# How to track long-term metrics after stopping enrollment - Docs

Some experiments need more time for metrics to mature than you want to keep enrolling new users.

For example, you're testing two price points and want to measure 90-day revenue and long-term retention. You've reached a good sample size after two weeks, but the metrics won't be meaningful for months. Keeping the experiment running means every new user continues to get randomly assigned to a variant — including potentially worse ones — just so you can keep measuring.

You can avoid this by freezing your participant groups at a point in time. The experiment keeps running and counting conversions for existing users, but no new users are added to the measurement. This lets you roll out the winning variant immediately while your long-term metrics continue to mature in the background.

## Step 1: Note the cutoff timestamp

Decide when you want to stop counting new enrollments. This is typically "now" — the moment you're happy with your sample size and want to lock it in.

## Step 2: Edit exposure criteria

1.  Go to your experiment and click **Edit exposure criteria**
2.  If you're using the default `$feature_flag_called` event, switch to **Custom event** and select `$feature_flag_called`
3.  Add a property filter with type **HogQL** and the expression:

PostHog AI

```
timestamp < '2026-03-23 15:44:00'
```

Replace the timestamp with your cutoff date.

This tells PostHog to only count exposures before the cutoff. Users exposed after this point won't be included in the experiment, even though the experiment is still running.

## Step 3: Roll out the winning variant

With the exposure filter in place, you can safely change your feature flag to roll out the winning variant to all users. New users will get the variant, but they won't appear in the experiment results because their exposures are after the cutoff.

Your existing participant groups stay frozen, and their metrics continue to mature over time.

### Community questions

Ask a question

### Was this page useful?

HelpfulCould be better