Start by filling out this basic worksheet. If the numbers look favorable, then go to one of the website calculators in the Resources sidebar (right), to work up a more detailed evaluation. (If you plan on taking out a zero-cost refinancing loan, then skip immediately to a Web calculator.)

1. Current monthly payment
$___

2. New monthly payment (use the national average for a 30-year fixed rate listed in the newspaper or at www.hsh.com)
$___

3. Subtract 2 from 1
$___

4. Estimate your closing costs (typically 3 percent of the new loan)
$___

5. Divide 4 by 3 (this is number of months it will take to recoup your closing costs)
___

6. How many months do you plan to live in your home?
___

Line 6 should be at least 12 to 18 months more than the answer in line 5 for refinancing to be worthwhile.