Most Helpful Girl
unopened, then it’s in the cupboard. if it’s open, you definitely need to put it in the fridge. it’s just like canned food.
Most Helpful Guy
If it is unopened, ketchup can either go in the cupboard/pantry or the fridge (if you want to pre-chill it). However, once you open it, it should go in the fridge. I believe that it probably also says "refrigerate after opening" on the bottle too.
Now, with that being said, it probably won't kill you if you keep it in the cupboard for a time period. (I. e. if you left it out overnight, you don't need to toss it). It's not like mayo or dairy products in that regard.