A fee that is paid out of a mutual fund’s assets to cover marketing and distribution costs of the fund or to pay commissions to brokers. The fee is usually between 0.25 percent and 1 percent of assets annually. It is included in the fund’s expense ratio, which is deducted from your 401(k) account each year. You can find the 12b-1 fee listed in the mutual fund’s prospectus; look in the fee table..