Net asset value (NAV) is the per-share value of a mutual fund or ETF, calculated by dividing the total value of the fund's holdings minus any liabilities by the number of outstanding shares. For mutual funds, NAV is calculated once per day after the market closes, and it's the price at which you buy or sell shares. ETFs also have a NAV, but because they trade on an exchange throughout the day, their market price can differ slightly from NAV. Knowing the NAV helps you understand what your fund shares are actually worth based on the underlying investments. It's a key figure to track when monitoring your fund's performance over time.