Distributions and your taxes
If you hold shares in a taxable account, you are required to pay taxes on mutual fund distributions, whether the distributions are paid out in cash or reinvested in additional shares. The funds report distributions to shareholders on IRS Form 1099-DIV after the end of each calendar year.
For any time during the year you bought or sold shares in a mutual fund, you must report the transaction on your tax return and pay tax on any gains and dividends. Additionally, as an owner of the shares in the fund, you must report and potentially pay taxes on transactions conducted by the fund, that is, whenever the fund sells securities.
If you move between mutual funds at the same company, it may not feel like you received your money back and then reinvested it; however, the transactions are treated like any other sales and purchases, and so you must report them and pay taxes on any gains.