That can vary depending on many factors. The quality of prebuilt factory assembled coils can be spotty. Some prebuilt coils are total duds. Coils are finicky things, and these companies make them by the millions. Just open up a few prebuilt heads some time, and you will see that the quality of the coils is not consistent. In Kangers defense, no companies are. And then it depends on the flavorings and vg/pg ratio of your juices, and how much you vape, and at what wattages. I build all of my own coils these days, but when I used to use prebuilts at around 30 watts, 3 mil of liquid a day, I could get around a month or two of use out of a good coil.