https://www.espn.com/nfl/story/_/id/3115...venue-fans

Here's the relevant part for you:

How exactly will this all work, with an odd number of games?
The NFL's 2021 schedule won't be out for several more weeks, but the formula that decides each team's opponents means teams have known for months who they'd be playing if the 2021 schedule had remained at 16 games. Adding the extra game means adding an extra opponent, and the owners voted some months ago on a format that would determine that extra opponent based on division standings from the previous year.

The league will match each division with a division in the other conference, rotating those matchups each season, and the team that finished first in one will play the team that finished first in the other, and so on. The current plan is to match interconference divisions that played each other two years ago, which means that, in this first 17-game season:

AFC East teams will play NFC East teams

NFC North teams will play AFC West teams

NFC South teams would play AFC South teams

NFC West teams will play AFC North teams

So, to determine the specific matchups, look at those pairings and see which teams finished in which spots in the standings in 2020. The Washington Football Team, which finished first in the NFC East, would play its extra game against the Buffalo Bills, who finished first in the AFC East. The Chicago Bears, who finished second in the NFC North, would play the Las Vegas Raiders, who finished second in the AFC West. The Carolina Panthers, who finished third in the AFC South, would play the Houston Texans, who finished third in the AFC South. And so on.

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