Skills fire on their own, on a cooldown. Faster Cast Rate (FCR) shortens every cooldown, spells and attacks alike. All of it adds into one total with diminishing returns, and the most it can do is halve a cooldown, at 200%.
Cooldown by FCR
| Faster Cast Rate | Cooldown | Casts as often | A 3s skill fires every |
|---|---|---|---|
| 0% | 100% | 1.00× | 3.00s |
| 10% | 89% | 1.12× | 2.67s |
| 20% | 81% | 1.23× | 2.44s |
| 37% | 73% | 1.38× | 2.18s |
| 50% | 68% | 1.47× | 2.04s |
| 75% | 62% | 1.62× | 1.86s |
| 100% | 58% | 1.73× | 1.74s |
| 125% | 55% | 1.82× | 1.65s |
| 150% | 53% | 1.89× | 1.59s |
| 200% | 50% | 2.00× | 1.50s |
The game turns FCR into speed with D2's own curve, FCR × 160 ÷ (FCR + 120), then divides the cooldown by 1 plus that. Past 200% nothing more is gained.
Sources
- Gear's +% Faster Cast Rate.
- The shared passive
Faster Cast Rate: skills recharge 32% faster at its max. 
Warmth (Sorceress) and 
Fanaticism (Paladin) shorten recharge; 
Burst of Speed (Assassin) shortens cooldowns by 21%.
Meditation (Paladin) and gear's Regenerate Mana add to FCR, as mana regeneration does in D2. Mana from items, leech and kills speeds up casting.- Energy: a quarter of a percent FCR a point.