The must be 40% of your lash extension still on be considered a fill. Anything less or anything after 43 weeks is considered 3 weeks refill after 3 weeks considered full 4 weeks set. Fills are touchup appointments to add extension to lashes that have shed and new lashes that have grown. Prices are based on time. The better you care for your lashes, the less time you will need. Make sure to come to your lash appointment with out any eye makeup to maximize the time we can apply lashes .