anytime vs whenever

anytime

• At any time 

• Suitable for any time; not associated with any particular time. 

• "you're welcome" in response to "thank you" or "thanks." 

whenever

• At any time. 

• When ever: emphatic form of when. 

• When. 

• Every time that. 

• At any time that. 

• Regardless of the time that. 

• At the (single) time that, no matter when.