What does an NFL win probability calculator do?

An NFL win probability calculator estimates the chance that a team wins from the current game state. This one takes three inputs (the score margin, the minutes left, and which team has the ball) and runs them through a logistic curve, so the same lead is worth more as the clock runs down. It is a simplified illustrative model with hand-set coefficients, not a model fitted to play-by-play data.

The Win Probability Calculator

Margin is from the team's point of view: +3 means leading by 3, −3 trailing by 3. The same model runs the win-probability card on the tools page.

What It Computes

The formula is a logistic curve:

WP = 1 / (1 + e^{−m / s})

m is the score margin plus 1.5 points if the team has the ball, or minus 1.5 if the opponent has it. The model credits possession with 1.5 points.
s = 1.15 × (minutes left + 1)^0.55 stands for how much scoring is still to come. It shrinks as the clock runs, so a fixed margin moves the probability further late in the game.
Minutes are kept between 1 and 60, and the result between 0.5% and 99.5%.

The inputs are the score margin (−50 to 50), the minutes left in regulation (0–60) and possession. There is no field-position input.

Worked Example: Up 3 With 5 Minutes Left

A team leads by 3 with 5 minutes left and has the ball. The calculator returns 81.2%:

m = 3 + 1.5 = 4.5
s = 1.15 × (5 + 1)^0.55 = 3.08
WP = 1 / (1 + e^{−4.5 / 3.08}) = 1 / (1 + e^−1.46) = 81.2%

Give the ball to the opponent instead and m falls to 3 − 1.5 = 1.5, so the same lead is worth 61.9%. Possession alone moves this game by 19.3 percentage points.

The grid below shows how the clock changes a margin, for the team that has the ball:

Margin (with the ball)	30 min left	15 min left	5 min left	2 min left
Down 7	32.7%	26.1%	14.4%	6.8%
Down 3	45.1%	43.0%	38.1%	32.9%
Tied	54.9%	57.0%	61.9%	67.1%
Up 3	64.4%	70.1%	81.2%	89.5%
Up 7	75.4%	83.3%	94.0%	98.3%

Two patterns stand out. A tie is worth more to the team with the ball as time runs out (54.9% at halftime, 67.1% with 2 minutes left), because there is less time for the opponent to answer. And a 7-point deficit with 2 minutes left leaves 6.8% even with the ball.

Every value in this section is the output of the calculator above, run with these inputs.

Limits

The coefficients are hand-set, not fitted. They reproduce the shape of published win-probability curves; the site's game-level dataset cannot fit a real in-game model, so none is claimed.
No field position, down or distance. A team down 3 at the opponent's 20 and one down 3 at its own 20 get the same number.
No timeouts, no team strength. Two evenly matched teams and a mismatch read the same, and the clock is treated as continuous.
The last minute is flattened. Anything under a minute counts as one minute, and overtime is not modelled.

Go deeper

Plain-English guides to the metrics, and the full code-first tutorial.

Explainers Tutorials

NFL Win Probability Calculator: Score, Time Left and Possession