Can I do Tax-loss harvesting selling on Dec. 31?

It says: Timing:To count for the current tax year, all sales must be settled by the last trading day of the calendar year (usually December 31st).

But if I do it in my margin accts, it will settle on the same day.

Reporting:You must report your capital gains and losses onForm 8949andSchedule D (Form 1040)when filing your taxes.