How are comments ranked within a thread?

Reddit offers several sorting options for comments within a thread, and the default sorting is "Best," which uses an algorithm designed to surface comments that are both positively received and statistically likely to remain highly rated as more votes come in. Understanding these sorting modes explains why some comments appear at the top even when they are not the most upvoted. The Best algorithm uses a statistical confidence model — specifically a Wilson score interval — to rank comments based on the ratio of upvotes to total votes rather than the raw vote count alone. A comment with 50 upvotes and 0 downvotes scores higher under this model than one with 200 upvotes and 150 downvotes. The algorithm also accounts for the uncertainty created by having few votes: a comment with one upvote and no downvotes is not ranked above a comment with 100 upvotes and 5 downvotes, because the small sample size makes the single-vote comment's rating statistically unreliable. The Top sorting mode ranks by raw score — upvotes minus downvotes — without the statistical adjustment. This means a comment with a high net positive score appears at the top regardless of its upvote ratio. The Controversial sorting surfaces comments that have accumulated large numbers of both upvotes and downvotes, indicating divisive content. New sorting simply shows comments in reverse chronological order, which is useful for following an ongoing conversation or finding recent additions to an old thread. Hot sorting, when available, adds a time-decay element to reward comments that received votes recently rather than just those that accumulated the most votes overall over the post's entire history. This helps newer comments in active discussions gain visibility rather than being permanently buried beneath early top comments. By default, most threads display in Best mode, which is calibrated to give first-time readers the comment most likely to be genuinely useful, correct, or representative of community consensus.