Effective hp is another method of evaluating the survivability of a build. To explain this with an example, we can see (using the graph above) that if I were to have 12,000 hp and 100 defense sp, my effective hp would be closer to a value of 34286--over double the original value. Due to how defense reduces damage, we can treat it as a rational function when increasing effective HP. effective hp = hp/(1-% of damage reduced) As the percent approaches a value of 1, the rate at which effective hp rises speeds up. As a result, even though the amount of % less damage taken you get per sp goes down as sp allocated goes up, the overall effect per sp actually increases as the amount allocated goes up. Now that the explanation is finished, here's the multiplier of hp for defense in increments of 10 sp. 0 defense = x1.00 10 defense = x1.10 20 defense = x1.22 30 defense = x1.35 40 defense = x1.50 50 defense = x1.66 60 defense = x1.85 70 defense = x2.05 80 defense = x2.29 90 defense = x2.55 100 defense = x2.86 110 defense = x3.19 120 defense = x3.60 130 defense = x4.05 140 defense = x4.59 150 defense = x5.21 And here's another graph made by @LegionGlory which gives a visual representation of it (in percents). Note: True damage bypasses defense (eye laser), so it's important to keep that in mind.