The number you'll most often get when you ask this question is, "About 2%." Wait, what? Yes, that is it... for every hundred "followers" you have of your business page about 2 will see any given post, maybe.
You see the algorithms of everyone's favorite social media platform have changed so much in the last couple of years, it has become a pay-to-play platform. Even if you are "Boosting" you're likely missing a key component or two like TARGETING and FREQUENCY.
Gone are the days where a business can get new customers on Facebook for.... FREE. The bottom line is you have to spend money on Facebook to call it successful advertising.
Not many people will see your posts, and even less with each coming year.