My dh works in the natural gas industry. His old company gave the yearly bonus at the beginning of the year when they did the yearly employee reviews. The amount of the bonus was based on performance for the year. There were 5 levels employee could be rated at, and the highest 4 were given bonuses on a pro-rated basis.
An example would be that a 1 is the highest level/best employee rating. An employee who rated a 1 would get say a 10% bonus of their gross pay for the prior year. A 2 rating would get 8%; a 3 would get 6%; a 4 would get 4%, and a 5 (the lowest possible would be put on probation and get no bonus and have to improve their performance.
There was also a limit on how many employees could be rated at a 1, 2, 3, 4, or 5. So say if there were 20 employees at a station, there could only be three 1's given, five 2's, five 3's, five 4's, and two 5's.
It wasn't given that a bonus would be received or how much the bonus would be. If you wanted a bonus, you had to really stay on top of the game and perform well.
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The way bonuses worked at my hospital was according to how well the hospital had done financially over the year. The bonus was given at Christmas. It is a not for profit public hospital so if the hospital was in the red then no bonuses were given.

If the hospital was ahead financially then a percentage of that "profit" is given in the form of Christmas bonuses. We didn't get a bonus at all last year because the hospital was in the red.
The year we did get a Christmas bonus, it was based on employment status.
Full time employees got like $75; part time got like $50; and prn got $25. It didn't matter what your position, pay, employee standing, or length of employment was.