Dash: use your modified Speed

SRD 5.2.1 · Actions

At the table

1. Determine the relevant Speed after modifiers.
2. Gain that much extra movement for the turn; choose the relevant special speed when using one.
3. Pay normal movement costs while moving. Dash itself does not remove Difficult Terrain or other costs.

Example decision

A character normally has Speed 30, but an effect reduces it to 15. They take Dash with no other movement changes. How far can they move on the turn across ordinary ground?

Up to 30 feet: 15 normal plus 15 from Dash.

Dash adds the currently modified Speed, not the character’s unmodified number. The result is 30 feet of available movement in this example. Terrain or another restriction can still increase the cost of each foot actually traveled. Taking Dash also uses an action unless a feature explicitly lets the character take it another way.

Watch for this mistake

Dash is not automatically a Bonus Action, nor does it automatically protect against Opportunity Attacks. A class feature may change its action cost; Disengage addresses a different concern.

Ask the table

What is the modified Speed, and which movement costs still apply along the route?

Source rule

When you take the Dash action, you gain extra movement for the current turn. The increase equals your Speed after applying any modifiers. With a Speed of 30 feet, for example, you can move up to 60 feet on your turn if you Dash. If your Speed of 30 feet is reduced to 15 feet, you can move up to 30 feet this turn if you Dash. If you have a special speed, such as a Fly Speed or Swim Speed, you can use that speed instead of your Speed when you take this action. You choose which speed to use each time you take it. See also “Speed.”

Source: SRD 5.2.1, 180. Online guide.