Over time oils can break down, becoming less effective, but they don't really expire. Some carrier oils will have an expiration date printed on the bottle but are usually good for at least several years. Essential oils never expire, though they can lose potency over time. When in doubt, run a smell test. If it smells off, dump it out and make a new batch. If you use this oil daily or even a few times a week, you should easily finish it before it goes bad.