Mortgage rates are volatile. Rate locks can offer peace of mind, but the decision to lock your rate is a bit of a gamble. Lock in too early, and you might miss the opportunity for a better rate.   Rate locks often last from 30 days to 60 days, though they sometimes last 120 days. Some lenders offer a free rate lock for a specified period.   A longer rate lock tends to be more expensive. For example, a borrower who chooses a 30-day lock on a fixed-rate 30-year loan might pay a 4 percent rate and zero points, while a 60-day lock might cost 1 point (equal to 1 percent of the loan) or a slightly higher rate with a half-point.   However, when mortgage rates are rising, you might consider locking the lower rate as soon as possible. It’s hard to time this decision perfectly, because no one really knows what interest rates are going to do.