Middle Calculator

How to use it

1. 1 Label each bet with the team and line, for example Chiefs -2.5 and Bills +4.5. The lines are only labels here.
2. 2 Enter the stake and odds for each bet.
3. 3 Optionally use the balance button to set Bet B so both miss results cost the same.
4. 4 Read the profit if the middle hits, the result if only one bet wins, and the break-even probability.

What a middle bet is

You back Team A at -2.5 with one sportsbook and Team B at +4.5 with another. If Team A wins by 3 or 4 points, both bets win. That is the middle, the window between the two lines. If the result falls outside it, one bet wins and the other loses.

The same idea works on totals: Over 44.5 at one book and Under 47.5 at another win together if the game total lands on 45, 46 or 47.

What the calculator works out

Profit if the middle hits is the profit on bet A plus the profit on bet B. If only A wins, you get A's profit minus B's stake. If only B wins, you get B's profit minus A's stake. The worst case is the smaller of those two.

Break-even middle probability is the average cost of a miss divided by (the middle profit plus that average cost). "Average cost of a miss" is the mean of the two miss results, so it assumes each miss is equally likely. It is exact when the two miss results are equal, and the balance button sets that up. The calculator does not estimate how likely the middle is, because that depends on the sport, the lines and the teams.

Worked example

You bet $110 on Chiefs -2.5 at -110 and $110 on Bills +4.5 at -110. Each bet wins $100.00 if it wins.

If the middle hits (Chiefs win by 3 or 4), both bets win and you make +$200.00. If only the Chiefs bet wins, you make $100.00 minus the $110 lost on the other bet, which is -$10.00. If only the Bills bet wins, it is also -$10.00.

The break-even probability is $10.00 divided by ($200.00 plus $10.00), which is 4.8%. If you think the game finishes inside the window more often than that, the pair has positive expected value; if not, it does not.

Things to check before you bet

A middle usually costs the vig on both bets, as in the example. Cheaper middles come from line moves between books, and those can vanish before you place the second bet. A push on a whole-number line changes the results above, and that case is not modelled here.

The formula

Frequently asked questions