Spellcasters receive bonus spell slots
for high casting abilities. As with most in-game effects of abilities,
these bonuses are determined by the modifier for the relevant ability: intelligence for assassins, beguilers, monster hunters, warmages, and wizards; wisdom for blackguards, clerics, druids, paladins, rangers, and voodan; and charisma for bards, hexblades, and sorcerers. In order to receive a bonus spell slot of a given level, the caster must have spell slots of that level by virtue of class level. For this purpose, having "0" spell slots counts (but having "-" spell slots does not).
As a general rule, the number of bonus spell slots of a given level is (modifier − spell level)/4 + 1, rounded down. There are never bonus spell slots for cantrips (level 0 spells).
| Score | Modifier | Bonus spell slots by spell level | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | ||
| 3 | -4 | Cannot cast spells tied to this ability | ||||||||
| 4-5 | -3 | |||||||||
| 6-7 | -2 | |||||||||
| 8-9 | -1 | |||||||||
| 10-11 | 0 | - | Cannot cast these spell levels | |||||||
| 12-13 | +1 | 1 | - | - | ||||||
| 14-15 | +2 | 1 | 1 | - | - | - | ||||
| 16-17 | +3 | 1 | 1 | 1 | - | - | - | - | ||
| 18-19 | +4 | 1 | 1 | 1 | 1 | - | - | - | - | - |
| 20-21 | +5 | 2 | 1 | 1 | 1 | 1 | - | - | - | - |
| 22-23 | +6 | 2 | 2 | 1 | 1 | 1 | 1 | - | - | - |
| 24-25 | +7 | 2 | 2 | 2 | 1 | 1 | 1 | 1 | - | - |
| 26-27 | +8 | 2 | 2 | 2 | 2 | 1 | 1 | 1 | 1 | - |
| 28-29 | +9 | 3 | 2 | 2 | 2 | 2 | 1 | 1 | 1 | 1 |
| 30-31 | +10 | 3 | 3 | 2 | 2 | 2 | 2 | 1 | 1 | 1 |
| 32-33 | +11 | 3 | 3 | 3 | 2 | 2 | 2 | 2 | 1 | 1 |
| 34-35 | +12 | 3 | 3 | 3 | 3 | 2 | 2 | 2 | 2 | 1 |
| 36-37 | +13 | 4 | 3 | 3 | 3 | 3 | 2 | 2 | 2 | 2 |
| 38-39 | +14 | 4 | 4 | 3 | 3 | 3 | 3 | 2 | 2 | 2 |
| 40-41 | +15 | 4 | 4 | 4 | 3 | 3 | 3 | 3 | 2 | 2 |
| 42-43 | +16 | 4 | 4 | 4 | 4 | 3 | 3 | 3 | 3 | 2 |
| 44-45 | +17 | 5 | 4 | 4 | 4 | 4 | 3 | 3 | 3 | 3 |
| 46-47 | +18 | 5 | 5 | 4 | 4 | 4 | 4 | 3 | 3 | 3 |
| 48-49 | +19 | 5 | 5 | 5 | 4 | 4 | 4 | 4 | 3 | 3 |
| 50-51 | +20 | 5 | 5 | 5 | 5 | 4 | 4 | 4 | 4 | 3 |
| 52 | +21 | 6 | 5 | 5 | 5 | 5 | 4 | 4 | 4 | 4 |