It depends on whether you extract it directly from the plant or if you buy a packaged 100% gel. The packaged product usually contains preservatives (make sure it's only green preservatives like potassium sorbate) which means it'll last for a while. You can usually find an expiry date printed on the bottle. If you decide to make the extract yourself you have to make it fresh every time you use it. Other than that the plant will keep it fresh as long as you water it every once in a while.