How to Read a Win Probability Factor Breakdown
Team strength, home advantage, rest, injuries and weather—what each factor means and why it moves the number
Start with Team Strength
Every matchup begins with how good the teams are. We use an Elo-style rating to capture relative strength that carries between seasons without overreacting to single results. Details and sources are on our methodology page.
The Factors, One at a Time
- Home and road form. Teams play differently at home vs away. In some sports the home advantage is small; in others it is meaningful. See home field in the NFL.
- Rest and back-to-backs. Daily-schedule sports (NBA, NHL) punish teams playing the second night in a row. See NBA back-to-backs.
- Injuries, weighted by position. A star being out matters more than a depth player. The position changes how big the effect is.
- Weather (outdoor venues only). Cold and wind affect outdoor NFL and MLB games. See NFL weather and MLB weather.
How the Factors Combine
Each factor scores positive or negative for the home team. We weight those scores, add a small built-in home advantage, and pass the total through a logistic curve to get a probability between 5% and 95%. The aim is calibration: teams we call 70% should win about 70% over time. Our live record is 55.8% over 2,927 games, Feb–Oct across all sports; see accuracy.
Reading a Factor Card
On a game page you will see each factor listed as favors, neutral or against the home team, along with its size. If a percentage moved, check which card changed since the last refresh: late injury news or a weather shift is usually the reason.
Pregame vs In-Game Models
Our numbers are pregame only. In-game win probability adds time, score and possession; it answers a different question than a pregame forecast. The two are not directly comparable.
Next Reads
Related Topics
How to Read a Win Probability
What 65% actually means — and how to spot an honest model
NFL Win Probability
How we calculate NFL game outcome probabilities
NBA Win Probability
How we calculate NBA game predictions
MLB Win Probability
How we calculate MLB game predictions
NHL Win Probability
How we calculate NHL game predictions
Frequently Asked Questions
Most changes come from an injury update, a lineup confirmation, or a weather forecast shift at open-air venues. Check the factor cards—one will usually show the move.
No. Each sport has its own weights and some factors don't apply (e.g., weather for domes, back-to-backs for weekly schedules). See Methodology for details.