Dear Liz: What is the difference between ETFs, mutual funds and index funds?

Answer: Index funds are a type of mutual fund. Mutual funds and ETFs both allow you to buy a diversified mix of investments, but they’re structured differently.

Mutual fund shares are usually priced once a day, based on the value of their underlying assets minus liabilities. Investors buy and sell without knowing precisely what the share price will be, since that’s calculated after they place their orders with the mutual fund company. ETFs, or exchange-traded funds, by contrast, trade throughout the day on stock exchanges and can be worth more or less than the underlying investments, depending on demand.

Most mutual funds are actively managed. That means the underlying investments may frequently change as the fund manager tries to “beat the market” and get a better return than a market index or benchmark such as the Standard & Poor’s 500. All that trading increases a fund’s costs and usually doesn’t result in a higher return.

By contrast, index mutual funds just try to match the market benchmark. This is known as passive management. Less trading leads to lower costs and typically better returns.

Most ETFs are passively managed and have even lower costs than typical index mutual funds. ETFs are the investment of choice for robo-advisors, which offer automated investment management, but they also can be an inexpensive way for individuals to invest. Also, ETFs don’t have the investment minimums that can sometimes be a barrier to start investment with mutual funds.