Think of a mutual fund's NAV, which stands for net asset value, as roughly its share price. To understand what it is, know that mutual fund prices don't fluctuate during the day. Because funds are composed of many different securities, fund companies wait until the end of trading each day, when they add up the current market value of all their holdings. They then subtract the fund's expenses for the day, such as commissions paid. The result is divided by the number of shares of the fund that exist -- and that's the NAV.

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