Incorrect.
The trade date is the day a trade executes. The shares are sold and the balance is reflected in your account; you can trade off the balance if your account is set up as a margin account. If not, then you have to wait for those funds to clear, which is called the settlement date. The settlement date on all US stocks is referred to as “T+2”, meaning that it takes two days for the funds to clear and be officially deposited/settled.
The last trading day of 2019 is today, December 31. If you sell for a loss today you can deduct it against any other capital gains of that current year (2019).
The only exception is if you are “shorting“ a stock. If you cover a “short” position for a loss, then you report it as of the settlement date.
As always, LONG & STRONG LQMT
Happy News Years to ALL !