Publication:Unearthed Arcana/Scaling the Saving Throw

Scaling the Saving Throw
Another way to tweak the massive damage system is to scale the Fortitude save DC based on the damage taken. For every 10 points of damage dealt by an attack in excess of a character’s massive damage threshold, increase the save DC by 2. This rule functions the same regardless of the threshold you choose to use.

For instance if you use the standard 50-point threshold, a hit that deals 50 to 59 points of damage requires a DC 15 save, 60 to 69 points DC 17, 70 to 79 points DC 19, and so forth. If you use the Constitution-based threshold, a character with Constitution 15 would have to make a DC 15 Fortitude save when taking 15 to 24 points of damage from a single attack, DC 17 when taking 25 to 34, DC 19 when taking 35 to 44, and so forth.