How initiative works
When a fight starts, everyone rolls a Dexterity check: a d20 plus their Dexterity modifier. The Dungeon Master usually rolls once for each group of identical monsters. Then everyone acts from highest to lowest, and that order holds for the whole fight.
Set your modifier with the stepper above and roll.
Ties
In the 2014 rules the Dungeon Master decides ties between monsters and players, and players who tie decide their own order. Many tables break ties by the higher Dexterity score instead. Two creatures with the same bonus tie 5% of the time.
Going first more often
- The Alert feat adds +5, which is worth a lot more than it sounds: against someone with the same bonus it lifts your chance of going first from 47.5% to 70%.
- Advantage on initiative, like a 7th-level barbarian's Feral Instinct, means rolling two d20s and keeping the higher.