Summer has arrived with some cool mortgage rates

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Borrowing costs are at rock bottom, making this a great time to buy a home or refinance your existing home loan.

Today, you'll pay about 4% on average for a 30-year, fixed-rate loan.

Rates have dropped significantly since last summer -- the average mortgage then sold for 4.75% -- even as home sale prices have shown a slight year-over-year increase, according to the Federal Housing Finance Agency.

Our weekly chart of average mortgage rates shows what you can expect to pay for a typical loan in 25 major metropolitan areas.

Phoenix offers the cheapest 30-year loans on average at 3.79%, based on our late-May survey of lenders, while Tampa is the most expensive, with the average home loan going for 4.54%.

The information in our chart can guide you toward the cheapest home loans in your area. Search our extensive database to find the best rates from hundreds of lenders.

Your location, along with your creditworthiness, will influence your interest rate, but we’re seeing loans as cheap as 3.625% in several major metropolitan areas with no points and less than $2,000 in lender fees.

Our mortgage calculator will show you what your monthly principal and interest payments would be on any fixed-rate loan.

If you require a jumbo loan, the news is good for you, too, as these home loan rates are at record lows, as well.

Jumbo loans are loans larger than the limits on loans purchased by Fannie Mae and Freddie Mac, the two big government-owned companies that buy most of the mortgages issued by banks and other lenders

The upper limits on these loans vary by location but range from $417,000 in most places to $625,000 in the nation's most expensive cities. These limits adjust up or down annually as real estate prices fluctuate.

You can find the conforming loan limit for your county at the Federal Housing Finance Agency.

Loans under the limits are called "conforming loans," and the difference in price between jumbo and conforming loans has shrunk considerably.

If you want to borrow above these limits, you’ll need to apply for a jumbo loan. Like conforming loans, jumbo loans come in fixed- and adjustable-rate varieties. It’s also possible to get a jumbo FHA or VA loan.

But do you have what it takes to get approved for a jumbo loan?

Not being able to sell a loan to Fannie or Freddie increases the bank’s risk, says Richard Rector, vice president of business and private banking for Green Bank in The Woodlands, Texas.

That makes jumbo loans harder to qualify for and more expensive.

Expect to pay about half of a percentage point more for a jumbo loan, although rates can vary depending on other characteristics, says Peter Grabel, senior mortgage loan originator with Luxury Mortgage in Stamford, Conn.

Expect to put down a larger down payment, as well.

Then you've got to prove that you can make the substantial monthly payments of $3,000 to $5,000 that these loans require. You'll need to:

“In the current environment, we are seeing second- and third-level reviews by more than one underwriter, and this can result in additional conditions being asked for that are not on the initial approval,” says David Lazowski, branch manager at Fairway Independent Mortgage in Boston, Mass.

If you’re applying for a jumbo loan, mortgage broker and jumbo loan specialist Todd Huettner, president of Huettner Capital, offers these tips:

Work with a specialist. Little mistakes on big loans have big costs. You must work with a jumbo loan specialist to avoid surprises.

Look around. Loan guidelines vary greatly. You might not qualify with one lender, but be fine with another.

Shop your rate. Rates and fees vary greatly with jumbo loans, so check around.

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