A home loan is the biggest debt, and most costly monthly bill, most of us ever have.

That's why the seven biggest mistakes borrowers make when shopping for a mortgage can cost so much money and aggravation. Avoid them, and you're a much happier and smarter home buyer.

Mistake 1. Not shopping around for the best deal.

Getting the right loan, with the lowest possible interest rate and reasonable fees, can save hundreds of dollars a month and tens of thousands of dollars over the life of the mortgage. But you'll never know whether you got a great rate if you only get one quote from the bank down the street or the mortgage broker that arranged your last loan.

Our extensive database of mortgage rates can give you a good sense of what loans cost right now. Follow our step-by-step advice on how to find the best interest rate and home loan.

Mistake 2. Applying for a loan without checking your credit history for mistakes.

Errors can drive down your credit score and make it more difficult to qualify for a loan and require you to pay a higher interest rate. To get a free credit report from the three major credit reporting bureaus, go to www.annualcreditreport.com.

Each credit report shows how to correct mistakes or submit an explanation for legitimate black marks that appear on the report.

Mistake 3. Saddling yourself with payments you can't afford.

Avoid that by looking at all of your bills and deciding how much you can comfortably spend. Include a realistic estimate for taxes, insurance and condo or association fees. From that, calculate the amount that could be borrowed at prevailing mortgage interest rates. Add the size of the down payment and that should be your limit.

Don't let real estate agents repeatedly show you homes outside this price range. Don't work with mortgage brokers who push you to borrow more than you can afford. Here's more help on deciding how much to spend on a home.

Mistake 4. Failing to understand how costly home maintenance can be.

Just because you can keep up with the mortgage payments doesn't mean you can afford a house. You don't want to find out how expensive home repairs can be when your central air conditioning conks out, the dishwasher spews four inches of hot, soapy water on your kitchen floor or the roof starts to leak.

This is especially important if you're buying your first home. You can't call the landlord. You have to call repairmen, and they don't come cheap.

The Federal Housing Administration says you should plan on spending the equivalent of one mortgage payment a year on repairs. You'll also have to buy lawn mowers, snow blowers (if you live far enough north), ladders, tools and other stuff you don't need as a renter.

Mistake 5. Not getting preapproved for a loan.

This is an important reality check -- and it's free. A lender will look at your credit history, income, savings and debts, and decide on a loan cap, though you don't have to borrow the entire amount. If you can't get preapproved, or can't get preapproved for as much as you want to borrow, that's a big red flag. Our report will help you learn all about getting preapproved.

Mistake 6. Signing a mortgage that you don't understand.

A recent study revealed that two out of every five homeowners didn't know whether their mortgage had a fixed or adjustable rate. And if it had an adjustable rate, they didn't know when it would adjust or what their payments would be after the adjustment.

The best place to find most of a loan's key terms is the "Good Faith Estimate" lenders must provide within three days of receiving your application. Knowing the answers to the 10 questions your GFE should answer will greatly reduce the odds for a nasty, costly surprise.

Mistake 7. Not considering a five-year, adjustable-rate mortgage.

Costly subprime mortgages have given all ARMs a bad name. Lenders have shied away from making them. Borrowers have been scared to even consider them. That's why more than nine out of every 10 mortgages written this year have been fixed-rate loans. But there's nothing wrong with the consumer-friendly ARMs usually given to borrowers with good credit. They're a particularly smart idea for borrowers who know they'll be moving before their loan adjusts in five, seven or even 10 years.

At today's rates, those ARMs cost about $30 to $40 a month less than a 30-year, fixed-rate mortgage for every $100,000 you borrow.

By the editors of Interest.com

Have questions about your finances? Ask us at editors@interest.com.

Whether you're buying a home or refinancing an existing mortgage, we have a mortgage calculator that can help you make the right decisions.