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What a middle is
A middle pairs a low side and a high side of the same number at different books. On a total, that is Over a at one book and Under b at another, with b above a. On a spread, it is the favourite at −a and the underdog at +b. If the final result lands strictly between a and b, both bets win. If it lands outside, one wins and one loses, and you pay roughly the vig on the pair. On whole-number lines, a result exactly on the line pushes that leg.
Live The Middles screen prices every middle window across your books, on main and alternate lines and player props, using the same fitted fair ladder as the +EV finder, and ranks them by EV.
The math
For equal-payout stakes on a $100 total, the pair's EV is the sum over five outcome regions of probability times profit: below a, exactly a, between a and b, exactly b, and above b.
Equal payout: s_lo × d_lo = s_hi × d_hi, s_lo + s_hi = T
EV = Σ P(region) × profit(region)
Worked example
NFL total: Over 44.5 at −110 at DraftKings, Under 47.5 at −110 at FanDuel. Suppose the fair centre is 46 points. For illustration we use a normal distribution with a standard deviation of 13.5 points:
Stakes $50.00 / $50.00 (equal prices)
P(total ≤ 44) = 45.58%, P(45 to 47) = 8.85%, P(total ≥ 48) = 45.58%
Outside the window: one leg wins $45.45, the other loses $50 → −$4.55
Inside the window: both win → +$90.91
EV = 0.9115 × (−4.55) + 0.0885 × 90.91 ≈ +$3.90 per $100 (+3.90%)
Now shrink the window to Over 45.5 / Under 46.5. The only result where both win is exactly 46, which happens about 2.95% of the time, and the pair's EV drops to −1.73%. The width of the window drives everything.
The normal curve is a simplification. Real football scores cluster on key numbers (3, 7, 10 for margins), which can make a window that spans one much better or worse than the normal suggests. The engine uses the fitted fair ladder where one exists, and our standard deviations for most sports are approximations until we fit them from graded results.
Second example: a spread middle on a key number
An NFL favourite is −2.5 at −110 at one book, and the underdog is +3.5 at −110 at another. Both bets win only if the favourite wins by exactly 3.
Outside the window: −$4.55; on exactly 3: +$90.91 (stakes $50 / $50)
Normal curve centred on 3 with sd 13.5: P(margin = 3) = 2.95% → EV −1.73%
Break-even: P(margin = 3) ≈ 4.76%
If P(margin = 3) were 8%: EV +3.09%; if 10%: EV +5.00%
This middle is worth exactly as much as the true chance of a 3-point margin. Football margins land on 3 far more often than a smooth bell curve suggests, because of how the game is scored. That's why the engine uses a fitted ladder where one exists, and why you shouldn't trust a normal approximation on football spreads that straddle a key number. Know where your probability comes from before you treat a one-point window as +EV.
How to read the screen
Middles shares its layout with Arbitrage. The top bar adds a minimum-EV filter (Any EV, EV ≥ 0%, EV ≥ 1%, EV ≥ 2%).
| Column | What it shows |
|---|---|
| EV % | The expected value of the pair as a share of the total staked. Sortable. |
| EVENT / MARKET | Start time, matchup and league; the market, with what is being measured (for a spread, the home team's margin). |
| BOOKS | The low leg and the high leg, each with its book and net price. |
| BET SIZE | Equal-payout stakes for your Target bet, editable. |
| EV | The pair's EV in dollars on those stakes, and the window size. |
Expand a row for OUTCOMES: each result region (below the low line, exactly on it, between the lines, exactly on the high line, above it) with its chance from the fitted ladder and the profit in that case, plus how often the middle hits and pushes. Clicking a row opens the stake calculator with Middle hits, Push and the EV. When a pair can't lose at all, it also shows up on Arbitrage with a + middle tag.
Evaluate a middle yourself
- Find the two prices. On the Odds Screen, open a game's total or spread and look for books hanging different numbers; the line ladder on props does the same for player stats.
- Size the stakes. Equal-payout stakes are the default: each leg's stake is proportional to the other leg's decimal odds. The hedge calculator sizes a second bet against a first.
- Price the window. Estimate how often the result lands inside it. For game totals and spreads, the fair line and the fair ladder on the Odds Screen give you the market's centre; the window probability depends on how scores are distributed in that sport.
- Compute the EV. Multiply each outcome's probability by its profit and add them up. If the sum is negative, you're paying for a lottery ticket.
Pitfalls
- Most middles lose a little. You pay the vig on both legs most of the time. Only the EV, not the dream of hitting, tells you whether a middle is worth it.
- Stale lines. A wide window often means one book is behind. Confirm both prices.
- Modelled distributions. The probability of landing in a window comes from a fitted or approximate distribution, not from the books' own prices.
- Limits. Books can limit or void, leaving one leg unhedged.
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