Here is a text analyzer where you can input a text sample and it will categorize and color-code the words based on frequency. Here is a paragraph from an article on former president of Egypt, Mohamed Mursi:
Mursi's opponents say these demonstrations are still much smaller than the ones that brought him down. However, the Brotherhood has shown its organizational muscle by keeping its vigil running into a third week and bringing in coachloads of supporters from the provinces during the Ramadan fasting month.
If you don't know a word that's highlighted yellow, on the other hand, then you shouldn't feel so bad since the word is not so common (when is the last time you heard someone use the words opponents, demonstrations, organizational, and supporters at the dinner table with Mom and Dad?).
If you click on the section marked ACAD, it will show words that are associated with academic writing:
PLEASE NOTE: Some students seeing this tool for the first time have the mistaken impression that academic writing consists of 100% academic vocabulary. This is not the case! You still need common words to connect your sentences. In my experience, academic sources usually measure from 15-30% academic vocabulary (depending on the topic).
Play around with this. If you're brave, enter a sample from something you've written and report your results in the comments below: How academic are you?