An index that tracks every US stock outside the S&P 500 more than doubled the gains of the benchmark in 2020

• The S&P Completion Index tracks every US stock that's not included in the S&P 500>$4. It its up nearly 33% in 2020, more than double the benchmark's 14% gain.
• The completion index is typically associated with small and mid-cap stocks, but until this week, it counted one very high profile company among its top constituents: Tesla.
• Tesla's 665% gain in 2020 likely drove the completion index's ride upwards, according to a report in The Wall Street Journal>$4.
• Visit Business Insider's homepage for more stories>$4.

A stock index that tracks all US stocks except those in the $4has returned more than double what the benchmark index earned this year.

The index, called the $4, is up nearly 33% this year, compared to a 14% gain for the S&P 500 during the same time period.

The completion index is typically associated with small and mid cap stocks that don't make it into the S&P 500. But one very high profile company was, until recently, counted among the constituents of the S&P Completion Index: $4.

Read more:$4

Before the electric vehicle maker $4, it was the darling of the completion index. Its 665% gain in 2020 likely drove the index's gains, according to a report in $4.

The S&P Completion Index is up 2% since the beginning of this week. Meanwhile, the S&P 500 has stayed relatively flat in that same time period.

The completion index is also home to other 2020 star performers, including Zoom (up over 460% YTD), Square (up 272% YTD), and Moderna (up over 560% YTD). In total the index tracks 3,231 constituents, according to $4.