How long does it take to acquire a good level of vocabulary?
This depends on many things:
If you want to have a vocabulary like a native British student, estimated to be around 20,000 words*, (Coxhead, 2006:25) it may take a very long time, and in any case this may be an unrealistic goal for most students to achieve. However, the good news is that it may not be necessary. It is only necessary for you to know the words you need to operate effectively in English. There may be whole areas of vocabulary you are never going to need because you do not deal with those subjects. On the other hand, you may have a better knowledge of the vocabulary of your subject area than a native speaker who is not informed about that area. Life is short but vocabulary is long, and acquiring it takes time, even in one’s own language. (Wakely, 2003) This means that you have to be prepared to put time and effort into learning vocabulary, so you must balance how much effort it is worth putting in for the benefits you expect to get. If you consider that you can probably only learn a maximum of seven words per day, even if you study every day of the week, every week of the year, allowing two weeks for a holiday, you will probably only accumulate around 2,500 words per year. Of course, you do not always have to study words in order to learn them (see: How do I learn more words?) so you may in fact learn more - if you are one of those star students who dedicates 50 weeks a year, seven days a week to learning vocabulary!
* Of course, this is only an average figure as knowledge of vocabulary obviously varies widely from person to person and how to estimate a person’s vocabulary is a disputed question. See How Many Words?