"whenever" is often used for a one-time event which is expected to happen, but "every time" is not. More examples: Whenever you're ready to join the club, just give me a call. Every time she gets a headache she stays home from work! This is habitual behavior - recurring.

"Every time I look at the computer, the price goes up!" "Whenever I look at the computer, the price goes up!" In these two sentences, "every time" and "whenever" have the same meaning. You can use either one. "Call me every time you get off work." "Call me whenever you get off work." Depending on the context, these two sentences could have the same meaning. When I read them though, my first thought is that they are different. "Call me every time you get off work." This sounds like the speaker is telling the listener to call him every day at the time she gets off work. "Call me whenever you get off work." This sentence could mean the same thing as the other one. However, it could also mean that the speaker wants the listener to call him at the time she gets off work, but he doesn't know what time that will be. For example, let's imagine the speaker and listener are talking on the phone: A: "Hi! How are you?" B: "I'm very busy. I can't talk." A: "At 5:00 you'll get off work. Can I call you at that time?" B: "I don't think so. I might have to work late." A: "Can we talk at 6:00?" B: "Maybe. I don't know whether my work will be finished." A: "OK, then. Call me whenever you get off work." Because A doesn't know when B will get off work, he says "whenever." He could also say "call me when you get off work," but using "whenever" instead of "when" gives it a sense of uncertainty. Does that make sense?