A unit that is decaying is aged 5 years per combat round and has a variable chance to take damage based on the age of the unit. The number of years added is modified by normal effects that affect age rate, such as quickness, slow, or an unaging bless. Affected units may then take damage, which is calculated as (Old Age penalty * 5 + closed d10 - 1 + number of years actually aged)/10, rounded down. Additionally they are subject to the usual effects of age, which may include gaining afflictions and suffering additional damage if the unit is old.

An affected unit has a 1% chance to make a magic resistance check vs 14 every round of combat to be free of the decay¹⁾.

Like poison and profuse bleeding, decay will continue to apply its effects to units in the 20 turns following completed combat.