Check out this Gear Enhancement Probability Guide for Dragon Nest by Puru:
Note: You can go down in Levels on Epic Level 5s and Rares can go down at 8
Item to +1
100% Success Chance
Item to +2
100% Success Chance
Item to +3
100% Success Chance
Item to +4
80% Success Chance
Item to +5
60% Success Chance
Item to +6
50% Success Chance
Item to +7
45% Success Chance / 25% Break Chance
Item to +8
40% Success Chance / 25% Break Chance
Item to +9
35% Success Chance / 25% Break Chance
Item to +10
30% Success Chance / 25% Break Chance
Item to +11
25% Success Chance / 25% Break Chance
Item to +12
20% Success Chance / 25% Break Chance
Failing can result in losing 1-2 levels.
Item to +13
15% Success Chance / 25% Break Chance
Failing can result in losing 1-2 levels.
Item to +14
5% Success Chance / 25% Break Chance
Failing can result in losing 1-3 levels.
Item to +15
1% Success Chance / 25% Break Chance
Failing can result in losing 1-3 levels.
+13 turns your blue light in to red?