how long have you had the supplements, and how have you stored them? (in detail)
vitamins will degrade over time like anything else, faster with exposure to moisture, heat, and light. if you got them recently or aren't sure of how they've been stored, the only safe thing is to toss them and replace soon.
if you've had them for a long time and always stored them properly, they could probably go months to maybe a year or more before they're actually "bad".
I'm a biochemist and I work in drug development; the expiration date is kind of an imaginary number in some ways. but in others it's critical. if you're not sure, just toss it but make sure whatever you buy has a nice long time before expiration and store it carefully.