NBA
MLB01 · The cost of doing business
Vigorish is rent
Vigorish — the vig, the juice, the hold — is the commission a sportsbook bakes into a price so it profits regardless of which side wins. On a standard -110 / -110 market you risk $110 to win $100 on either side. If a book balanced $110 on each side and paid out the winner, it collects $220 and returns $210. The $10 it keeps on $220 of handle is the rent: 4.76%.
That is why beating sports betting is not a coin-flip problem. You are not trying to win 50% of your bets; you are trying to win more often than the price implies after the rent is stripped out. Everything downstream — fair lines, edge, expected value — is just bookkeeping on that one idea.
02 · From odds to probability
Implied probability
Implied probability is the win rate a price assumes. American odds convert with two formulas — one for favorites (negative), one for underdogs (positive).
A -110 favorite implies 110 / 210 = 52.38%. A +120 underdog implies 100 / 220 = 45.45%. Add the two sides of a -110 / -110 market and you get 52.38% + 52.38% = 104.76%. That total is the overround: it sums to more than 100% precisely because the vig is the extra 4.76%.
03 · Removing the rent
De-vigging to a fair line
De-vigging removes the commission so both implied probabilities add back to exactly 100%. The everyday method is proportional (multiplicative): divide each side’s implied probability by the overround.
For the -110 / -110 market: 52.38% / 104.76% = 50.00%each side. The vig vanishes; the fair line is a true coin flip. There are sharper de-vig methods — the additive (equal-margin) and power (Shin) methods correct for the fact that favorites and longshots don’t carry vig identically — but proportional is the workhorse and the right place to start.
04 · The whole point
Edge = price minus fair
Once you have a fair probability, your edge is the gap between what you believe (or what the sharpest consensus believes) and what the price you can actually bet implies. If a bet’s fair win probability is higher than the implied probability of the best available price, the difference is positive expected value.
Worked example · NBA rebounds prop
You’re looking at a center’s rebounds line at 24.5. The two sides are priced Over -105 / Under -115.
The fair line says the Over hits 48.92% of the time — call the true line 25.0. Now suppose your model projects the player at 25.2 rebounds, nudging the true Over probability to about 49.7%. Your edge on the Over is 49.7% − 48.91% ≈ +0.8%. Thin, real, and only visible because you de-vigged first.
05 · Turning edge into dollars
The EV expectation
Expected value is what a bet returns on average if you could place it infinitely many times. Multiply each outcome by its probability and add them up.
Worked example · A $100 bet at -110 with a real edge
You bet $100 on the Over at -110, which pays $90.91 profit on a win. Your de-vigged work says the true win probability is 53% — a genuine edge over the 52.38% the price implies.
That’s a +1.18%return per bet. It looks like nothing. Across a thousand disciplined plays at the same edge, it’s the entire game — which is also why how much you stake matters as much as whether the edge exists. That’s the Kelly staking problem.
06 · Try it
Odds converter & de-vig calculator
Drop in any two-way market. It converts each price to implied probability, shows the overround and the hold, and de-vigs to a fair line in real time.
Live · De-vig calculator
Fair probabilities are the two implied prices scaled so they sum to 100% — the vig removed proportionally from each side.
07 · The honest part
When EV breaks down
The math is exact. The inputs are not. Expected value is only as good as your win-probability estimate, and that estimate is shakiest exactly where it’s tempting to trust it:
- Thin markets. A prop only two books quote has no consensus to de-vig against — the “fair” line is one book's opinion.
- Volatility shocks. Injuries, ejections, blowout benchings, and weather can swing an outcome the model never priced.
- Stale lines. An edge that looks like +6% is usually a number the book hasn't moved yet — and won't honor at your stake.
- Correlated legs. Stacking props from one game compounds variance; the single-bet EV math no longer describes the parlay.
On those, the right move is to size down or pass. A fair line you can’t trust is a guess wearing a decimal point. Shop the lowest-vig price you can find — every basis point of hold you avoid is edge you keep — and confirm the number is live before you fire.
Reference
Frequently asked
Why don't you just publish the no-vig fair lines?
A fair line is a probabilistic estimate, not a decree — it shifts every time the market reprices, which on a liquid game is constantly. Dynatyze recomputes the de-vigged fair line on every refresh and shows it next to the best available price so you see the gap as it exists right now, not a stale snapshot that's already wrong.
Can I spot a +EV edge just by looking at the odds?
No. Positive expected value is the gap between a price and a fair line you can't see with the naked eye, and that gap is usually a fraction of a percent. You either run the de-vig math yourself or let a tool do it — eyeballing -115 vs -110 will not tell you which side carries the edge.
What size edge is worth betting?
A real, repeatable edge above the noise floor is usually 1% to 3% of expected value after de-vigging; anything north of 5% deserves a second look for a stale line or a number you've misread. Edge is probabilistic, so a 3% edge still loses plenty of individual bets — it only compounds across a large number of plays.
When does the expected-value math stop working?
Expected value assumes your win probability is well-estimated, which breaks down on thin or volatile markets — a freshly posted prop, a player one tweet away from being scratched, or a market with two books quoting it. On those, the fair line is a guess dressed up as a number, and the honest move is to size down or pass.
Does de-vigging assume both sides are equally sharp?
Standard two-way de-vigging splits the hold evenly across both sides, which assumes the market is equally efficient on the over and the under. When one side is a public magnet and the other is where the sharp money sits, that assumption skews the fair line, and a more advanced de-vig (or a sharper reference book) is the correction.
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Research and methodology only. Dynatyze is not a sportsbook and takes no wagers. Bet legally and within your means.