The Big O and IB seem to be the only two dealer/marketmakers that I know of that treat interest earned correctly in Retail Spot Forex. They pay it to the balance directly and report that portion to the IRS as interest earned. There actually are Fund managers in Retail spot Forex too! I am curious if they are paid from the investors, on their balance or NAV? Since most all the other dealer/marketmakers adjust the price quote at daily rollover time the "upl" adjusts instead of the balance. Michael B.
The standard industry practice on the institutional buy side has always been to base all types of client fees on account NAV, marked to market. Regardless of asset classes involved. That's what I still do. If you think of it, that's really the only fair way to do it, barring some extremely unusual circumstances. For instance, an illiquid asset, temporarily or not.