Most grammar and coursebooks will tell you that "Must" indicates a personal responsibility and that "Have to" indicates a sense of responsibility or duty to someone else. Consider these examples: l must stop smoking (because I personally think it would be a good thing to do), I have to stop smoking (because someone else, perhaps my Dr told me to do so). However, in practice you will find many speakers using them interchangeably with no difference in meaning.

Here is the answer I gave when a member asked this same question a few days ago: In many situations, they have the same - or very similar - meaning. For example, there is very little difference between 'I must go' and 'I have to go'. In some cases, 'have to' indicates an external obligation, while 'must' indicates an internal or self-imposed obligation, but this is not always the case. When we are talking about obligation, the 'have to' form is more common, because it is grammatically more flexible. The 'must' form is only used in the present tense. In all other tenses, you use 'have to' (I'll have to work, I had to work and so on). It also has no negative form (the negative of 'I must do this' is 'I don't have to do this') . Even the interrogative form of 'must' is rare - we tend to say 'Do I have to do this?' rather than 'Must I..?' Note that the form 'mustn't' means 'It is forbidden/not permitted''. If you want to express a lack of obligation, you say 'I don't have to'. It's also important to realise that 'must' has other meanings and uses which are different from 'have to'. If you say 'You must be tired', this means 'I presume that you are tired'. If you say 'I must have left my phone on the bus', you mean that you deduce that this is what happened. In fact, in the majority of cases, when a native speaker uses 'must' it is for an assumption or conjecture such as this, rather than as a synonym of 'have to.'

I can't think of a time when they will have different meanings. To some people using 'must' may seem more authoritative or proper. However, you can negate 'must' with not (mustn't) but it would be very awkward to try to negate 'have/has to' with 'not,' so people will instead generally default to "can't".

Thanks

there is no difference. Eg. I have to do y homework today / i must do my hombre he has to reach home early / he must reach home early They have to study everyday/ they must study everyday *However, i guess that at times one is more applicable in a context''