Betting Terms, Defined

Pricing, and the book's cut

Vig (juice, margin)

The book's cut, built into the price rather than charged as a fee. In a two-way market both sides are priced slightly worse than fair, and the gap is the vig. It is the reason a coin-flip market pays less than even money. → Hold calculator

Hold

What the book actually keeps as a percentage of what it takes in, if the money is balanced across both sides. Related to overround but computed on a different denominator, which is why the two numbers rarely match and get confused constantly. → Hold calculator

Overround

The amount by which the two sides' implied probabilities sum to more than 100%. A market priced at 104% has four points of overround. Not the same number as hold. → Hold calculator

No-vig (fair) odds

The price you get after stripping the vig out of a two-way market — the book's view of the true probability, with its cut removed. This is the number worth comparing against, because a raw posted price is always a fair price plus a charge. → No-vig calculator · No-Vig Odds Explained

Odds formats and probability

Implied probability

The win probability a price corresponds to. Every odds format is the same statement in different clothing; implied probability is the format that lets you compare a price against your own estimate. → Odds converter

American odds

Prices quoted relative to 100: a negative number is the stake required to win 100, a positive number is the profit on a 100 stake. The US default, and the format every price on Blitzen is quoted in. → Odds converter

Decimal odds

Total return per unit staked, stake included — 2.50 returns 2.50 for every 1 risked. The easiest format for multiplying legs together, which is why parlay math uses it. → Odds converter · Parlay calculator

Fractional odds

The UK convention: profit over stake, so 5/2 pays 5 profit per 2 risked. Same information, older notation. → Odds converter

Evaluating a price

Expected value (EV)

The average result of a bet per unit staked if the same situation repeated many times, given a win probability and a price. The critical caveat, and the one the calculator states on the page itself: the output is only as good as the probability you put in. EV computed from a guess is a guess with more decimal places. → EV calculator

Break-even probability

The win rate at which a given price returns exactly zero over time. Useful as a bar rather than a target: it tells you what a price is asking you to believe. → EV calculator

Kelly criterion

A stake-sizing formula, f* = (bp − q) / b, that sizes a bet relative to bankroll and to how far your probability estimate departs from the price. Full Kelly is aggressive and unforgiving of estimation error, which is why fractional — half or quarter — Kelly is the practical form. → Kelly calculator

Variance

The spread of outcomes around the average. It is the reason short-run results say very little about whether a process is any good. It is why a rate is worth very little without the sample size it was computed over.

The market over time

Line movement

The change in a number between when it opens and when it closes. A line is a live opinion that updates as money and information arrive — not a prediction that got revised. → How to Read Line Movement

Steam

Fast, broad movement in one direction across many books at once, usually driven by significant money rather than by news. Distinguished from drift — slow movement — in the guide. → How to Read Line Movement

Closing line

The final price before a market closes. It matters because it is the market's last and best-informed opinion, which makes it the standard reference point for grading a decision after the fact. → What Is Closing Line Value

Closing line value (CLV)

Whether the price you took was better than the closing price, measured in points or in cents. It is a research metric about the quality of a price at the moment it was taken — not a statement that a wager made money. You can take a better price than the close on a moneyline and still not clear the juice. → What Is Closing Line Value

Beat-the-close rate

How often a set of decisions took a better number than the closing price, expressed as a rate. Only meaningful alongside its provenance: the population it covers, the sample size, and whether losses are included. A rate quoted without those is not a finding. → What Is Closing Line Value

Walk-forward grading

Testing a model only on data from after the point it was trained, stepping forward through time the way the season actually arrived — so the model is never scored on information it could not have had. The honest alternative to fitting and reporting on the same history. → What Is Walk-Forward Grading

Structural terms

Key numbers

Margins that occur far more often than their neighbours because of how the sport scores — 3 and 7 in NFL football above all. It is why moving a spread across 3 costs more than moving it across 8, and the frequency is measurable rather than folkloric. → Half-point calculator

Hedge

Taking the opposite side of a position you already hold, to narrow the range of outcomes. The arithmetic answers what stake pays the same either way; whether narrowing that range is worth what it costs is a separate question the calculator shows rather than answers. → Hedge calculator

Correlation (in parlays)

Standard parlay math multiplies leg prices as if the legs were independent. When they are not — same-game legs especially — that math misprices the ticket, and the book's margin compounds leg by leg regardless. → Parlay calculator

What a glossary can't do

Knowing the vocabulary is not the same as having a better number than the market, and none of these definitions tells you what to bet. The market's price has already absorbed every injury report and every dollar of sharp money; the default assumption should be that it is right and you are not. We hold ourselves to the same standard and publish the result: our methodology page states plainly that no model of ours clears the vig against the close yet.

What the vocabulary does buy you is the ability to check someone's work — ours included. Read the market, then check its arithmetic. All eight calculators are free and public, no account needed.

Blitzen is an analytics and research tool, not betting advice or a picks service. Nothing here predicts a financial outcome. Sports betting carries real financial risk — wager only what you can afford to lose, and only where it is legal. Must be 21+. If gambling stops being fun, help is available: call 1-800-GAMBLER.