What is the difference between CDR and Ability Haste in League of Legends?

CDR (Cooldown Reduction) is a percentage that reduces cooldowns multiplicatively, capped at 40%. Ability Haste replaced CDR in League of Legends Season 11 and has no cap. The conversion formula is: CDR% = Ability Haste / (100 + Ability Haste). For example, 100 Ability Haste equals 50% CDR, and 200 Ability Haste equals ~66.7% CDR.

How do I calculate final cooldown from CDR?

Final Cooldown = Base Cooldown × (1 - CDR%). For example, a 12-second cooldown with 30% CDR becomes 12 × (1 - 0.30) = 8.4 seconds. With Ability Haste, the formula is: Final Cooldown = Base Cooldown / (1 + Ability Haste / 100). At 100 Ability Haste, a 12-second cooldown becomes 12 / 2 = 6 seconds.

Does CDR stack additively or multiplicatively?

In most games, CDR sources stack additively up to a cap. In League of Legends, Ability Haste stacks additively with no cap, then the final value is converted to an effective CDR percentage. In World of Warcraft, CDR from different sources is typically multiplicative, meaning each source reduces the remaining cooldown rather than the base cooldown.

What is the CDR cap in League of Legends?

League of Legends replaced the old 40% CDR cap with the Ability Haste system in Season 11, which has no cap. However, there are diminishing practical returns — going from 0 to 100 Ability Haste halves your cooldowns, but each additional 100 Ability Haste yields less relative benefit. Items, runes, and ultimates each have separate Ability Haste pools in some cases.

How much Ability Haste should I build in League of Legends?

For ability-dependent champions, 100–150 Ability Haste (50–60% effective CDR) is a strong target. Mages and supports benefit most from high Ability Haste, while assassins and bruisers often balance it with damage or tankiness. Beyond 200 Ability Haste the marginal cooldown reduction per point decreases significantly.

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⏱️ Essential Mage Tool

Cooldown Reduction Calculator

Calculate your cooldown reduction, ability haste, and final spell cooldowns. Perfect for League of Legends, Dota 2, WoW, and all MOBA/RPGs. Optimize your ability uptime.

⏱️ Calculate Cooldown Reduction

Select Game

Ability Haste (From items & runes) 0

Ability Cooldown Presets

Base Ability Cooldown (Seconds) 10.0s

Calculate Multiple Abilities

📋 Quick Build Presets

🛡️ Common CDR Items

Cosmic Drive

Ability Haste +30

Black Cleaver

Ability Haste +30

Axiom Arc

Ability Haste +25

Ionian Boots

Ability Haste +15

Your Results

Effective CDR

0.00%

Very Low

Minimal impact

Final Cooldown

10.00s

Reduced by 0.00s

Casts Per Minute

6.0

Maximum ability usage

Buff Uptime (10s duration)

100.0%

5s buff: 50.0%

15s buff: 100.0%

🎯 Next Breakpoints

10% CDR +11 Haste

Need 11 total Haste

20% CDR +25 Haste

Need 25 total Haste

30% CDR +43 Haste

Need 43 total Haste

💡 PRO TIP

Consider adding more CDR items. You're at very low CDR.

Understanding Cooldown Reduction

What is Cooldown Reduction?

Cooldown Reduction (CDR) is a stat that decreases the time between ability casts. It's expressed as a percentage and directly reduces your ability cooldowns, allowing you to cast spells more frequently.

Classic CDR Formula

Final Cooldown = Base Cooldown × (1 - CDR%)

Example: 10s cooldown with 40% CDR = 10 × (1 - 0.40) = 6 seconds

Ability Haste Formula (LoL)

Effective CDR% = Ability Haste / (Ability Haste + 100)

Example: 100 Ability Haste = 100 / (100 + 100) = 50% effective CDR

Why Ability Haste?

Ability Haste scales linearly, meaning each point is equally valuable. This prevents CDR-stacking from being overpowered and makes itemization choices more flexible.

CDR Value by Percentage

10% CDR

10s becomes 9s

Minimal

+11% more casts

20% CDR

10s becomes 8s

Noticeable

+25% more casts

30% CDR

10s becomes 7s

Good

+43% more casts

40% CDR

10s becomes 6s

Excellent

+67% more casts

50% CDR

10s becomes 5s

Very High

+100% more casts

When CDR Matters Most

✓ High Priority For:

→ Mages and spellcasters
→ Support champions
→ Ability-based assassins
→ Tanks needing CC uptime
→ Champions with low base CDs

✗ Low Priority For:

→ ADCs and marksmen
→ Auto-attack carries
→ One-shot burst builds
→ Resource-limited champions
→ Split-push specialists

CDR vs Ability Haste Comparison

Classic CDR (Old System)

• Percentage-based reduction
• Diminishing returns at high values
• 40% was often the sweet spot
• Going from 30% to 40% was very valuable
• Used in most MOBAs and older games

Ability Haste (Modern System)

• Flat stat that converts to CDR
• Linear scaling - no diminishing returns
• Every point equally valuable
• 100 Haste = 50% effective CDR
• Used in League of Legends (S11+)

📊 CONVERSION TABLE

30 Haste

≈ 23% CDR

60 Haste

≈ 38% CDR

100 Haste

= 50% CDR

200 Haste

≈ 67% CDR

CDR Build Strategies

🔮

Burst Mages

Moderate CDR (20-30%) is enough for burst combos. Focus on ability power and penetration first, then add CDR for team fights.

→ Priority: AP > Magic Pen > CDR
→ Target: 25-35% CDR
→ One rotation should secure kills

⚡

Battle Mages

High CDR (40-50%) for sustained DPS. Spam abilities in extended fights. Balance with mana/energy management.

→ Priority: CDR = AP > Survivability
→ Target: 40-50% CDR
→ Need mana regen or large mana pool

🛡️

Tanks

Moderate to high CDR (30-40%) for CC chains and peel. More CC uptime means better frontline control.

→ Priority: Resistances > Health > CDR
→ Target: 30-40% CDR
→ Many tank items provide CDR

💚

Enchanters

Maximum CDR (45-50%) for constant healing and shielding. Your team's survivability scales with your CDR.

→ Priority: CDR > Mana Regen > AP
→ Target: 45-50% CDR
→ Rush CDR items early

Frequently Asked Questions

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