The cost of owning a mutual fund that is deducted from your 401(k) account. Basically, it’s the amount you pay each year to the fund to cover operating expenses and management and 12b-1 fees. Expressed as a percentage of the net asset value of your investment in the fund. Expense ratios vary across the different types of funds.
Look for the expense ratios in your 401(k) account statement, summary plan description, summary annual report, or your plan’s website. They also appear in the fund’s prospectus.