It is feasible to go for a refinance when you have built up at least 10% equity in your home (For Fannie Mae owned mortgages, the value is 5%). It is also possible for you to choose the option if your equity is less than 5%, but you may have to pay a certain amount of cash in order to make up for the difference in equity.
When refinancing a mortgage, as many as 30% of homeowner's cash out part or all of their home's equity. By investing in home improvements or paying off credit cards, this can be a smart. But, if you are borrowing more than 80% of your home's value, you will be hit with private mortgage insurance, costing you hundreds a year.
If you want to make sure the interest rate your lender offers you is the rate you get when you close the loan, ask about a mortgage lock-in (also called a rate lock or rate commitment). Any lock-in promise should be in writing. Make sure your lender explains any costs or obligations before you sign.
Ask the lender or broker for a comparison of the up-front costs, principal, rate, and payments with and without this rate trade-off.