Stone Soup

My ketchup has been in the fridge almost a year. Is it still good? How long can I keep the mayonnaise once it is opened? Do I have to keep mustard in the fridge? Is that yogurt I stocked up on because it was on sale still good a week past the expiry date? My sons come over and check the expiry dates on things in my fridge, probably because they don't trust my judgment. Well here is a site that knows when things should be tossed.