Spell DC is a property of all spells, but usually only comes into play when the spell has a saving throw.
Spell save difficulties are not set by the Dungeon master.
Formula to calculate spell save dc 5E.
The proficiency bonus represents your experience from a role playing viewpoint, and your power curve from a game design viewpoint.
A wisdom modifier or an ability’s modifier is usually the part of the ability that is used for attack rolls, defenses, skill checks and other features of your character.
Suppose you managed a proficiency bonus of 5 and an ability multiplier of 7, calculate your spell save dc.
Therefore, your spell save dc is 20.