Mañana voy a presentar el formulario en la ventanilla.

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Breakdown of Mañana voy a presentar el formulario en la ventanilla.

• en: at
• ir: to go
• a: to

Questions & Answers about Mañana voy a presentar el formulario en la ventanilla.

Why is it voy a presentar instead of just presentaré?

Both are possible, but they are used a little differently.

• Voy a presentar is the ir a + infinitive future, very common in everyday spoken Spanish.
• Presentaré is the simple future, which can sound a bit more formal, more written, or sometimes less immediate.

In this sentence, Mañana voy a presentar el formulario... sounds very natural in conversation: Tomorrow I’m going to submit/hand in the form...

So:

• Mañana voy a presentar el formulario = very common, conversational
• Mañana presentaré el formulario = also correct, but slightly more formal or less colloquial

Why is mañana used without a preposition?

In Spanish, many time expressions do not need a preposition.

So you simply say:

• mañana = tomorrow
• hoy = today
• ayer = yesterday

That is different from some other time phrases, where Spanish may use a preposition:

• por la mañana = in the morning
• en mayo = in May
• a las tres = at three o’clock

In your sentence, mañana is just an adverb of time placed at the beginning for context.

Can I also say Voy a presentar el formulario mañana?