The Kansas City Chiefs are preparing to host a divisional-round matchup at Arrowhead. Andy Reid is drawing up head-spinning goal-line plays, and Patrick Mahomes is taking aim at the conference title game. The territory may feel familiar, but this is also a new frontier.

For the first time in the Mahomes era, the Chiefs aren’t entering this round fresh — they’re coming off a wild-card weekend when they actually had to play their way in. They handled Ben Roethlisberger and the Pittsburgh Steelers, no sweat. Their next game will be decidedly more challenging as Josh Allen and the Buffalo Bills thunder into town after steamrolling the New England Patriots.

The Chiefs land in this predicament because of the NFL’s expanded postseason field and a wild (and wildly frustrating) Week 17 loss to Joe Burrow’s Cincinnati Bengals in Week 17. In blowing two 14-point leads and bungling a late-game situation, Kansas City handed the AFC’s No. 1 seed, and only first-round bye, to the Tennessee Titans.

Some repercussions from that misstep are obvious: The Chiefs had to play last weekend, which despite the lopsided matchup carried risk of a loss or a season-derailing injury to a major contributor. Now, they will face drastically better competition than they would have with the No. 1 seed — the Bills actually rate as a better team than the Chiefs by most advanced metrics, including Football Outsiders’ DVOA. And even with a win, the franchise could face a true playoff road trip for the first time in 12 postseason games, since losing to the Patriots in the divisional round after the 2015 season.

Intuitively, it looks less advantageous. With byes in shorter supply in the new NFL playoff format, though, we wanted to know exactly how much damage the Chiefs did to their chances at a third straight trip to the Super Bowl.

What is that bye worth? And will it cost them?

The value of a bye in the NFL playoffs

Taking a 30,000-foot view, getting that first-round bye can look almost like a prerequisite to winning the Super Bowl. Since divisional realignment in 2002, 76% of Super Bowl participants had a bye, and that trend has been more pronounced in recent years. Last year’s Tampa Bay Buccaneers were the first team to even reach the game after playing on wild-card weekend since 2012.

That doesn’t really answer our question, though. Especially when two teams per league got byes, those numbers essentially tell us that the best teams usually win — not a groundbreaking insight.

To drill down further, I looked at how those top seeds coming off a bye performed only in the divisional round immediately following the open week. Since 2002, they are 52-22 against their less rested challengers — meaning they have played roughly 12-win football (in a 17-game season) against other playoff-level competition. The past decade is even more extreme: Teams coming off byes are 30-8 — about a 13.5-win pace — since 2011.

So, if you’re keeping track at home, all signs point to having a bye being extremely helpful. However, those numbers still don’t account for the fact that better teams are trudging ahead without byes in this new format, or for the reality of difficult matchups. To better understand the predicament the Chiefs face against the Bills, we can use FiveThirtyEight’s win probability metric to isolate Kansas City’s situation.

Their quarterback-adjusted forecast gives the Chiefs a 65% chance at winning on Sunday, while their traditional forecast pegs it at 61%. For perspective, those teams coming off byes since 2002 have won 70.3% of their games, while their average expected win probability headed into the games was 65.9%, making for a difference of 4.3 percentage points.

Creating a sample of games similar to Chiefs-Bills, we can take all the playoff games since 2002 where the host had a win probability between 59% and 66%. The 19 teams with such win probabilities coming off a bye went 14-5, winning at a 73.9% clip (over other playoff-caliber teams!) despite an average win probability of 63.5%. That’s a boost.

The Chiefs, however, didn't have a bye this season. They're simply a home team that played just as recently as their formidable opponents. The 31 home teams to face that situation since 2002, which include conference title game participants, have gone 19-12, winning 61.3% of the games where the average win probability was … 62.4%. These teams basically win as often as FiveThirtyEight’s model would expect.

Football always operates on small sample sizes, so it’s far from a rule, but the data from the NFL’s recent history supports our logical suspicion that a bye week provides a serious lift.

Why the Chiefs’ loss isn’t the Titans’ gain

What that data also hints at is a major difference between home-field advantage and bye-week advantage.

The Titans — a weaker team by any statistical estimation — are beneficiaries of that bye-week boost this week, but it’s a fleeting edge. Even now, they have only slightly better odds of beating the Bengals (-190 at BetMGM) than the Chiefs have of taking down the Bills (-125).

On the other hand, the Chiefs could outrun their disadvantage by beating Buffalo. Losing that bye could cause big trouble for the Chiefs this weekend, but the fallout from their Week 17 stumble basically ends there.

If the Titans and Chiefs were to advance and meet next weekend, the evidence suggests there’s little advantage gained from the game being in Nashville. Numerous studies have documented the decline of home-field advantage in the NFL, even if you disregard the stilted pandemic season in 2020.

Data from NFELO tracking the effects of home fields shows that over in the NFC, the Green Bay Packers may still be working with a significant edge, but few environments make any difference at all. None of the remaining AFC teams boast a notable home-field advantage.

That puts the Titans behind the eight ball if they advance past Cincinnati. They would no longer be coming off a bye, and any way you slice it, they rate as a less efficient team than either the Chiefs or Bills. That’s reflected in their third-place +325 odds of winning the AFC at BetMGM.

Whoever walks out of the Chiefs-Bills matchup victorious will likely be favored to reach Super Bowl LVI. And maybe the conference was always setting up to swing on that clash, but by missing out on a bye week, the Chiefs sowed the seeds of some chaos. That championship-level challenge is coming early.