Percentage Rollouts

A percentage rollout rule lets you release a flag to a fraction of your users. Instead of turning a flag on for everyone at once, you can start at 10%, verify your system is healthy, then ramp to 50% and finally 100%.

Creating a rollout rule in GrowthBook

On the Feature detail page, click Add Rule.
Choose Rollout (percentage) as the rule type.
Set the Coverage percentage (e.g. 10).
Set the Hash Attribute — this is the user attribute whose value is hashed to decide bucket assignment (usually id).
Optionally add Targeting Conditions to restrict the rollout to a subset of users.
Click Save Rule.

How bucketing keeps users consistent

GrowthBook hashes the user’s hash attribute value (e.g. their id) with the feature key to produce a number between 0 and 1. If that number is below the coverage percentage, the rule matches. Because the hash is deterministic, the same user always lands in the same bucket — raising the coverage from 10% to 50% only adds new users; it never flips existing users.

Ramping a rollout

A typical ramp schedule: start at 10% for 24 hours, watch your error rates and metrics. If healthy, move to 50% for another 24 hours. Then roll out to 100% and remove the flag.

gb.setAttributes({ id: 'user-123' });
if (gb.isOn('new-dashboard')) {
  // user-123 is consistently in the 10% bucket
}

gb.setAttributes({ id: 'user-123' });
if (gb.isOn('new-dashboard')) {
  // user is deterministically in or out based on id hash
}