There is an unusual situation in English where the terms ‘have’ and ‘have got’ seem to have the same meaning in two contexts, as follows:
Context 1) I have a sister / I have got a sister = possession
Context 2) I have to do an exam tomorrow / I have got to do an exam tomorrow = obligation
Indeed, the two sentences in each context are interchangeable. So, despite ‘have’ being the verb (present simple tense) in context one (I have a sister / I have got a sister) while it is the auxiliary (present perfect tense) in the second two (I have got a sister / I have got to do an exam), the meaning is the same each time.
This can be difficult for learners of English to accept. Often, then, the question is ‘But when do you use ‘have’ and when do you use’ have got’?
The answer to that question can be equally as frustrating. ‘Whenever you want’. Indeed, there is no reason why a native speaker would say one rather than the other, other than perhaps personal or regional habit.
It is the same in questions:
‘Do you have a sister?’
‘Have you got a sister?’
These questions ask for exactly the same information, but it can difficult to accept that there are two such different grammatical structures to elicit the same information. But, once again, the two questions do indeed have the same meaning.
When ‘have’ and ‘have got’ are not the same
Of course, in cases of language, there usually are some exceptions. But in English, the difference between ‘have’ and ‘have got’ really comes down to what is and isn’t possible with both grammatical structures.
‘Have’, as a simple verb (without an auxiliary), can be used in any grammatical tense, other than in continuous form (because it is a stative verb, not an action). Therefore:
‘I have a dog.’ (now)
‘I had a dog.’ (in the past)
‘I will have a dog.’ / ‘I’m going to have a dog.’ (in the future)
It is the same with obligation:
‘I have to do some work.’ (now)
‘I had to do some work.’ (past)
‘I will have to do some work.’ / I’m going to have to do some work.’ (in the future)
Because ‘have got’ is technically a present perfect structure (‘have’ is the auxiliary’, ‘got’ is the verb), it cannot be adapted into any other verb tense.
‘I have got a dog.’ (now)
‘I had got a dog.’(past) ‘I will have got a dog.’ / ‘I’m going to have got a dog.’(in the future) – possible, but changes meaning.
It’s the same with obligation:
‘I have got to do some work.’ (now)
‘I had got to do some work.’(past) ‘I will have got to do some work.’ / ‘I’m going to have got to do some work.’(in the future)
‘have’ as another verb
‘Have’ is a verb with multiple meaning in English. For example:
‘I have lunch at 2pm.’ (eat)
‘I’m having a coffee.’ (drinking)
‘I’m going to have a shower.’ (take)
‘Have got’ does not have the same meaning as ‘have’ in any of these other uses, so cannot be interchanged.
To reiterate, ‘have’ and ‘have got’ only have the same meaning when we talk about possession and obligation.
But the two forms can be only used interchangeably in the present simple tense. If any variation of tense is required (for past or future), then ‘have got’ cannot be used.