Which one to useA2

Will vs going to

The short answer

Ask when the decision was made. If you decided before you started speaking, use going to. If you are deciding as you speak, use will. Going to also covers predictions with visible evidence: those clouds mean it’s going to rain, while will covers opinions about the future.

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At a glance

Will or Going to?

CompareWillDecided now, or an opinion about the future.Going toDecided already, or evidence you can see.
When you decidedAs you speakBefore you spoke
PredictionsBased on opinion: I think it’ll rainBased on evidence: look at those clouds
Offers and promisesI’ll help you, I’ll be thereNot used
Plans and intentionsNot usedWe’re going to move house
RefusalsThe car won’t startNot used
After if in a conditionalIn the result: I’ll call if I’m lateNot in the if half

How to choose

Ask these, in order

  1. 1

    Had you already decided before this conversation?

    Going to. It reports an existing intention rather than forming one.

    We’re going to redecorate the kitchen in spring.

    The plan already exists.

  2. 2

    Are you deciding right now, in response to what was just said?

    Will. This covers offers, promises and on-the-spot choices.

    We’ve run out of milk. I’ll get some.

    The decision is made in the moment of speaking.

    NB“I’m going to get some” would mean you had already planned to.

  3. 3

    Can you point at evidence for the prediction?

    Going to. Something visible now makes the outcome look inevitable.

    Slow down / you’re going to hit that kerb.

    The evidence is in front of you.

  4. 4

    Is it an opinion, expectation or guess about the future?

    Will, usually with think, expect, probably or I’m sure.

    I think she’ll like it.

    An opinion, with nothing to point at.

Side by side

Each one, in full

Will

When to use will

Decided now, or an opinion about the future.

Will forms the future at the moment of speaking. That covers instant decisions, offers, promises and refusals, and it is why “I’ll” appears so often in dialogue and so rarely in a written plan.

It also carries opinions about the future: predictions with no evidence behind them, usually attached to think, expect, hope, probably or I’m sure. And it is the form used in the result half of a first conditional.

That looks heavy, I’ll give you a hand.

An offer, decided on the spot.

I expect they’ll be late again.

An opinion, not evidence.

The printer won’t turn on.

A refusal, the machine will not cooperate.

NBWon’t means refuses here, not simply “does not”, which is why it sounds slightly exasperated.

Going to

When to use going to

Decided already, or evidence you can see.

Going to reports a decision already taken. If the plan existed before the conversation started, this is the form, however far off the event is: going to is about the state of the decision, not the distance in time.

Its second job is prediction from present evidence. Something visible now points at the outcome: the sky, the score, the way someone is driving. That is what separates it from will, which predicts from opinion.

She’s going to study medicine.

Decided, and probably applied for.

It’s going to be a long meeting.

You can see the agenda.

I’m going to tell him tonight.

A decision made earlier today.

NB“I’ll tell him tonight” would suggest you have only just resolved to.

Mistakes to avoid

What learners actually get wrong

  • I will visit my parents next weekend, it’s been arranged for a month.

    I’m going to visit my parents next weekend.

    An arrangement made in advance takes going to. Will suggests you decided while speaking, so it quietly contradicts the fact that the plan is a month old.

  • If it will rain, we’ll cancel.

    If it rains, we’ll cancel.

    The if half of a first conditional takes the present simple, however clearly future the meaning is. Will belongs only in the result half.

  • The phone’s ringing. I’m going to answer it.

    The phone’s ringing. I’ll answer it.

    The decision is being made in response to the ringing, so it is will. Going to would imply you had been planning to answer that particular call.

  • Look at the traffic. We will be late.

    Look at the traffic, we’re going to be late.

    You are pointing at evidence, which is going to. Will works for a prediction with nothing behind it, but here the sentence has just supplied the reason.

Now use it

will vs going to

Decisions, predictions and plans: choose the future that fits. Reading a rule and being able to apply it are different skills, and only one of them shows up when you speak.

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Questions

Asked and answered

Is one of them more correct or more formal?
Neither. Will is not more formal than going to. It is more immediate. Written English uses will more often simply because writing contains more predictions and fewer instant decisions, but going to appears in formal writing without any awkwardness.
Where does the present continuous fit?
It overlaps heavily with going to for arrangements, and is often the more natural choice when another person is involved: I’m meeting Sara at six. Going to is closer to intention, the continuous closer to a fixed arrangement, and in practice they are interchangeable in many sentences.
Is gonna acceptable?
In speech, universally. It is how going to is normally pronounced, in every register including newsreading. In writing it marks casual or reported speech, so keep it out of anything formal, and never write it in an exam.