Buying half points: what they cost, and what they are worth

The standard advice on buying half points is that the one off 3 is the most valuable move in football, that books know it, that they charge 25 cents for it, and that you should therefore leave it alone and buy elsewhere.

The first three of those are still true and the conclusion no longer follows. Books have quietly stopped charging 25 cents. Across 5 sportsbooks the half point across 3 now costs an average of 18.3 cents, and it is worth 20 to 24. The 7 — the number those same guides send you to instead — costs 14.1 and is worth 13 to 15. The advice is backwards on both.

How both numbers are measured

These are two separate measurements and the whole point is the comparison, so it is worth being clear about where each comes from.

What it costs is not modeled at all. It reads consecutive rungs on the alternate-spread ladder inside a single book — a book showing −3.5 at −110 and −3 at −128 is charging 18 cents for that half point, and there is nothing to estimate. 7,238 adjacent pairs near the money across 5 books and 100 games, with standard errors of a few tenths of a cent on every entry below.

What it is worth comes from how often games land on the exact number you are stepping over. That is priced in expected value rather than by subtracting one American price from another, which is meaningless across the +100/−100 boundary. Note that a half point can convert a loss into a push, or a push into a win, and those are worth different amounts.

Every half point worth having an opinion about

The chance column is the probability of landing on that exact margin from the side you are betting. About 15% of games end on a margin of exactly 3, and roughly half of those fall on each side — so the number that matters to your ticket is around 8%.

Which direction you are moving matters, and no book prices it. Going from −3.5 to −3 turns a one-point loss into a push and is worth 24 cents. Going from −3 to −2.5 turns that push into a win and is worth 20. Books charge one price for both, so the first is the better buy by four cents on an identical ticket at an identical number.

Everything away from a key number is priced about right. The 4 is worth 7 cents and costs 7.5; the 1 and the 2 are worth 6 and cost 5.4 to 5.8. There is no systematic bargain in ordinary half points, which is what you would expect — nobody needs a model to price a number nothing lands on.

The same half point, opposite verdicts

Pooled across ordinary half points these five books are indistinguishable from each other. The disagreement is concentrated entirely on the numbers that matter, which is exactly where a flat “buy your points at book X” rule would go wrong.

Crossing 7 is worth 13 to 15 cents. At William Hill it costs 10.4 and is a small buy. At BetMGM it costs 16.0 and is a losing one. Same bet, same number, opposite answer — and the gap between those two books is larger than the edge itself.

William Hill charges the flattest curve on key numbers and is cheapest on 3, 7 and 10. It is also the dearest of the five on 1 and 2, which is the trap in reading a single row of this table as a general recommendation.

What to actually do with this

• Buy onto 3 when you can. It is the one half point in football that is reliably worth more than it costs, and the reason it is available is that the price has come down while the advice has not.
• Leave the 7 alone unless your book is cheap on it. At the average price it is a coin flip with extra steps. It becomes a bet only at a book charging under about 13 cents.
• Never buy a half point away from a key number. Those are priced correctly and you are paying the vig for nothing.
• Check your own book before you generalize. The spread between the cheapest and dearest book on 3 is 6.1 cents, which is a third of the price. Whether this is worth doing at all depends on where you play.

One caveat worth stating plainly: these edges are a few cents on a bet, not a strategy. Buying the right half point at the right book is worth having and it will not turn a losing card into a winning one. It belongs in the same category as line shopping — a small structural saving you take every time, rather than an angle you go hunting for.

Why 3 and 7 dominate in the first place is covered in NFL key numbers: why 3 and 7 decide everything. The market built on moving a spread six or seven points at once is the teaser, in NFL teasers: the window most guides get wrong. And for how a price in cents becomes a break-even percentage, see betting odds explained. Book-by-book pricing across the whole board is in the sportsbook rankings.

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