The following formulas are important to epic spellcasters.
Epic Spells Per Day: Knowledge (arcana), Knowledge (religion), or Knowledge (nature) ranks ÷ 10 (round down).
To Cast an Epic Spell: Spellcraft check (DC = epic spell’s Spellcraft DC).
Level of an Epic Spell: Epic spells are considered 10th level for the purpose of Concentration checks, spell resistance, and other determinations.
Saving Throw for an Epic Spell: DC = 20 + key ability modifier.