The longevity of wax melts varies depending on the brand, fragrance, and size of the melt. Generally, wax melts can last anywhere from a few hours to several days, depending on how often you use the warmer and how much wax you use at one time. You'll know it's time to change the wax melt when the fragrance starts to fade, or when the wax has completely melted. At that point, you can discard the wax and replace it with a fresh melt.