Yes, it is possible to refi without paying anything but you make up for it in the interest rate. If you want the lowest rate available to you, then it would entail paying closing costs. Right now, most rates are around 4.875% and there may be a slight discount fee on that epending on the day. I would advise you to take the lowest rate available simply because rates like this may not be back around for a while.
If you have a conventional or FHA loan, there is not a prepayment penalty and you can technically refi 1 day after being on title. However, please note that the loan officer that did your current mortgage might be expensed a fee from the lender - not you. Lenders put stipulations on their loan officers as a means to prevent them from refinancing the same customer over and over. This protects the customer at the same time.
I would say that any rate greater than a 1% difference of what you have now would be a great advantage of you to take. Yes, it may take a year or 2 to recoup the costs of the refi vs. your monthly savings but if you are taking this new loan for the long term, then I would say that it will be a great investment.
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