Depends on whether you are buying a base or making your own. Also if using a base are you adding more than just f/o. How sterile is your work environment what containers are you putting it in. Are they sterile too? Usually bases will last anywhere from 6 months up to a year baring no nasties or germies have gotten into them when prepping. If you make it yourself I do not know. Depends if you use preservatives and again sterile working environment. You do not have to put a use by date on them no at least not that I am aware of.