[RickM]

The closest to a convention is what is standard for your particular organization (or sometimes industry). If this isn't documented in your employment contract you rely on luck.

Here's a relatively common formula:

Some orgs will bonus a percentage of an employees salary at the end of the year. The higher up the employee the higher the percentage. For instance, a VP may be eligible to receive 20% of his/her $200K salary if Corp X reaches it's goal of $100 million in revenue.

So, if the corp reaches 100% of their projected revenue the employees are entitled to 100% of there bonus percentage. So, the VP above will receive a bonus of $40K. If Corp X doesn't attain it's goal the amount is reduced accordingly.