9.10 This was an arb trade where the overall profit was around $110, but if the carrying cost is $33.12 then it is significant in relation to profit margins in this type of trading. Any light that can be shone on my ignorance wld be appreciated.