Completion percentage measures one thing: whether the ball reached a receiver. It says nothing about where that receiver was standing.
A quarterback who throws 42 three-yard screens in a game can post a 78% completion rate. A quarterback who attacks the intermediate and deep levels all day might land at 58%. The box score treats those two performances as if the second QB had a worse day. He didn't — he took on more risk with a higher potential return on every attempt. Completion percentage alone can't tell the difference, which is why you need yards per attempt (Y/A) alongside it.
Why completion percentage is built to flatter check-down quarterbacks
The formula is straightforward: divide completions by attempts, multiply by 100. Run any stat line through our completion percentage calculator to confirm the arithmetic. The problem isn't the math — it's what the math ignores.
Every completion counts equally. A one-yard dump-off behind the line of scrimmage contributes the same to completion percentage as a 35-yard strike over the middle. When an offensive coordinator designs a scheme around quick, short throws — slants, swing routes, flat passes — the quarterback's completion percentage climbs almost mechanically. The receiver catches a quick pass, the defense tackles him for a 4-yard gain, and the quarterback's percentage ticks up. That's not a problem with the quarterback; it's a reflection of the system. But it does mean you can't compare completion percentages across different offensive schemes without context.
This matters most when evaluating quarterbacks across teams. A QB running a west-coast scheme with heavy use of the quick passing game will routinely outperform a vertical or play-action-heavy offense in raw completion percentage, even if the second QB is the better decision-maker on an attempt-by-attempt basis.
Yards per attempt: the corrective lens
Y/A divides total passing yards by total attempts — incompletions included. Per Pro Football Reference's passing glossary, it's one of the oldest efficiency stats in football precisely because it penalizes the incomplete pass while rewarding depth of target. A 5-yard completion and a 5-yard incompletion are not equivalent outcomes, but they both figure into Y/A's denominator. That structure forces accuracy and aggression to both appear in the same number.
Historically, a Y/A above 7.0 has separated above-average passers from the pack among full-season NFL starters, while elite single-season marks tend to cluster above 8.5. Pro Football Reference's career passing leaders show that the passers with the highest career Y/A marks are also, without exception, regarded as all-time greats — not because Y/A caused their success, but because it captures the same underlying quality: gaining significant yardage on each attempt, including the ones that fall incomplete.
For a deeper look at why Y/A outperforms raw passing yards as an evaluation tool, see our guide on why yards per attempt matters more than passing yards for QB evaluation.
The two-stat diagnostic: a worked example
Consider two quarterbacks from the same week:
QB A: 31 completions on 38 attempts, 204 yards
- Completion percentage: 31 ÷ 38 × 100 = 81.6%
- Y/A: 204 ÷ 38 = 5.37
QB B: 22 completions on 36 attempts, 298 yards
- Completion percentage: 22 ÷ 36 × 100 = 61.1%
- Y/A: 298 ÷ 36 = 8.28
The completion percentage gap — 81.6% versus 61.1% — looks decisive at a glance. QB A appears far more accurate. But QB A averaged 5.37 yards per attempt, meaning the offense needed roughly two completions to pick up a first down on standard downs. QB B averaged 8.28 yards per attempt, moving the chains on a single completion most of the time.
QB A's 81.6% rate is a product of a short-pass scheme, not superior accuracy. QB B's 61.1% reflects a deeper average depth of target — some of those incompletions were contested throws 15 yards downfield that would have been completions and first downs if caught. The NFL's official passer rating formula, as published by NFL Football Operations, weights both completion percentage and yards per attempt alongside touchdowns and interceptions precisely because no single component tells the whole story.
What the combination tells you
Three diagnostic combinations cover most situations:
High completion %, low Y/A (below 6.5): The quarterback is operating in a scheme designed around short completions. The offense may be controlling the ball, but it's unlikely to win shootouts or overcome deficits quickly.
Moderate completion % (60–68%), high Y/A (above 7.5): The quarterback is taking on depth of target and converting enough to generate real yardage. Incompletions are the cost of targeting further downfield, not a sign of inaccuracy.
Low completion %, low Y/A: Genuinely problematic. The quarterback is neither completing passes nor gaining meaningful yards on attempts — the worst of both dimensions.
The pairing also catches scheme changes mid-season. If a quarterback's completion percentage jumps five points in October but Y/A drops by a full yard, the offense likely shifted to a more conservative, short-route-heavy approach — possibly in response to injury, personnel loss, or game-script pressure. The completion percentage alone would register as improvement.
Frequently asked questions
What is a good completion percentage in the NFL?
NFL starters have averaged between 62% and 68% league-wide in recent seasons, with top performers regularly exceeding 68–70%. Context matters: a 65% rate in a deep-target-heavy offense is a different achievement than 65% in a quick-screen offense, which is why Y/A belongs in the same conversation.
Can a quarterback have a high completion percentage and still play poorly?
Yes. A quarterback who checks down on every third-and-long converts attempts into short completions that preserve completion percentage while the offense goes three-and-out. A high completion percentage combined with a Y/A below 6.0 is a common signature of this pattern.
Why does yards per attempt include incomplete passes in the denominator?
Because an incompletion is a failed attempt that consumed a down. Excluding incompletions from the denominator would reward quarterbacks for throwing the ball away rather than taking a loss on a poor attempt. Including them in the denominator means Y/A reflects the full cost of each throw, not just the successful ones.
Is completion percentage part of the official NFL passer rating?
Yes. The NFL's official passer rating formula uses four components — completion percentage, yards per attempt, touchdown rate, and interception rate — each capped at a maximum contribution to prevent any single outlier from distorting the composite score. Completion percentage contributes one of four equal-weight components.
How is Y/A different from adjusted yards per attempt?
Adjusted yards per attempt (AY/A) adds a yardage bonus for touchdowns and a yardage penalty for interceptions to the numerator before dividing by attempts. Standard Y/A is purely yardage-based. Both use total attempts — including incompletions — as the denominator. AY/A captures decision quality more completely; Y/A isolates pure passing volume per attempt without touchdown or turnover adjustments.
Informational only, not professional advice.