# Expected value betting: how to find +EV odds > What expected value means in betting, how to remove the vig to find fair odds, how TheRundown's Value Tool flags +EV prices, and Kelly sizing. Published 2026-10-05. Updated 2026-10-05. Canonical: https://therundown.io/blog/expected-value-betting Expected value (EV) betting means placing bets where the price you are getting is better than the outcome's true probability of happening, so that over many such bets, the math favors you even though any single bet can still lose. The key skill is estimating that true probability — which requires stripping the sportsbook's built-in margin out of its price — and then comparing a book's actual price against it. This post covers the EV formula, how to remove the vig to get a fair price, how TheRundown's Value Tool automates that comparison, and the variance and risks that come with the approach. ## What expected value means EV is the average amount you would win or lose per unit staked if a bet could be repeated many times at the same price, against its true probability of winning. Per unit staked: ``` EV = p × (decimal − 1) − (1 − p) ``` where `p` is the true (fair) probability of the outcome, expressed as a decimal, and `decimal` is the price you are being offered. When EV is positive, the price is better than the outcome deserves given its true probability — a "+EV" bet. When EV is negative, you are laying more than the outcome is worth. The hard part is never the formula. It is getting a trustworthy value for `p`. ## Removing the vig to find fair odds A sportsbook's price already has its margin built in. If you convert both sides of a two-way market to implied probability (`1 / decimal` for each), they will sum to more than 100% — that excess is the vig, also called the overround. To estimate the _true_ probability of either side, you rescale the implied probabilities so they sum to exactly 100%. The simplest way to do that is proportional removal: divide each side's implied probability by the sum of both. **Example: a hypothetical two-way market** Say Team A is priced at **−130** and Team B, the only other outcome, at **+110**. **Step 1 — decimal odds** - Team A: `1 + 100/130 = 1.7692` - Team B: `1 + 110/100 = 2.1000` **Step 2 — implied probability** - Team A: `1 / 1.7692 = 0.5652` → 56.52% - Team B: `1 / 2.1000 = 0.4762` → 47.62% **Step 3 — the overround** ``` 0.5652 + 0.4762 = 1.0414 → 4.14% overround ``` **Step 4 — remove it proportionally** ``` no-vig_A = 0.5652 / 1.0414 = 0.5427 → 54.27% no-vig_B = 0.4762 / 1.0414 = 0.4573 → 45.73% ``` Check: 54.27% + 45.73% = 100.00%. Those two numbers are an estimate of each side's true probability, with the book's margin removed. This proportional method is the simplest way to understand what "removing the vig" means, but it is not how TheRundown's Value Tool does it. The Value Tool uses a margin-weighted method on each qualifying book's price, then averages the resulting no-vig price across several qualifying books rather than relying on a single book's margin removal. More books agreeing on a price is a stronger signal than one book's price alone. ## How TheRundown's Value Tool works The Value Tool is a Pro feature: turn it on under Settings → Value Tools, and it shows in game details. It builds its true-price estimate like this: 1. **Qualifying books only.** A sportsbook qualifies for a given market only if it prices every outcome of that 2- or 3-way market. Prediction markets, exchanges, same-family duplicate books, and any book you have excluded in settings are left out. 2. **Remove the margin, then average.** Each qualifying book's price has its margin removed, and the resulting no-vig prices are averaged across those books to produce a single true price per outcome. 3. **Flag the beatable price.** Any book whose actual decimal price beats that average true price is flagged with a green +EV box in game details. 4. **Show the detail on hover.** Hovering the green box shows the expected value, the true (average no-vig) odds, and a recommended stake sized as a percentage of a bankroll figure you type in. Player-prop-style markets with more than three outcomes do not get a value badge, since the qualifying-book and no-vig math is defined for 2- and 3-way markets. Value and +EV calculations are also available as an API feature on the Pro plan and up. ## Kelly sizing, and why the stake shown is "full Kelly" The stake the Value Tool recommends is sized with the Kelly criterion, which answers "what fraction of my bankroll maximizes long-run growth" for a bet with a known edge: ``` f* = (b × p − q) / b ``` where `b = decimal − 1`, `p` is the true probability, and `q = 1 − p`. That is what the tooltip means by a "full Kelly" recommended stake. As general betting-strategy knowledge, not a TheRundown-specific claim: full Kelly is the growth-optimal stake in theory, but it assumes your probability estimate is exactly right, and it produces large bankroll swings along the way. Because no probability estimate is ever perfectly precise, many bettors stake a _fraction_ of Kelly — commonly half — to cut variance substantially while giving up only a portion of the theoretical long-run growth rate. That tradeoff is a personal risk choice, not a fixed rule. ## Variance and the real risks Positive expected value describes an average across many bets, not a promise about any one of them. Keep a few things in mind: - **Any single +EV bet can still lose.** EV only pays off in expectation over a large number of similar bets, and variance in the short run can be large. - **The true-price estimate is only as good as its inputs.** If the qualifying books themselves are mispricing a market, or there are too few qualifying books for a given outcome, the average no-vig price will be off, and a flagged +EV price may not actually be +EV. - **Markets move.** A price that looks +EV when you see it can move before you bet it. - **No outcome is guaranteed.** Nothing here promises profit. Treat EV and Kelly sizing as a disciplined way to decide which bets are worth making and how much to risk, not a guarantee of winning. ## Tools to use - [Expected value calculator](/betting-calculators/expected-value-calculator) — compute EV for a price against a true probability you supply. - [No-vig calculator](/betting-calculators/no-vig-calculator) — remove the vig from a market's prices to estimate true probabilities. - [Kelly criterion calculator](/betting-calculators/kelly-criterion-calculator) — size a stake, full or fractional, from your edge and bankroll. - Odds boards such as the [NFL odds](/odds/nfl) and [NBA odds](/odds/nba): open a game to see the Value Tool's green +EV boxes in game details. 21+. If you or someone you know has a gambling problem, call 1-800-GAMBLER. ## Questions ### What does expected value mean in betting? Expected value (EV) is the average result you would expect per unit staked if you could place the same bet many times at the same price against the same true probability. A positive EV means the price is better than the true odds of the outcome. ### How do you find the true, or fair, probability of an outcome? Start from a sportsbook's price, convert it to an implied probability, then remove the book's margin (vig) so the probabilities for all outcomes sum to 100% instead of over 100%. Try it with TheRundown's [no-vig calculator](/betting-calculators/no-vig-calculator). ### How does TheRundown's Value Tool find +EV prices? For each qualifying book that prices every outcome of a 2- or 3-way market, it removes that book's margin, then averages the no-vig true odds across those books. Any book beating that average true price is flagged with a green +EV box. ### What does the Value Tool's tooltip show? Hovering a green +EV box shows the expected value, the true (no-vig average) odds, and a recommended stake as a percentage of a bankroll you enter, sized using the full Kelly criterion. ### Should I bet the full Kelly stake the Value Tool recommends? Many bettors stake a fraction of Kelly, such as half, to reduce variance, since full Kelly is the mathematically optimal long-run growth rate but comes with large short-term swings. This is a general sizing choice, not a TheRundown-specific feature. ### Is +EV betting guaranteed to make money? No. EV is an average over many bets, not an outcome of any single one. A well-priced +EV bet can still lose, and the no-vig estimate is only as good as the books that fed it.