Choices: It's or It's been? When to use which?

Question

It's three years since I last went to the cinema.

or

It's been three years since I last went to the cinema.

I chose It's been because I think this is an action which started in the past and continues in the present. Moreover, since usually goes with Present Perfect. This maybe my confusion, but whenever I see since, I automatically get Present Perfect.

(https://www.ef.com/english-resources/english-grammar/present-perfect/)

However, my teacher got It's as there's a formula like It is + time + since. But I got very confused as I don't know when to use which?

As I searched in https://dictionary.cambridge.org/grammar/british-grammar/linking-words-and-expressions/since, it seems that both is correct. But which would you as a native speaker often use?

Answer 1

It’s a long time since

In British English, present and past tenses are common in the structure It is/ was since It’s a long time since the last meeting. It was ages since that wonderful holiday. American English prefers perfect tenses in this structure. It’s been a long time since the last meeting. It had been ages since that wonderful vacation.

Answer 2

Technically, "it's" is a contraction of "it is". However, preceding "been" "it's" is used colloquially to mean "it has".

"It is three years since I last went to the cinema." No.

"It has been three years since I last went to the cinema." Yes.

So, "It's been three years ..." is the way to go, assuming your audience will accept "it's been" as "it has been". Writing out "It has been three years ..." is awkward. That's just not the way people speak.

But if you're in an English class, your instructor might not like it. In which case, go with "It has been ..."

Re: "both is correct" - when you use both, you say "both are", because "both" is plural; however, in this case, you don't want to use "both", you want to use "each" or "either" That is, "it seems that each is correct" or "it seems that either is correct"

I believe you're correct about the use of Present Perfect. As a native speaker, I can tell you that I know no one who knows the names of the tenses and/or the rules for their use. We pretty much just go with whatever comes out of our mouths. As a matter of habit, it's usually correct. But there are very many times when no one, even teachers, know the correct way to express something. English is a terrible language that way.