The Gunning fog index is a useful way of evaluating the complexity of any passage of writing. Using a fairly simple formula (looking at sentence and word length), there are a number of tools available that use this index to give you a rough approximation of how many years of education it would take to understand your writing.

A simple passage might be clear to someone with 5 years of education; a complex passage might be clear only to someone with 20 years of education - that’s 8 years after high school!

Don’t worry too much about the exact number, but do try to keep your writing at a level appropriate for your audience. Too complex, and no one will understand.