I once received a job offer that included a bonus based on "company and individual performance." I wanted to have a bit more specific information about the bonus in order to evaluate the level of compensation being offered. I told the HR person who was working with me that I understand that the bonus is subject to performance and therefore not necessarily the same from year to year but I would like a rough estimate so I could better evaluate the offer. She told me that she couldn't do that. I didn't want to prod too hard but I rephrased my question a couple of times but I was unable to get any information about the bonus besides that it was "generous."
In the end I did accept the offer and the bonus was indeed generous. Once I became an employee, it turned out that the formula used to calculate the bonus was completely transparent. I found it strange that they would hide this information from potential hires. Is it common to withhold this kind of information from candidates after giving an offer? Is there anything I can do differently in the future in order to draw out some more useful information?
To be clear, I completely understand that exact numbers are likely impossible to provide. I'm not particularly interested in learning the exact formula that is used to calculate bonuses. What I really want to know is the approximate order of magnitude of the bonus. Are we talking 5% of salary or 35% of salary?