Foreign currency的税务规定查section 988。
(A) In general
Except as otherwise provided in this section, any foreign currency gain or loss attributable to a section 988 transaction shall be computed separately and treated as ordinary income or loss (as the case may be).
但是对于forward contract, futures contract这些可以elect成captial gain，
(B) Special rule for forward contracts, etc.
Except as provided in regulations, a taxpayer may elect to treat any foreign currency gain or loss attributable to a forward contract, a futures contract, or option described in subsection (c)(1)(B)(iii) which is a capital asset in the hands of the taxpayer and which is not a part of a straddle (within the meaning of section 1092(c), without regard to paragraph (4) thereof) as capital gain or loss (as the case may be) if the taxpayer makes such election and identifies such transaction before the close of the day on which such transaction is entered into (or such earlier time as the Secretary may prescribe).
变成capital gain以后，定义在Section 1256(g)的foreign currency contract就能享受section 1256税收优惠，需要三个条件
(2) Foreign currency contract defined
(A) Foreign currency contract The term “foreign currency contract” means a contract—
(i) which requires delivery of, or the settlement of which depends on the value of, a foreign currency which is a currency in which positions are also traded through regulated futures contracts,
(ii) which is traded in the interbank market, and
(iii) which is entered into at arm’s length at a price determined by reference to the price in the interbank market.
所谓section 1256就是楼上说的无论holding period, 都算成60% long term capital gain + 40% short term captial gain。
这里的问题是哪些交易可以elect成capital gain，首先规定的forward contract, future contract这些都可以。但是作为现货交易的spot contract行不行呢。
查了一下这竟然还是个略有争议的问题，因为section 1256(g)没有提到spot contract。