How GammaLine estimates a prop.

The short version

For every prop, GammaLine estimates the chance that the player goes over (or under) the line. It then puts that estimate next to the FanDuel price, converted into the break-even chance the price implies, and explains what’s driving the number.

The estimate is a starting point for your own research, not a verdict. You make the call.

Reading a prop

Every player page shows four numbers. Here’s an illustrative example for Over 0.5 hits at −150:

Estimated chance

62.0%

Model fair odds

−163

Break-even at −150

60.0%

Estimate vs price

+2.0 pts

• Estimated chance is the model’s probability that the prop hits.
• Model fair odds is that chance written as American odds. A 62% chance is fair at about −163.
• Break-even is how often a bet at the current price must win to break even. At −150 that’s 150 ÷ 250 = 60.0%.
• Estimate vs price is the gap between the two. Here the estimate is 2.0 points above break-even.

Break-even, negative odds: |odds| ÷ (|odds| + 100)
Break-even, positive odds: 100 ÷ (odds + 100)

New to this? Read how to read prop odds and what fair odds mean.

Where the data comes from

• MLB: stats and lineups from the MLB Stats API.
• WNBA: stats and schedules from ESPN.
• NFL: stats, rosters, snap counts, depth charts and play-by-play from nflverse; schedules from ESPN; daily player status from Sleeper.
• Prices: FanDuel’s public odds feed (New York by default). Quotes may differ in your state, so always verify the exact line and price in FanDuel.

GammaLine is independent and isn’t affiliated with FanDuel, any sportsbook or any league.

How each sport works

MLB

Hits and total bases model strikeouts, hits on contact and home runs separately, then combine them across a distribution of expected at-bats. Expected plate appearances come from lineup slot, home or away, and the player’s own at-bat share. Small samples are pulled toward league averages. Runs, RBIs, home runs, H+R+RBI and pitcher strikeouts use the established matchup model. More on MLB props.

WNBA

Everything starts with a minutes projection, then per-minute production for points, rebounds, assists and made threes. Combo props come from the same simulated game, so they stay consistent with each other. More on WNBA props.

NFL

Estimates follow usage: targets, carries and pass attempts, weighted 70% on recent games and 30% on longer history, alongside snap counts, depth charts and daily status. More on NFL props.

How we check the models

Each sport has a Model results page in the app. Here are the headline numbers, with the caveats that come with them.

• MLB: the original study covered 120,420 player appearances in 7,172 games and had lower probability error than a recent-hits baseline in all seven markets. The 2025 calibration check covered 34,664 appearances: the average estimate moved from 63.52% to 62.47% against an actual rate of 62.27%, a modest improvement.
• WNBA: all eight markets had lower probability error than a last-10-games baseline. Those seasons were also used during development, so it isn’t an untouched holdout test.
• NFL: over/under calls were right 59.80% of the time (14,453 of 24,168), but simply taking every under was right 57.05% of the time. High-yardage probabilities are still overconfident.

What GammaLine isn’t

• Not a sportsbook. It never accepts or places bets.
• Not a tip service. There are no “locks” and no guaranteed picks.
• Not financial advice. Only bet what you can afford to lose, where it’s legal for you. Responsible gambling resources.