Regarding this, what are you up to answer?
"What are you up to" is a very common and casual (informal) way of saying "What are you doing?" You may also hear people say "What's up?" which has the same implication. Your answer to this should be equally casual, as most people don't expect a long or detailed explanation of what you are doing.
Subsequently, question is, what are you up today? So, to answer your second question, it can mean, "what are your plans/what are you doing today", although it sounds more natural to use it when asking someone what he is doing right now.
Likewise, people ask, what are you up to meaning?
Originally Answered: What is the meaning of “What are you up to”? What are you up to is an idiom that means what are you doing? Such as when you ask someone what they are doing, you say, what are you up to? Or it can be used as, are you up to questionable behavior?
What you up to or what you up too?
” “Too” means 'also' as in “I am going to the movies too”. It can also mean to a higher degree than is desirable as in “You have put too much sugar in your tea”.