You slow the flow of time around a creature within range that you can see. The creature must make a successful Wisdom saving throw, or its walking speed is halved (round up to the nearest 5-foot increment). The creature can repeat the saving throw at the end of each of its turns, ending the effect on a success. Until the spell ends, on a failed save the target’s speed is halved again at the start of each of your turns. For example, if a creature with a speed of 30 feet fails its initial saving throw, its speed drops to 15 feet. At the start of your next turn, the creature’s speed drops to 10 feet on a failed save, then to 5 feet on the following round on another failed save. Decelerate can’t reduce a creature’s speed to less than 5 feet.