With these two things, they can last a very long time:
#1 proper care (see aftercare instructions)
#2 touchup visits. Touch ups are necessary to maintain your eyelash extension because normally, a person's natural eyelash falls out every 60 - 90 days while and then a new one starts to grow in its place. Therefore, it is necessary to get touch-ups to fill in the fallen lashes. About every 2 - 3 weeks is recommended, however this will vary from person to person. Those who have a faster eyelash growth cycle may need a touch-up sooner, while those with a slower eyelash growth cycle may not need a touch-up as often. Your natural lash cycle as well as how you take care of your lashes will affect how long they last.