It is a very confusing concept, when to use "will" or "be going to". Both of them refer to the future but there is a slight difference. One of the differences that I have found and I was confused about is that:

We use be going to:

when there are definite signs that something is going to happen (we are sure, we feel it must happen).

Example: "I think it is going to rain. I just felt a drop."

We use will:

when we think or believe something about the future.

Example: "I think it will rain later so take an umbrella with you."

But when we use "be going to" in a sentence like this:

  • "Look at the clouds! It is going to rain."

why can't we use "will" since I don't think that in the last sentence we're sure, we are just making a prediction?

  • 2
    Don't "over-analyse" based on one perspective. It's not even particularly true that we're more likely to use going to when we're sure about what's going to happen. As a general "rule of thumb", you can think of will and be going to as interchangeable. It's just that the latter (which always include a present tense form of to be) can sometimes be seen as drawing attention to the relationship between what you see/think now and what this will lead to in the future (this now, therefore that later). Oct 24, 2014 at 15:20
  • Does this mean I can replace will or be going to wherever I want?when we have exams we have to be sure about the answer. Look at this sentence:can I use will or be going to:we should continue walking. It will/is going to get dark soon. Give me a clear explanation.
    – Katherine
    Oct 24, 2014 at 16:04
  • 1
    In most contexts the difference (if any) is so subtle I think it's unlikely you'd be tested on that particular aspect of English. IMHO the only useful way to look at it is "Is there any good reason for introducing the present moment (is going to) when talking about the future?". If not, stick to "simple future" will because it's, well, simpler. You may find this helpful. Oct 24, 2014 at 16:53
  • The ESL questions making you decide between is going to and will are very misleading; at least half the time, native speakers could use either one. There are some situations where native English speakers are more likely to use one or the other (e.g., it's going to get dark soon" is more likely, in your example.) But if all you care about is being understood, they're almost completely interchangeable. Oct 24, 2014 at 17:38
  • Yeah!! I answered it going to but my teacher said it is wrong because we feel it must happen but I still believe that it is be going to. I'm really confused:( and unfortunately, I have a test.
    – Katherine
    Oct 24, 2014 at 17:50

5 Answers 5


Simplified, you use the "will"-future if your prediction is based on calculation of data. You use the "going to"-future if your assumption is based on what you're actually seeing.

An example:
You see that a car is driving very fast and approaching a sharp turn, you say that there is going to be an accident.
However, when you know that once in a month an accident happens at a dangerous turn and no accident has happened this month so far, you say that there will be an accident soon.

The first one is based on what you see, the second is based on data.

Back to your example, the weather forecast predicts that it will rain tomorrow. This is based on data. But when you actually see dark clouds, you are very certain that it is going to rain.

In practice, however, there's always a blurry overlap and you can often justify both future tenses, especially when talking about the weather.

And unrelated to your choice, there's always a chance that it won't happen / is not going to happen.


"will"or the shortened "ll" is very short and has no weight at all whereas "to be going to do" is a long formula and automatically has a lot of weight.

Instead of fine and complicated analyses for when to use will-future (wF) and when going-future (gF) you can simply say you use gF when you want to give your idea weight and that is when you give a prognosis or when you tell someone something that is new for him.


“Is going to” is formally “Future simple”. In fact it uses present continuous tense to describe an ongoing process which just happens to refer to a future event. Read as “The weather is preparing right now for a future rain”.

“Will” is also future simple and formally equivalent to “Is going to”, but in fact it is a simpler construction and also derives from the concept of “will”, which has the air of inevitability around it.


First, you have to understand the meaning of the words, the essence of those words can tell you what you are saying if you can mix them with the grammar rules, and be successful in your enterprise.

Will according to the dictionary "used to express desire, choice, willingness, consent, or in negative constructions refusal.

Now the modal "will" as any modal is going to modify your main verb e.g. without modals; I run — with modals; I should run, I could run, I would run, I may run, I might run, and I will run.

Now that we understand that will is the willingness that a person has to do something, modify your verb and project that willingness into the future as a fact, a reality that will happen in the future. I have the intention of doing something in the future and I project that as a fact, a future statement, now you're not just expressing willingness anymore, you are projecting it as a fact a future reality.

Next, you have to understand that there is no such thing as a certain future, you cannot see into the future, but you can predict the future, in here the grammar rules are very important.

Will like we said before, is the a future statement of doing something but you are basing this statement in the will power, the willingness, the belief, the mere positive thought or idea, the feeling you have, the hunch that something is going to happen, meanwhile "be going to" is using present continuous because it is based on facts, real evidence that you have at hand, and has a higher probability that the action is going to happen.

According to the grammar rules "be going to" is used for a near future, reason; the near future has a higher probability of happening. "Will" is used for the distant future because has a lower probability of happening given that a lot of thing that you can´t prevent or foresee may happen.

"Will" is also used for improvised answers given the fact that in the moment you have the willingness of doing that action and that´s what you are expressing, you are proyecting that willingnes to do the action as a future fact or future statement into the inmediate future, in theory you don´t have the time to think in the facts, you only have the intention, backed up by your emotion.

That is how this thing supposed to be used, but in reality there´s a very thin line between these two words because expressing the percentage of certainty every time you talk is difficult itself and then there´s no one that can tell you the accepted measurement of percentage according to what you are feeling, that´s why you can exchange one for the other, it´s easier than think every time you want to express something in the future "Am I 90% sure that this is going to happen?" If you have to decide because they ask you to do it or you have the need of using this information, do it, if not, don´t do it, your choice, either way any word is accepted, this is just general useless knowledge, but in this case knowledge that can help you with your problem, and if you have the question about if it's possible that things can have the willingness to do something like the word it will rain, study the linking (Non-action verbs) VS the action verbs. Or save yourself the lesson and understand that as this, you are projecting your probability (The feeling we talked about before) in an inanimate object, (The probability you expect from that inanimate object to "do" the action "based on facts or just a hunch?").

I hope that you can find this useless information useful, I will leave you with a saying to think about, In my time Grammar wasn't a waste of time, but nowadays Grammar is a time of waste, isn't it?


"I am going to" is, as we know, the near future tense. By default, it speaks with a bit more confidence, but only because it is the near future. "I will" is just as confident but this form can also apply to a very far future, which reduces its certainty of happening in the near future.

Ejemplo: "Earth will explode" is almost a guarantee because entropy and general universal laws and the luck humanity has, but it says with no confidence that this'll happen soon. "Earth is going to explode", on the other hand, makes the thing seem a bit more tense. On the hypothetical third hand, there is no real difference between the two in terms of certainty.

With that general 'this is what the language really does spoken by people who learned it as babies' out of the way, we go through each of your examples:

"I think it is going to rain. I just felt a drop." Aye, seems certain, but that is because of the second sentence. "I think it is going to rain" is now much less certain, and if we drop the 'I think', we're left with "It is going to rain" which is certain. The certainty is defined not by the form but by the context.

"I think it will rain later so take an umbrella with you." Drop the 'I think' and the statement becomes certain. Again, context. Only.

"Look at the clouds! It is going to rain." Yes, it's a prediction, which by your rules demands a 'will' as opposed to a 'is going to' but the forms are picked primarily due to timing: it is going to rain in the near future, hence near future tense.


Don't pick the form based on certainty. If you want to introduce a belief, just prefix it with 'I think'. If you want to introduce certainty, back up your claim with an exclamation at how dark the clouds have got in the last few moments. Pick the form based on timing, where 'is going to' is near future and 'will' is everything after it.


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