Depends how you got it hooked up. Remember if your drawing alot of power off one circuit your meter will spin faster. You will see it make loops and spinning uneven. My power only went up about $25 give or take $10 from a 400w mh. I live in a small house though ive never seen a bill over $200. I also have a buddy that has a house a little bigger then mine using the same light he saw $60 increase. Anything will make your power bill go up leaving tv's on everythingso how much does a 400 watt hps cost to run???