Ability Haste Calculator

Most players still do the math on ability haste like it is the old cooldown reduction stat, and that math is wrong. 50 ability haste does not mean 50% shorter cooldowns. It means about 33%. The gap between what a haste number looks like and what it actually delivers gets bigger the higher you stack it, and this calculator exists to put a real dial on that gap instead of leaving it as a vague feeling that haste items "feel weaker than they used to."

The Actual Formula

Ability haste converts to a percent cooldown reduction through Percent CDR = 100 × Haste / (Haste + 100). Cooldowns then shrink by dividing, not subtracting a flat percentage: Actual Cooldown = Base Cooldown / (1 + Haste / 100). Both formulas describe the same curve, one in percent terms, one in seconds. At 50 haste you get 33.3% reduction, not 50%. At 100 haste you get 50%, at 200 haste you get 66.7%. The curve keeps climbing forever, unlike the old stat, but every additional block of haste buys a smaller slice of the pie than the block before it.

What the Old CDR Stat Was

Before the 2019 rework, League used a stat that was, confusingly, also often shortened to "CDR," and it worked completely differently: it was a flat percentage, one point of the stat was one percentage point of cooldown reduction, full stop, and it was capped at 40% for almost every champion (a handful of exceptions could push slightly higher through specific runes or masteries at the time). That system had a real design problem: because it was a hard percentage subtracted from cooldowns, the closer you got to the 40% cap, the more valuable each additional point became, since cooldowns approach zero and a build could get uncomfortably close to spamming abilities on near-zero downtime. Riot rebuilt the stat specifically to invert that curve, ability haste makes each additional point worth progressively less, not more, which is why it was allowed to be uncapped.

Why Your First Points Matter Most

The marginal value of ability haste, how much extra percent reduction your very next point buys, is the derivative of the main formula: Marginal Value = 10,000 / (Haste + 100)². At zero haste, that works out to almost exactly 1% per point, which is exactly what the old, naive, linear assumption expects. That is not a coincidence, at low haste values the modern formula and the old flat-percentage mental model nearly agree with each other. The divergence only shows up as haste climbs: by 100 haste, your next point is worth roughly a quarter of a percent, by 200 haste it is down to about a ninth of a percent. This calculator's curve chart plots exactly that dropoff, and the marker on it moves to show where your current build actually sits on the curve, not just what the raw number implies.

Where Ability Haste Actually Comes From

Haste stacks from several different places at once, which is exactly how players end up at 100+ without noticing: base runes like Cosmic Insight and Absolute Focus grant flat haste outright, mythic and legendary items across the AP tree carry it as a core stat rather than a bonus, and several champion passives and ultimates grant haste as a scaling effect that goes up with rank or stacks. None of those sources care what the others are doing, they all add together into one flat number before the mitigation formula ever runs. That additive stacking is part of why the diminishing-returns curve matters so much in practice, a player who casually picks up haste from three or four unrelated sources can clear 100 total without ever buying a single dedicated haste item, and at that point every further source is already deep into the flat part of the curve.

A Worked Example

Say an ability has a 10 second base cooldown and you are running 50 ability haste. The naive guess says 50% off, a 5 second cooldown. The real formula says 33.3% off, 10 / (1 + 50/100) = 6.67 seconds, over a second and a half longer than the naive guess. Push to 100 haste (a realistic number with a haste-focused item build plus runes) and the naive guess claims 100% reduction, an ability that never goes on cooldown, which is obviously impossible. The real formula gives 50% reduction, a 5 second cooldown, exactly half. That gap between an impossible claim and a real, usable number is the whole reason this calculator exists.

How to Use This Calculator

Enter the ability's base cooldown at your current rank (check the ability tooltip in champion select or in-game), then enter your ability haste, either by typing it or dragging the slider. The two dials update immediately, one showing exactly how many seconds your next +10 haste would save right now, one showing your real percent cooldown reduction. The cooldown figure below converts that into an actual number of seconds, and the curve chart shows exactly how much value your next point of haste would add if you bought more.

Frequently Asked Questions