May and might are both common modal verbs. Here are a few important rules for modal verbs:

• Modal verbs do not take any endings like -s, -ed or -ing
• Modal verbs are followed by the base form of another verb (may do, might be)
• Modal verbs make questions by inverting the subject and the modal verb (may I)

POSSIBLITY
Both may and might can be used to express possibility. Some examples:

• It might rain tonight.
• She might not come to the meeting.
• I may need your help on this project.
• He may be waiting for us.

Negatives:

• The negative form of may is may not + base form. We never use a contraction for this negative. (You might find the word mayn’t in a dictionary, but it is not used.)
• The negative form of might is might not + base form. The contracted form (mightn’t) is not used in American English, but it is used in British English.

Questions:

• When may is used in a question, it refers to permission. See the explanation of permission below.
• Might can be used in a question about possibility.
• Might it rain later? (This form is not used in American English.)
• Do you think it might rain?

May and might in the past:
The past form is may/might + have + past participle.

• I might have left my phone at home.
• She might not have seen my email.
• Where is Amanda? I think she may have forgotten about the meeting.

Do not confuse may be and maybe. Maybe is an adverb meaning ‘possibly’. It is usually used in the beginning of a sentence.

• Maybe I will take a vacation next month.
• Maybe it will rain. / It might rain.

PERMISSION
May can be used to express permission. This could be in the context of an adult speaking to a child or an authority speaking in a formal context.

• You may have a cookie after you finish your dinner. (adult to child)
• You may now begin your exam. (professor to students)

Questions:
May can be used in a question to ask permission. The subject is usually first person singular or plural (I or we). May is considered more polite than can.

• May I borrow your pen?
• May I use your restroom, please?
• May we come in?

In British English, might can also be used to ask permission.

• Might I borrow your pen?

Note that we don’t use may to ask another person to take an action, so you cannot say “may you”. If you want to make such a request, you can ask “can you”, “could you” or “would you”.

• Could you please turn down the music? I’m trying to study. (NOT: May you please…)
• Would you help me clean the house? (NOT: May you help me…)

Students often ask:
When may and might are used for possibilities, is there any difference between them? Like may is a 50% possibility and might is a 70% possibility? Answer: No, there is no difference like this. They are equal in terms of possibility.