Health calculator
Health starts at 5, traits add or take away, and from 25 age wears it down a little each year. Pick an age and traits to see the expected health and when death checks begin.
Traits that change health
How the game counts it
From age 25, once a year the game rolls a chance of 0.075 + 0.022 × (age − 25) to lower health by 0.125 (NOldAge: LOWER_HEALTH_*). The calculator adds up those chances: the expected loss, not one character's luck. Traits add their health modifier, elderly_health from 50 and child_health before 16.
Below 3 health the game checks each month whether the character dies, with a 25% monthly chance at 0 health (DIE_HEALTH_TRESHOLD, DIE_HEALTH_CHANCE_ZERO). The defines call the curve between them “quadratic”; the monthly chance shown is 0.25 × ((3 − health) ÷ 3)², our reading of that comment.
Not included: illnesses, wounds, stress breaks, events, lifestyle perks, buildings and court physicians, which change health during play. Sources: common/defines/00_defines.txt (NCharacter, NOldAge); common/traits/00_traits.txt (health, elderly_health, child_health) — patch 1.20.0.3.