That is a tough one to answer, as it would be different for practically everyone depending on their set up, having said that...

For my set up it's fairly easy.

My BionX setup has a pedal pressure sensor that measures my input to the pedaling effort, thus, on...

Level 1; I would get 35% assistance added on top of what I put into the pedaling effort. I use it about 90% or nothing...
Level 2; I would get 75% assistance added on top of what I put into the pedaling effort. I use it about 5%...
Level 3; I would get 150% assistance added on top of what I put into the pedaling effort. I use it about 2%...
Level 4; I would get 300% assistance added on top of what I put into the pedaling effort. I use it about 1%...
Throttle: basically not used...

Up to a MAX assist of 40Nm/29.5Lb-ft of torque...

EDIT; My last 3 years Numbers...

240 rides.
18 days 3 Hrs spent on the bike.
6,672Km total ridden.
75,005 Meters climbed.
262,789 calories burned... Yay... BUT, in actuality, since I used some level of assist... I would have only burned...

Level 1; 194,658 calories, 68,131 calories less.
Level 2; 150,165 calories, 112,624 calories less.
Level 3; 105,115 calories, 157,674 calories less.
Level 4; 65,697 calories, 197,092 calories less....

EDIT 2: Oh, Yea, throttle use... 0 calories, pretend pedaling 1 to... what ever you want to make up. Then there is actual pedaling with throttle... A TOTALY guessed at number for anyone doing that, even "if" you think you are pedaling 50% or more... Are you.? I would suspect, NOT... Sorry...