Borrowers beware: Just because a bank is advertising a low mortgage rate doesn't mean that's the rate you're going to get. Tara Lynn Wagner filed the following report.

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It's a phrase we seem to keep hearing: mortgage rates are at historic lows! And just when you think they've hit rock bottom, they dip a little further.

"The rates are more like 3-and-a-half (percent) than 3.95," says Michael Moskowitz, the president of Equity Now. "The rates are really, really low."

But unfortunately, they aren't low for everyone. In fact, Moskowitz estimates that only 25 to 45 percent of borrowers get the best rate out there. Whether or not you're one of them depends on a number of things - a number of numbers, to be exact. The first is, of course, your credit score.

"In 98 percent of the cases, you need at least 620 or better," Moskowitz says. "The good rates start at at least 660 scores."

The second factor is your LTV, which stands for Loan to Value. Simply put, that's the amount of money you are borrowing compared to the appraised value of the home. A $200,000 loan on a $400,000 house would give you a 50 percent loan to value and likely a very good mortgage rate.

"It's really risk-based pricing," Moskowitz says. "The higher the credit score and the lower the loan to value, the better the rate you are going to get."

In addition to these stricter lending practices, Moskowitz says the other hurdle borrowers face is higher scrutiny.

"Five years ago, you got a mortgage, you sent in your W2, two pay stubs," he says. "That was it. Today, in every case, we get a copy of your tax return from your government."

That means access to a lot more information like deductions, unreimbursed business expenses and other adjustments that reduce your gross income and could reduce your ability to borrow the amount you need.

Moskowitz's advice? Being open and honest with your lender from day one will save everyone a lot of time and trouble.

"On the tax return, we are going to ask about everything," he says. "On the credit report, we are going to ask about everything. And don't think you won't be asked and you will get away with something because you won't. It's to your benefit to work with a lender up front. Up front is always better."

His other suggestion is to clean up your credit as much as possible. Raising your score even a little could lower your mortgage payments as much as $50 a month. That's $18,000 over 30 years.