It really depends what type your taking, from Dr Gregor ” my professional opinion, the easiest and most inexpensive way to get one’s B12 is to take at least 2,500 mcg (µg) of cyanocobalamin once each week, ideally as a chewable, sublingual, or liquid supplement (you can’t take too much–all you get is expensive pee).
Or, if you’d rather get into the habit of taking something daily (instead of once-a-week), I recommend at least 250mcg (I know the math doesn’t “add up” but that’s due to the vagaries of the B12 receptor system”
Hope that helps 🙂