Spanish gives you two main ways to talk about the future: the simple future tense (iré) and the near future construction (voy a ir). Both mean "I will go," but they work differently and sound different depending on the context.
The simple future tense, like iré (I will go), is a single conjugated verb. The near future, voy a ir (I am going to go), is a helper verb (voy) plus an infinitive (ir). In a sentence like "Tomorrow I will go to the mountains," the simple future iré fits because the question asks for a single word that means "I will go." This is the form you need: yo iré.
When you see irás, that is the second person singular (tú): you will go. That is a different person entirely, so it would not work for a sentence about yourself.
When do Spanish speakers use the simple future (iré)?
The simple future works when you are certain about something or announcing a plan with confidence. It sounds more formal, more decisive. You might say "Iré al médico el próximo martes" (I will go to the doctor next Tuesday) when you have already decided and booked an appointment. It is the tense you would use in a written announcement, in a promise, or when speaking about the distant future.
When do Spanish speakers use the near future (voy a ir)?
The near future, voy a ir, is what people actually say most of the time in conversation. It sounds more casual and immediate. If a friend asks "Do you want to come to the movies tonight?" you might answer "Sí, voy a ir" (Yes, I am going to go). The near future feels like something is about to happen or something you have just decided. Both forms are correct, but voy a ir is more common in everyday Spanish.
Why does this matter when you are learning
The difference is small but real. In a test or a fill-in-the-blank question, you need to know which form the sentence is asking for. If it says "Complete this sentence with one word," then iré is the answer because it is one conjugated verb. But in real conversation, you can use both forms and native speakers will understand you perfectly. The key is getting comfortable with how each one sounds and feels, so you can use them naturally when speaking.
The best way to make this automatic is to practise speaking with native speakers, not just reading grammar rules. When you spend time in actual conversation, you hear how real Spanish speakers choose between these forms in real time. You start to feel which one fits the moment. PBC Languages offers free language exchanges (called tandems) with native Spanish speakers, and you can also join small group classes with maximum four students. In a group that small, you actually speak every minute, not just listen. You get to ask a native speaker "Why did you use iré there instead of voy a ir?" and hear the answer in context. The connection between you and that person, the back-and-forth of real dialogue, is what locks in grammar like this. Your first class at PBC Languages is free, so you can try it and see how speaking practice with native speakers works.
Practice makes the future tense real
You can memorize conjugation charts, but you forget them. You can watch grammar videos, but they do not stick the way conversation does. When you speak the simple future out loud to a real person, when you have to choose in the moment whether to say iré or voy a ir because someone is waiting for your answer, that is when it becomes part of how you think in Spanish. Show up to small group classes or language exchanges regularly, and these patterns embed themselves without effort.