People commonly use commas around however in midsentence, but a semicolon is almost always necessary, before it or after it.

Punctuation marks are navigational marks that signal to the reader how to grasp your meaning, and a case in point involves however. Whether the word appears at the start of a sentence or in the middle, it usually indicates a contrast. However is part of a thought that is contrary to the previous thought.

Using a semicolon before however

The word however commonly shows up in midsentence, as in these examples:
I will do what I can to help; however, I can’t promise anything.
The deadline is a month away; however, we have plenty to do before then.

In those sentences, however is used to mark a contrast with the preceding thought, and a semicolon before it is appropriate because a stronger mark of separation is needed at that location. When you are wondering what mark to use, ask if however is part of the first thought or the second thought. Here, it belongs with the second half of the sentence. Words that are similar to however, such as therefore, furthermore, or consequently (all called conjunctive adverbs), also require a semicolon before them in instances like the examples above.

Using a semicolon after however

In a less common situation, the semicolon will follow however, as in this example:
She had a great recommendation. It’s too late to adopt it this year, however; let’s consider it next year.

However is part of a thought that is in contrast to the previous sentence

Using a comma after however at the start of the sentence

When the word however begins a sentence, insert a comma after it, except in this rare instance:
However you want to proceed, I will be ready to help.

Using commas on both sides of however

Consider the sequence of sentences below. In the second sentence, however indicates a contrast with the previous thought.
We lost the game last night. We already had a playoff berth, however, so the outcome didn’t matter.

In that sentence, however is a nonessential element, because you could remove it without affecting the meaning of the sentence. Nonessential elements should be set off with commas.

To ensure that you are using the right punctuation mark and positioning it correctly, check a resource guide or ask a knowledgeable colleague. People commonly don’t do that. Instead, they guess at the correct way, or they think of how other people have used punctuation in this situation. Asking someone knowledgeable or checking a reliable guide (a book or an online resource) can help you avoid embarrassment and can ensure that you will know how to address the situation next time.