**The information below has not been verified for the 2020 tax year as the IRS Pub. 550 has not yet been released by the IRS.**
Per IRS Publication 550 Investment Income and Expenses (Including Capital Gains and Losses), on page 20:
Dividends Used To Buy More Stock
The corporation in which you own stock may have a dividend reinvestment plan. This plan lets you choose to use your dividends to buy (through an agent) more shares of stock in the corporation instead of receiving the dividends in cash. Most mutual funds also permit shareholders to automatically reinvest distributions in more shares in the fund, instead of receiving cash. If you use your dividends to buy more stock at a price equal to its fair market value, you must still report the dividends as income.
If you are a member of a dividend reinvestment plan that lets you buy more stock at a price less than its fair market value, you must report as dividend income the fair market value of the additional stock on the dividend payment date.
You also must report as dividend income any service charge subtracted from your cash dividends before the dividends are used to buy the additional stock. But you may be able to deduct the service charge.
In some dividend reinvestment plans, you can invest more cash to buy shares of stock at a price less than fair market value. If you choose to do this, you must report as dividend income the difference between the cash you invest and the fair market value of the stock you buy. When figuring this amount, use the fair market value of the stock on the dividend payment date.
Stocks and Bonds (on page 41):
Reinvestment right. This is the right to acquire mutual fund shares in the same or another mutual fund without paying a fee or load charge, or by paying a reduced fee or load charge.
The original cost basis of mutual fund shares you acquire by reinvesting your distributions is the amount of the distributions used to purchase each full or fractional share. This rule applies even if the distribution is an exempt-interest dividend that you do not report as income.
RECORDS: Table 4-1. This is a worksheet you can use to keep track of the adjusted basis of your mutual fund shares. Enter the cost per share when you acquire new shares and any adjustments to their basis when the adjustment occurs. This worksheet will help you figure the adjusted basis when you sell or redeem shares.
Note that any link in the information above is updated each year automatically and will take you to the most recent version of the document at the time it is accessed.