The 180-day exchange period is the deadline to close on replacement property: 180 days from the relinquished sale or the tax-return due date, whichever comes first.
The 180 days run at the same time as the 45-day identification period, not after it, so an investor who uses all 45 days to identify has about 135 days left to close. The deadline is the earlier of 180 days after the sale or the due date of the investor's tax return for that year, which can shorten the period for a sale late in the year unless an extension is filed. These dates are not extended for weekends, holidays, or financing delays, which is why lining up the lender, inspections, and title early matters.