對不起，半瓶子醋。

對不起，和26 USC 121（c）混淆了。

https://www.law.cornell.edu/uscode/text/26/121

(c)Exclusion for taxpayers failing to meet certain requirements

(1)In generalIn the case of a sale or exchange to which this subsection applies, the ownership and use requirements of subsection (a), and subsection (b)(3), shall not apply; but the dollar limitation under paragraph (1) or (2) of subsection (b), whichever is applicable, shall be equal to—

(A)

the amount which bears the same ratio to such limitation (determined without regard to this paragraph) as

(B)

(i)the shorter of—

(I)

the aggregate periods, during the 5-year period ending on the date of such sale or exchange, such property has been owned and used by the taxpayer as the taxpayer’s principal residence; or

(II)

the period after the date of the most recent prior sale or exchange by the taxpayer to which subsection (a) applied and before the date of such sale or exchange, bears to

(ii)

2 years.