Combat only: 50%
Effects that only work in combat or under a condition are counted as active half the time. The same rule applies to every rune and spell.
At most once per 8s
Effects that re-trigger on attacks are counted at most once every 8 seconds, since a single fight only allows so many procs.
Damage valued like healing
Damage to an enemy is valued like healing yourself the same amount, priced with the health regen rate.
Survival factor
Moving faster by some % is counted as that % more effective health, since speed lets you dodge and escape. Value = median max health × the speed gain × the health price.
Move speed % as flat
Move speed % is converted to flat move speed against the median base speed of 350, then priced at the flat rate.
Champion median
Values that depend on the champion, such as health, use the median of all champions at level 1 and level 15.
Skill ranks from level
A champion's ability values depend on rank, so rank is derived from level. The ultimate ranks up at levels 5 / 9 / 13. Remaining points go to abilities 1 → 2 → 3 in turn (1 / 0 / 0 at level 1, 4 / 4 / 4 at level 15). Which ability to max first is a judgement call, so every champion uses the same order. Abilities with a different number of ranks (such as Jayce's 5) follow the same rule, raising the lowest-ranked ability one point at a time; an ability learned from level 1 starts at rank 1.
Conditional bonus: 50%
Bonuses that depend on the target's or your own state (extra effects on burning enemies, detonating marks, "if already ..." bonuses) and effects tied to a position or situation (near turrets, in brush, moving toward a low-health ally) assume the condition holds 50% of the time, so they count at half. Effects triggered by your own death are assumed once per 90 seconds, like takedowns. Empowerments spent by another ability (such as Karma's Mantra) count the bonus once per that ability's cooldown.
One takedown per 90s
One kill or assist every 90 seconds (10 in a 15-minute match) is assumed. Uncapped stacks count half of that as the mid-match average.
Six risky moments
Summoner spells are saved for risky moments, so at most 6 uses in a 15-minute match are counted.
One death = 300G
Avoiding a death saves the 300 gold base kill bounty (official patch notes 4.2). Half the match total is counted as the mid-match average.
One fight per 90s
A 15-minute match is assumed to have 10 fights. Shields and damage blocks that work once per fight are counted as extra health in every fight.
Fight length: 10 s
Crowd control that stops the enemy (stun, charm, etc.) is treated as time you aren't being hit. A fight is assumed to last 10 s, so it counts as holding seconds ÷ 10 × median max health in extra health each fight. Uses are capped like shields: the fewer of cooldown uses and fights.
Read as a similar price
Effects without a price are read as the closest existing formula: vision as avoiding a gank death (half an escape tool's chance), blocking attacks or projectiles as a shield for the same time, untargetable time (invisibility, etc.) as crowd control on the enemy, range as the move speed of the approach distance saved, experience as gold (1 = 0.5 gold), and stolen or reduced enemy stats as stats (or defense) you gain.
Continuous values at midpoint
Values that vary continuously with the target's or your own state (damage rising with the target's missing health or with charge time, attack speed rising with your missing health, etc.) are taken at the midpoint of min and max, the same idea as assuming 50% missing health.
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