No one really knows what is the shelf life of nailpolish. You don't see any expiration dates on the bottom of nail polishes or anything. How do I know if my nail polish is expired?
Texture
You can tell right away if the nail polish is expired thru its texture.
It will feel thick, clumpy and difficult to apply
How to preserve your nail polish
Your nail polish should last as long as you store it properly. Store it away from direct sunlight and in a cool, dark setting. Heat and light can cause some reactions that may degrade or cause the breakdown of the nail polish's formula.