Let's say we incur a short term capital loss on a stock in December, while holding off trading the same stock until February next year. Technically, more than 30 days pass after the loss. However, the financial year ends before the 30 days pass. When reporting taxes for the past year, is the above loss disallowed due to wash sale rule? I suspect that it will not count as a wash sale. Is that why brokers wait until end of January to create tax forms, to be sure about wash sale properties of securities traded in December?