旧房子过户前ID也是“旧房子过户后45天以前”。

26 U.S. Code § 1031 - Exchange of real property held for productive use or investment

(a)Nonrecognition of gain or loss from exchanges solely in kind

(1)In general

No gain or loss shall be recognized on the exchange of real property held for productive use in a trade or business or for investment if such real property is exchanged solely for real property of like kind which is to be held either for productive use in a trade or business or for investment.

(2)Exception for real property held for sale

This subsection shall not apply to any exchange of real property held primarily for sale.

(3)Requirement that property be identified and that exchange be completed not more than 180 days after transfer of exchanged propertyFor purposes of this subsection, any property received by the taxpayer shall be treated as property which is not like-kind property if—

(A)

such property is not identified as property to be received in the exchange on or before the day which is 45 days after the date on which the taxpayer transfers the property relinquished in the exchange, or

(B)such property is received after the earlier of—

(i)

the day which is 180 days after the date on which the taxpayer transfers the property relinquished in the exchange, or

(ii)

the due date (determined with regard to extension) for the transferor’s return of the tax imposed by this chapter for the taxable year in which the transfer of the relinquished property occurs.