When to post on Reddit?

This website provides statistics on the average activity in a subreddit throughout the week.
Based on that, it analyzes when the best time is to create a new post, to get the greatest reach possible.

To start, just search for a subreddit and check out its statistics.

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To maximize views for usual posts,
the best time to publish it is Thursday evening,
when, on average, 50 new posts come in,
and 6000 people are online.
To maximize views for exceptional posts,
the best time to publish it is Sunday morning,
when, on average, 100 new posts come in,
and 13000 people are online.

Methodology

The method to determine the optimal post times is quite simple.
It compares the amount of new posts coming in with the amount of online users, so on average, as many users as possible will see your post.

It is different though if you have amazing content to share, and a great headline. Then you'd want to post it during peak traffic times, when most users are online, not when the ratio is best, because that post will quickly rise to the top, and then seen by as many users as possible.