A type of mutual fund that charges its holders 12B-1 fees instead of up-front or back-end commissions. 12B-1 funds take a portion of assets held and use them to pay expense fees and distribution costs. These costs are included in the fund's expense ratio and are described in the prospectus.

The name 12B-1 comes from the Investment Company Act of 1940's Rule 12B-1, which allows fund companies to act as distributors of their own shares. Rule 12B-1 further states that a mutual fund's own assets can be used to pay distribution charges. Originally, the rule was intended to pay advertising and marketing expenses; today, however, a very small percentage of the fee actually goes toward these costs.