Hey Ei. In English, we use the words must and have to when we want to say that something is to be done necessarily or compulsorily. Police have to arrest the criminals as soon as possible. Criminals must be life-sentenced. I went to meet the doctor, but he was not at the clinic. The receptionist said, “You have to wait, the doctor must be on the way.” Definition of Must The word ‘must’ is used to express the compulsion or inevitability of doing something according to the circumstances, which cannot be ignored. It can be used in the following ways: It indicates something which is absolutely necessary, to happen: Some corrections in the Project must be made. One must be influential, to become a leader. Candidate must be an expert in the subject, to apply for this job. You mustn’t be late for the exam. Definition of Have to: When someone is forced or bound to do something, we use the word ‘have to’. Hence, it denotes an obligation imposed on someone. Let’s discuss its uses with the help of examples: To indicate that something must be done: She has to go to America, on the launch of a new product. I have to mail the letter by today itself. Every person has to follow the traffic rules. How to remember the difference The best way to remember the difference between these two is that you can use must when you think something is necessary to do, but when you are obliged to do something use have to. Further, the word ‘must’ remain the same in all the three tenses, whereas have to becomes ‘had to’ and ‘will have to’, in the past tense and future tense respectively. I hope it helps, Ei.

I have to charge my phone. because its completely of your choice and its not mandatory at all.

The second one sounds more natural.

I would say either is fine. MUST sounds overly dramatic. HAVE TO sounds more natural.

Hello Ei She Zin. This is a great question. You can say either of the sentence as they are common and used all the time. Keep up the awesome work.