Both WILL and GOING TO refer to the future, though there are subtle differences between the two. Read on to understand the differences better.
When To Use Will:
• For actions that we decide to do right now / at the moment of speaking (rapid decisions)
I haven't spoken to Tom in a while. I think I'll give him a call.
• When we think or believe something about the future (prediction) based on feelings or instincts.
In 2050, students will travel to the Moon on field trips.
• To make an offer, a promise or a threat.
I'll give you a discount if you buy it right now!
• Use WON'T when someone refuses to do something.
Marta won't go to work even though she may get fired!
• To express a wish in the distant future.
Someday, I will learn Italian.
• WILL structure: Will + base verb in infinitive.
Example: I will buy a house someday.
When to use GOING TO:
• The decision has already been made before the moment of speaking / preplanned decisions.
They are going to retire to Florida - they have already bought their condo!
• When there are definite signs that something will happen / when something is guaranteed to happen.
I don't feel well. I'm going to throw up.
• When something is just about to happen / immediate future.
Stay back! The roof is going to fall in!
• GOING TO structure: am / is / are + GOING TO + base verb in infinitive
Example: I'm going to London in summer, I've already got the tickets!
Comparing WILL and GOING TO:
What plans do you have for this evening?
I'm going to the cinema, and you?
Not much. Maybe I'll watch TV
• Jane uses GOING TO as it is a preplanned event, a decision made ahead of time. In this case, she can't use WILL.
• a spontaneous decision that Tom is not sure of, an impulsive decision, an uncertain event in the future.
We hope that clears it up!
Here is the great news - in most cases, WILL and GOING TO can be used interchangeably, without a big change in meaning, so no one will have trouble understanding you!