Okay. So from level 1 to 20, for those that aren't sure.
Lvl | Spells a Bard -Knows- | The amount they can cast
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1 | 4, -, -, -, -, -, - | 2, -, -, -, -, -, -
2 | 5, 2, -, -, -, -, - | 3, 0, -, -, -, -, -
3 | 5, 3, -, -, -, -, - | 3, 1, -, -, -, -, -
4 | 5, 3, 2, -, -, -, - | 3, 2, 0, -, -, -, -
5 | 5, 4, 3, -, -, -, - | 3, 3, 1, -, -, -, -
6 | 5, 4, 3, -, -, -, - | 3, 3, 2, -, -, -, -
7 | 5, 4, 4, 2, -, -, - | 3, 3, 2, 0, -, -, -
8 | 5, 4, 4, 3, -, -, - | 3, 3, 3, 1, -, -, -
9 | 5, 4, 4, 3, -, -, - | 3, 3, 3, 2, -, -, -
10 | 5, 4, 4, 4, 2, -, - | 3, 3, 3, 2, 0, -, -
11 | 5, 4, 4, 4, 3, -, - | 3, 3, 3, 3, 1, -, -
12 | 5, 4, 4, 4, 3, -, - | 3, 3, 3, 3, 2, -, -
13 | 5, 4, 4, 4, 4, 2, - | 3, 3, 3, 3, 2, 0, -
14 | 5, 4, 4, 4, 4, 3, - | 4, 3, 3, 3, 3, 1, -
15 | 5, 4, 4, 4, 4, 3, - | 4, 4, 3, 3, 3, 2, -
16 | 5, 4, 4, 4, 4, 4, 2 | 4, 4, 4, 3, 3, 2, 0
17 | 5, 5, 5, 4, 4, 4, 3 | 4, 4, 4, 4, 3, 3, 1
18 | 5, 5, 5, 5, 4, 4, 3 | 4, 4, 4, 4, 4, 3, 2
19 | 5, 5, 5, 5, 5, 4, 4 | 4, 4, 4, 4, 4, 4, 3
20 | 5, 5, 5, 5, 5, 5, 4 | 4, 4, 4, 4, 4, 4, 4
And for what Charisma does to the amount of spells you can cast a day..
Score | Bonus per day by spellslot
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10-11 | 0, -, -, -, -, -, -, -, -, -
12-13 | 0, 1, -, -, -, -, -, -, -, -
14-15 | 0, 1, 1, -, -, -, -, -, -, -
16-17 | 0, 1, 1, 1, -, -, -, -, -, -
18-19 | 0, 1, 1, 1, 1, -, -, -, -, -
20-21 | 0, 2, 1, 1, 1, 1, -, -, -, -
22-23 | 0, 2, 2, 1, 1, 1, 1, -, -, -
24-25 | 0, 2, 2, 2, 1, 1, 1, 1, -, -
Of course this table continues but since I've not seen any attribute gear on the server yet, I don't see much reason to do so.
Hopefully this helps.