What is the difference between " from ～to～" and "from ～ through～"?

Question

What is the difference between " from ～to～" and "from ～ through～"? For example, are the following sentences same?

I work from Monday to Friday.

I work from Monday through Friday.

Answer 1

There seems to be some regional variation on this topic, so I will report from my AmE perspective.

In your particular example, either option would be understood to mean the same thing: the speaker works at some point during the course of each weekday (Monday, Tuesday, Wednesday, Thursday, Friday).

“From” would probably be omitted in either case as it is not needed to indicate a day range.

Generally speaking, I was always taught to indicate inclusive ranges with the word “through”. This generally has more application in studying mathematics, but could have an impact such as the following:

1. Read up through chapter 3.
2. Read up to chapter 3.

Receiving instruction #1 with no further clarification, I would read chapters 1, 2, and 3. Instruction #2, on the other hand, presents a quandary. It seems most likely that I’m supposed to read chapters 1 and 2, stopping when I reach the start of chapter 3, and that’s indeed what I would think if I were given no other hint as to the instructor’s wishes.

As you can see there’s a lot of iffiness here, so even among native speakers there is occasionally confusion and/or clarification. A misunderstanding such as the following would not be unheard of:

A: We’ll be on the boat Wednesday to Saturday next week.
B: So you’ll be back on land that Saturday?
A: No, we dock Sunday morning and we’re spending Sunday on the road.

As always, consider your audience and the context. Working those five days is such a common occurrence that neither word is likely to confuse anyone as to what you mean. In other cases, you may wish to add “inclusive” after the range to clarify that the whole of the end-limit you’ve named should be considered part of the deal.

Answer 2

If a friend, a native speaker of English, told me, a native speaker of English, that he worked "from Monday through Friday", I would know he meant that he worked every day of the work-week but not on the weekend, Saturday and Sunday.

If he said that he worked "Monday to Friday" I would at first assume the same, though he might possibly go on to say that he worked part-time and his schedule varied, some weeks Monday, Tuesday, Thursday while in other weeks Monday, Wednesday, Friday -- but again, never on the weekend.

Answer 3

If a British English speaker said "I work Xday to Yday", it would normally be understood to mean that he or she worked on the first day named, and all the days following, up to and including the last day named. "Xday through Yday" is a US English variant, an "Americanism".