NEW YORK (MainStreet) — It's a common rationalization: "I'll get the best mortgage I can now and refinance later if things change." A few years down the road, mortgage rates might be lower, or you might want to take some cash out of your home for something else. Refinancing can be a second bite of the apple.

But don't count on it. Homeowners who think refinancing will be a breeze often find the doors slammed in their faces. The mortgage you get today may be the one you're stuck with.

Despite historically low mortgage rates in the past few years, about half of mortgage holders have not refinanced, staying with older loans that cost more — typically 6% or more when a refinancing could have cut the rate to below 4%, according to a survey by Fannie Mae.

The mortgage-backing company recently polled 1,327 homeowners with mortgages to find out why so many had not refinanced. Among the reasons cited by borrowers most often: not being able to reduce payments enough, feeling that closing costs were too high and not wanting to commit to additional years of payments.

Many homeowners reported they had been rejected for refinancing. Many simply did not qualify for refinancing even though they obviously had qualified for a mortgage before. Even though a new loan at a lower rate should have a lower payment, making qualifying easier, the borrower's credit rating may have slipped, or one spouse's job loss would reduce the household income below what was required.

The homeowners who had not refinanced tended to be first-time homeowners and younger than others, and they had lower incomes and less education than those who had refinanced. Many cited the costs of refinancing as a serious obstacle. And some said they were underwater — owing more than their homes were worth after the housing collapse — and could not come up with enough cash to pay off their existing mortgages.

The study found that homeowners are unlikely to refinance during the first six years in the home, and that the "prime time" for refinancing is from years six to 15.

Bottom line: Get a mortgage only if you can live with it for the duration. Don't count on getting a lower rate later — especially as rates are more likely to go up than down over the next few years. And don't assume you'll be able to take cash out of your home. Even if rates are appealing some years from now, qualifying for a loan is never guaranteed. And you can't be sure the home will appreciate enough to provide much equity, or value in excess of any loan balance. Building equity the other way, by trimming the balance through regular payments, is a slow process.

Before getting a mortgage, get a little perspective on refinancing issues by playing with the Refinance Break-even Calculator. It will show just what the conditions would have to be to make refinancing pay. You may find some of those factors, like a significant drop in loan rates, too much to count on.

--Written by Jeff Brown for MainStreet