Moreover, at the end of the year, the futures-based ETFs must “mark to market” all outstanding contracts and treat them as if the fund sold those contracts, and investors would realize those gains for tax purposes.

Lastly, some investors may have held an exchange traded note. Taxation of ETNs differs from that of ETFs. ETNs are a type of bond or debt security issued by an underwriting bank and subject to the credit risk of the issuer. Gains in stock, bond and commodity ETNs are all taxed at the same rate as stocks. Additionally, some currency ETFs, such as the popular suite of CurrencyShares funds, are taxed as ordinary income, no matter how long the investments are held.

For more information on ETF taxes, visit our taxes category.

Max Chen contributed to this article.