Believe it or not, nail polish does not go bad. Now we know we've been adamant before about getting rid of those beauty products when they expire. However, this is one that you can keep until it dries up or gets goopy on you.
Most cosmetics do not have strong enough preservatives to ward off bacteria for more than few months. Polish on the other hand is too potent for bacteria to survive in, no matter how long you've had the bottle. Just check out the big ingredients on your bottle – Ethyle Acetate, butyle acetate, nitrocellulose, Formaldehyde resin, isopropyl alcohol?! We don't know what a lot of these mean but they sure sound a little scary to be engulfed in if we were a little bacteria.
There is a downside to this product though. It can dry/goop up if you don't screw on the lid tightly enough. The same ingredients we just mentioned will evaporate and the polish will go to crap, if you will. Once it's dried up, then you will need to toss it.