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Questions & Answers about ¿Qué harás mañana?
Why use harás instead of vas a hacer?
Harás is the simple future tense of hacer (to do). While you can perfectly use vas a hacer (you are going to do) for upcoming plans, harás translates closely to "will you do". Both are very common and natural ways to ask about the future in Spain.
Why does the verb harás look so different from hacer?
Hacer is irregular in the future tense. For regular verbs, you add the future ending directly to the full infinitive (like comerás). But for hacer, the base changes to har-. Then you add the tú (informal "you") ending -ás to get harás.
Doesn't mañana mean "morning"?