The direkt translation would be "one day more is one day less" However I haven't heard this expression in english before so I'm not sure if it's correct idiomaticly. It can express the similar message as "is the glass half full or half empty?" A person in jail could say one day less or one day more depending on their outlook on their time. Either you count down days untill your release(one day less) or you count the days you have been in prison(one day more)

"one day more is one day less" but in english people would not understand it.

Is this sort of a spanish proverb ? It means that when you live one day more it seems like adding one day to your life while it is substracting one day of your life as whole . So while we live one day more , we are aging and to our total living days we are living one day less ,got it ? It doesnt mean the same as the glass half full or empty,that one expresses how you see things from two different perspectives .Positive and negative , advantages and disadvantages of a situation ,, If you are optimistic you would look at the good side ( full half) and if pessimistic you ll just see the bad side ( empty half).