Learners' Questions: The Future: present continuous, be going to, will

Christina in Austria says: would you be able to explain the difference between "will" and "going to" when talking about the future please? I've heard a few explanations in the past but I'm still unsure about what to use a lot of the time.
Dan has the answer!
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Transcript
Dan
Hi guys! Dan for BBC Learning English here with this week's Learner Question. Find out what it is after this.
This week's learner question comes from Christina from Austria, who asks: Would you be able to explain the difference between "will" and "going to" when talking about the future, please?
Of course, Christina, it’s quite a common question. I hope this answer helps.
So, there’s a difference between future predictions and future plans and we’re only going to be looking at future plans for the moment. Please remember that these rules are a rough guide and sometimes native speakers bend or even break them – so be careful.
So, a man goes to the airport. He’s carrying a suitcase. In the suitcase is a passport, some clothes, some sunglasses and a ticket. He’s goes up to the check-in desk and he says to the lady there, “I’m flying to Spain later today.” Notice this is the present continuous. That’s for a future arrangement. It’s called an arrangement because it’s like a plan, but he has the ticket, and the ticket is evidence of the plan. This means that if the man were to disappear, the airline would still expect him to arrive for the flight. That’s what the evidence means.
However, the lady behind the check-in desk says “Sorry. No, that flight’s been cancelled. But you can fly to Australia or to Russia.” Well, this is a big decision, so the man goes to the cafe to think about it. When he comes back he says, “Ok, I’m going to fly to Australia.” That’s be going to for a future plan. He’s had time to think about it in the cafe before speaking, but he doesn’t have a ticket so it’s not an arrangement.
But the lady behind the check-in desk says “Sorry! You took too long in the cafe. That flight has gone. But you can still fly to Russia.” So, the man says, “Ok. I will fly to Russia.” That’s will for a future based on a decision made at the moment of speaking.” He makes the decision at that time. No plan existed before that.
Did you get it? That’s present continuous for a future arrangement. It’s be going to for a future plan and it’s will for an instant decision made at that moment.
I hope that answers your question Christina. Thank you very much for writing to us. If anybody else out there has a question for Learners’ Questions, you can email us on: [email protected]. Please remember to put Learners’ Questions in the subject box and your name and the country that you’re writing from. Unfortunately, we get so many emails that can’t every question, guys, but we do read every single one. And for more information, go to our website, bbclearningenglish.com. That’s it for this week’s Learners’ Questions. I’ll see you next time. Bye!