My wc insurance allows 2 unanticipated bonuses throughout the year. The key there is "unanticipated", meaning you don't know exactly what it will be. We hope to be able to provide a summer and xmas bonus--and so far things have worked out nicely. Look at your bottom line. Consider the productivity of the employee, the team, etc. There are ways to measure this, but it is an imprecise measure. Give as much as you can and still hold onto your pants. A bonus is a bonus--don't try to develop some formula for performance based success. It doesn't really exist. Allow only as much precision as the underlying subject matter allows. Be generous
A friend worked for Hartney Greymont which did a bonus based on safety (lack of accidents?) which sounded like a great added benefit. Lucas Tree also does preformance based but I don't know specifics. Personally I'd like to see more profit sharing as a preformance based bonus. If the crew is kicking but on a job and makes the boss more money than expected, throw them a bit more. Even an extra $20 at the end of the day makes employees give more of a damn the next day. A previous boss did profit sharing after 2 years of employment split evenly, he'd take about 12k and subtract any unforeseen expense if one occurred then pay out the balance at the end of each year. I don't think that qualifies as you can have a deadbeat getting the same as a star, but it's even handed.