What an expense ratio measures in a fund

The expense ratio is the percentage of a fund's average net assets that the fund pays each year to cover its operating costs. An expense ratio of 0.50 percent means the fund sets aside about $0.50 a year for every $100 invested. Shareholders rarely receive a bill for it. Instead, the cost is taken out of the fund's assets, so the return you see is slightly lower than the return the portfolio itself earned before those costs.

The expense ratio applies every day the fund operates, whether or not its returns are strong. This differs from a transaction fee, which you pay when you buy or sell. The expense ratio is a yearly figure, and it is typically shown with two decimal places, which makes it straightforward to compare across funds that disclose it the same way.

How the figure is calculated and what it covers

The calculation itself is simple. A fund's annual operating expenses are divided by its average net assets over the year. If a fund with $500 million in average net assets spends $2.5 million on operating costs in a year, its expense ratio is 0.50 percent. Because the figure is a ratio, growth in assets can sometimes lower it if costs do not rise as quickly, and a shrinking fund can see it rise even when its spending stays the same. The figure is generally based on the most recent fiscal year, so it describes past spending rather than a promise about future costs.

The figure generally covers the fund's management fee, which pays the investment adviser, along with administrative costs such as recordkeeping, shareholder servicing, custody, accounting, legal and audit fees. Where a fund charges one, it also covers a distribution or service fee, sometimes called a 12b-1 fee, which pays for marketing and shareholder services. These costs are pooled and charged in proportion to the fund's assets.

The expense ratio does not capture everything. Brokerage commissions and other costs the fund incurs when buying and selling securities are generally not included, so a fund with heavy trading can cost more than its headline figure suggests. Sales loads, which are charged when shares are bought or sold, appear separately in the fee table under shareholder fees. Some funds also show additional lines, such as the costs of other funds they invest in, so reading the full table is more reliable than relying on a single number.

Finding the figure and comparing funds fairly

The expense ratio appears in the fund's prospectus, usually in a fee table near the front, and it is repeated in the summary prospectus and in shareholder reports and fact sheets. Many funds show two versions: a gross expense ratio before any fee waivers and a net expense ratio after waivers or reimbursements. A waiver is an agreement by the adviser to absorb some costs, and it can end or change. The net figure reflects the waiver in place, so check the prospectus for how long a waiver is expected to last. The fee table also includes an example showing the dollar cost of a $10,000 investment over one, three, five and ten years, based on a hypothetical 5 percent annual return. It is a comparison tool, not a forecast of what the fund will earn.

To compare funds fairly, look at funds of the same kind. Expense ratios vary widely between bond and stock funds and between actively managed and index funds, so comparing across categories can mislead. Convert the percentage into dollars using the amount you plan to invest: 0.25 percent on $20,000 is $50 a year, and on $10,000 the gap between a 0.10 percent fund and a 1.00 percent fund is $90 a year. Then check whether the lower figure belongs to a fund with a similar strategy, benchmark and risk profile, because a cheaper fund with a different mix is not an equal alternative.

How the expense ratio shows up in returns

A fund accrues its operating expenses each day, so a small slice of the annual figure is recorded against the fund's assets every day, and the net asset value per share reflects that charge.

This matters when you read a performance table. The total returns a mutual fund reports are calculated after its ongoing expenses have been deducted, so the expense ratio is already built into those figures. Subtracting it again counts the same cost twice and understates what the fund delivered. Exchange-traded funds report returns net of expenses in the same way.

Some presentations also show gross returns, calculated before expenses. Those figures can show how a strategy performed before costs, but they are not what a shareholder kept. When two figures are compared, make sure both are net of expenses or both are gross.

A fund's expense ratio is a clear, disclosed number, which is part of its appeal as a comparison point. Read it alongside the fund's objective, its turnover and the rest of its fee table before deciding how much weight it should carry. Because the expense ratio is a percentage, the dollar amount it represents rises as the invested balance grows, which is worth remembering as contributions build up over the years.