Sale of stocks that have dividends reinvested for years?

To enter Dividends, enter the amounts from your Forms 1099-DIV under Dividends in Investments and Savings.

Reinvested dividends are taxed when earned and then added to your cost basis in the investment to determine the amount of any capital gain.

For example, you invested $1,000 in a mutual fund and have earned and reinvested $50 in dividends. As a result, your cost basis is $1,050. If you sell all of your fund shares for $1,110, your taxable capital gain would be $60, not the $110 difference between what you originally paid for the fund shares and your selling value.  You need to keep track of every share.

See this article for more information on Dividends from TurboTax.

If you sold stock through a brokerage, a 1099-B should have been issued. Check with the company if you didn't receive it.

To enter the stock transactions, go to Wages and Income and scroll down to Investments and Savings.

From there:

1. Scroll down and click on the box "+Add investments"
2. Click Continue
3. Select one of the brokerages that appears in order to import their data, or click Enter a Different Way
4. Click on the appropriate box that represents the type of investment you are entering. Choosing to enter Stocks and Bonds, or Cryptocurrency will lead you to the entry screens for your Form 1099-B.

See this article for more information on the topic from TurboTax.

 [Edited 02/16/23| 11:36am PST] 

@snmf8001

you should have gotten a 1099-B that shows proceeds and tax basis. but if the tax basis is missing for some shares you may have to research that or contact the broker/trustee