Here's the boosts per Level for 1 IV:
Level 1-99: 0
Level 100: 1
IVs boost stats by itself when a Pokemon is level 100, and here is the formula for levels:
mathfloor[x(y/100)] | Where y is the IV and x is the Pokemon's level.
mathfloor means to round down.
For example, an 8 IV in a stat (y = 8) boosts the stat:
+0 from Levels 1-12
+1 from Levels 13-24
+2 from Levels 25-37
+3 from Levels 38-49
+4 from Levels 50-62
+5 from Levels 63-74
+6 from Levels 75-87
+7 from Levels 88-99
+8 at Level 100
Or, a 31 IV (image).
Source: Experience
