Refinancing requires a new loan, and you'll want to be sure you "break even" by covering the closing costs and fees when you refinance. Since the terms and conditions of every mortgage loan are different, there's no set break-even period that applies to every mortgage refinance.
To calculate this, add up the refinancing costs that can include bank fees, title search and insurance costs, appraisal, attorney fees and credit check costs. Divide this total by your estimated monthly savings to determine how many months it will take to break even.
Total costs to refinance / Total monthly savings = # months it will take you to break even