"Allow someone to do something" often means to give permission in a formal way. For example, "The tourist visa only allows you to stay in the country for 3 months". Parents may or may not allow their children to do certain things; employers may or may not allow their employees to do certain things; states may or may not allow their citizens to do certain things. If something isn't allowed, it is prohibited. "Let someone do something" is often less formal. It may just mean that you enable someone to do a certain thing. For example, "Let me see your photos" simply means "Show me your photos"; "Let me know your plans" just means "Tell me about your plans". A sentence with "allow" can often be rewritten with "let", but not vice versa. For example, you can say "The teacher allowed the children to use dictionaries in the test" or "The teacher let the children use dictionaries in the test", but you it would be strange to say "Allow me to see your photos" to your friend. Two important grammar differences: You allow someone TO DO something; you let someone DO something. 'Allow' can be used in the passive, but 'let' can't. For example, you can say "They allowed us to leave" or "We were allowed to leave". The same sentence with 'let' can only be in the active voice : "They let us leave" - there is no equivalent passive form.

" Let" is informal. "Allow" is formal and carries the implication of an order/command. If you allow your friend to so something, it implies that you are coming from a higher position and may not sound friendly/polite. Let us do something together. The law allows you compensation.

Let me answer it in this way. <- natural Allow me to answer it in this way. <- natural, but a little more formal (slight difference in construction) . Let me ... Allow me to ... . Let the mouse go. <-- natural Allow the mouse to go. <--not so natural. Why? Sounds super formal . I'll take the rest of the day off if you will allow it. <-- slight differences in usage. (more formal) I'll take the rest of the day off if you will me to. <-- slight differences in usage. (more formal, less natural) I'll take the rest of the day off if you will let me. <-- slight differences in usage. .. Let it be. Allow it to be. <-- not the same, well, ring to it. . Pretty much identical. The room is empty, let's let it out. <-- can't use "allow" here :( . I suspect "allow" sounds more formal, mostly because it is less used. So which comes first, the formality, or the less common, I don't know. . Guy opens door for lady, saying "Allow me". <- formal Guy opens door for lady, saying "Let me". <- not so natural Let me help you with that. Allow me to help you with that.

There isn't a big difference.Only the forming of the sentences I guess. Example: I will allow you to stay on the computer for only 30 minutes. I will let you stay on the computer for only 30 minutes.