| Monster level compared to character level | XP gain |
| 3 levels higher and above | 125% |
| 2 levels higher | 120% |
| 1 level higher | 115% |
| Same level monster | 100% |
| 1 level lower | 90% |
| 2 levels lower | 80% |
| 3 levels lower | 70% |
| 4 levels lower | 60% |
| 5 levels lower | 45% |
| 6 levels lower | 30% (no +XP/kill from gear) |
| 7 levels lower | 15% (no +XP/kill from gear) |
| 8 levels lower | 5% (no +XP/kill from gear) |
| 9 levels lower | 1% (no +XP/kill from gear) |
Also here is an XP image chart by Malloy626:
 |
| XP Chart Click for the Full Size |
A chart that displays each act and difficulty. The yellow portion is what I'm guessing is Blizzard's ideal leveling curve.
Note that at 30% or less, +exp and +%exp no longer functions.
Expanded explanation;
This chart provides you with how much experience your character will receive when killing monsters in certain areas. The "Min", "Mid", and "Max" columns represent lowest, average (rounded), and highest monster levels in the act. So if you are level 50 and kill a level 50 monster, you get 100% of the exp, change your level to 60 when killing the level 50 monster and you get 0% of the exp.
- char level +10 or more of monster level = 0%
- +9 = 1% (+exp effects nullified)
- +8 = 5% (+exp effects nullified)
- +7 = 15% (+exp effects nullified)
- +6 = 30% (+exp effects nullified)
- +5 = 45%
- +4 = 60%
- +3 = 70%
- +2 = 80%
- +1 = 90%
- +0 = 100%
- -1 = 115%
- -2 = 120%
- -3 or less = 125%
