Nothing comes free.

While you can't predict a fund's performance from one year to the next, you can be certain that your fund isn't investing your money for free. Funds pay their bills, from salaries on down to office expenses, by charging a string of fees. Individually, they seem so small, but add them up, and the total can put a real dent in your total return.

Where do you start? Look at the fund's prospectus or in Morningstar manuals. And remember, it's best to check any fund you invest in. That's because all mutual funds charge fees--including no-load funds.

For a quick overview of how lean your fund runs, check its annual expense ratio, a figure that shows you the percentage of assets deducted each year for fund expenses. According to Morningstar Inc., the average U.S. stock fund has an expense ratio of about 1.43%, which means you pay $14.30 per $1,000 invested. The average U.S. bond fund has an expense ratio of 1.04%.

Below, we give a breakdown of operating expenses that fund shareholders typically pay. Where possible, we've supplied averages you can use to compare your fund with its peers. We'll start with operational fees, which generally are taken out of the fund's returns before gains are passed on to investors. They include:

Management fees (0.5%-1% of the fund's assets annually). In a nutshell, this is the portfolio manager's fee, the amount the fund pays an advisor to manage its portfolio.

Marketing fees (up to 0.75% of a fund's assets). Known as 12b-1 fees in mutual fund jargon, marketing fees go to pay for marketing and advertising costs, and also to compensate selling agents.

But those aren't the only costs taken out of your fund money. The following fees are assessed on transactions, such as the purchase or sale of your shares in a fund:

Front-end sales charge (4%-8% of an investment). Commonly called a "load," a front-end sales charge is assessed on your purchase of mutual fund shares. It's paid to the financial planner or broker who steered you into the fund. Under the law, this charge can't exceed 8.5% of your initial investment, according to the Investment Company Institute. The disadvantage of a front-end sales charge is that it immediately reduces the amount of money that you put to work. Say you invest $5,000 in a fund with a 3% sales load. The broker takes his 3% cut--or $150--and you're left with an investment of $4,850. Our advice: choose your own funds and make sure they don't have a load.

Back-end sales charge (4%-8% of withdrawals). Back-end "loads" are paid when you take money out of a mutual fund or redeem your shares. Many in the mutual fund industry feel both front- and back-end loads keep investors disciplined, and prevent them from shuffling money in and out of the market. And while some mutual fund companies will waive either load, it comes at the price of keeping your money in the fund a set amount of time--say five years or more.

Contingent deferred sales charge (4%-8% of withdrawals). This again is another fee paid to financial professionals the minute you sell your shares. In contrast to traditional back-end sales loads, contingent deferred sales charges usually apply only for the first few years that you own a fund; then they disappear. That's why these charges are sometimes called short-term redemption fees. They're designed to discourage investors from bailing out of a fund soon after buying in.

Exchange fees (0.25%-1% of amounts moved). This charge is levied by some mutual funds when you transfer money from one fund to another within the same mutual fund family.

Maintenance fees ($10-$50 annually). Once your balance falls below a certain minimum, many funds will assess you a maintenance fee. Many funds also charge a yearly custodial fee to cover the administrative costs of handling an individual retirement account.

Michelle A. Smith, managing director of the Kansas City, Missouri-based Mutual Fund Education Alliance, says it's imperative you go over fund expenses the next time you shop for investments. "It's absolutely necessary if you intend to get the whole picture," she adds. "Don't just leap at performance numbers, do some digging."