NAV is short for Net Asset Value. It is calculated by dividing the net value of the assets held under a mutual fund by the total number of outstanding units. The NAV of a mutual fund is calculated at the end of every day. This is because the market value of the assets under the mutual funds will change daily, and so will the fund's NAV. As such, NAV helps investors keep track of the fund's performance on a day-to-day basis.