(the asterisk * is a multiplication symbol)
As soon as the round starts you have 180 possible time points. If you kill everyone between 0.0 and 0.9 second you'll receive all 180 points. At second 1.0 you will only have 178 possible points, and it goes down 2 points per second up to 90 seconds. At 90 seconds you will receive 0 bonus points for time.
Time bonus = 180 - (wave time * 2)
You get 25 bonus points times the wave number you're on.
Wave bonus = 25 * current wave
You get 10 bonus points for each kill during the wave. Since the number of enemies is fixed you will always get the same bonus, unless you're playing with someone else, then you will be competing with them for kills.
Kills bonus = 10 * your kills
You get 20 points for each headshot kill during the wave.
Headshots bonus = 20 * your headshots
You get 3 bonus points for each additional 1% accuracy above 25%, up to a total possible bonus of 225 for 100% accuracy.
Accuracy bonus = 3 * (your accuracy - 25)
You start with a possible 400 bonus points for receiving 0 damage. Each unit of damage you take lowers your damage bonus by 2 points. Once you're at 200 damage for a wave you will receive no damage bonus that wave.
Damage bonus = 400 - (damage taken * 2)
Here's a hypothetical:
You finish wave 8 in 76.7 seconds with 18 kills, 4 headshots, an accuracy of 35%, and having taken 103 points of damage. First the game truncates the time to 76 seconds.
Total wave bonus = (wave8*25) + (180-2*time) + (kills*10) + (headshots*20) + [3*(accuracy-25)] + (400-damage*2)
That makes the bonus in this example 712. But if you killed an AK47 carrying enemy as the last guy of the round the numer 862 would come up on screen right as you kill him, 712 + 150 for that kill. And if you get a bonus with the last kill add the bonus number into the last number to come up onscreen before the Combat Performance chart comes up.
When you play co-op, the wave bonus is doubled (50 * current wave), and the kills bonus is quintupled (kills * 50). Everything else is the same.
As few as 4 kills in rapid succession; decreases as time between kills increases.
4 kills without being hit by any enemy fire; resets if hit.
4 headshots during the same wave; does not reset.
5 knife kills in succession; resets if an enemy is killed with anything other than your knife.
Kill 5 flashed enemies during the same wave; does not reset if other kills are made between flash kills.
Kill 4 enemies with the same blast; can only be achieved with explosives, not with guns.
Here is a video showing an example of each type of bonus: