Vig is the silent tax that decides if you win long-term
You can pick winners and still lose money. That’s not some motivational poster. It’s basic math.
The reason is vig (also called juice): the sportsbook’s built-in fee. Books don’t need you to go 50/50. They need you to go 50/50 while paying a toll every time you bet.
Think of it like buying and selling a stock with a spread. If you buy at $10.10 and sell at $9.90, you can be “right” on direction and still bleed from the gap. Sports betting has the same idea. The gap is vig.
Break-even probability is the win rate you need to not lose money at a given price. If you bet -110 (typical point spread), you don’t break even at 50%. You need to win more than that because you’re risking $110 to win $100.
This is where recreational bettors get crushed: they obsess over “I win 55%” without asking, “55% at what price?” Because two bettors can win 55% and have totally different long-term results if one is laying -120 all day and the other is grabbing +105s and +110s when the market hands them out.
Once you learn to spot break-even price fast, you stop thinking like a fan and start thinking like a trader. You’re not “betting teams.” You’re buying prices.
Odds 101: American odds and what they really mean
Let’s define the jargon the right way, from scratch.
American odds are the -110, +150 style numbers you see on most U.S. books.
- Negative odds (like -110): how much you must risk to win $100 profit.
- Positive odds (like +150): how much profit you win on a $100 risk.
Examples:
- -110: risk $110 to win $100 (you get $210 back total if you win: your $110 stake + $100 profit).
- +150: risk $100 to win $150 (you get $250 back total if you win).
Implied probability is the win rate those odds are “pricing in.” It answers: “What percentage of the time would this bet need to win for the book to break even at that price?”
Here are the conversions you need (memorize these or keep them handy):
- For negative odds (-A): implied probability = A / (A + 100)
- For positive odds (+A): implied probability = 100 / (A + 100)
Do one quick example of each:
- -110: 110 / (110 + 100) = 110/210 = 52.38%
- +150: 100 / (150 + 100) = 100/250 = 40%
That’s the first “aha.” A coin-flip bet priced at -110 isn’t a coin flip anymore. You need 52.38% just to tread water.
Once you can turn odds into percentages in your head (or close), you stop getting hypnotized by the numbers. You start seeing what matters: the required win rate.
Break-even probability: the fastest way to know if a price is trash
Break-even probability is just implied probability viewed from your side. It’s the win rate you need to break even at that exact price.
So if a book deals you -110, your break-even is 52.38%. If your true win probability is 52%, you’re not “basically even.” You’re negative. Slightly negative still adds up to a lot of damn money over hundreds of bets.
Here are break-even numbers you’ll see constantly:
- -105 → 105/205 = 51.22%
- -110 → 110/210 = 52.38%
- -115 → 115/215 = 53.49%
- -120 → 120/220 = 54.55%
- +100 → 100/200 = 50%
- +105 → 100/205 = 48.78%
- +110 → 100/210 = 47.62%
That’s why line shopping matters even when the difference looks tiny. Going from -115 to -105 drops your break-even from 53.49% to 51.22%. That’s a 2.27% swing in required win rate for the exact same pick.
And yes, 2% is enormous in betting. Most people would kill for a sustainable 2% edge. Meanwhile they donate 2% by clicking the first number they see.
If you want a simple rule: every 5 cents of juice matters. -110 vs -115 vs -120 is the difference between “maybe profitable” and “dead on arrival” for a lot of bettors.
Removing the vig: how to find “true odds” from a two-way market
The book’s implied probabilities include vig. That means if you convert both sides of a typical two-way market (like spread or moneyline with no draw), the probabilities add up to more than 100%.
That extra is the sportsbook’s edge.
Example: NFL spread, both sides priced at -110.
- Team A -110 → 52.38%
- Team B -110 → 52.38%
- Total = 104.76%
That extra 4.76% is the “overround” (the built-in cushion). To estimate the vig-free or true probabilities, you normalize them back down to 100%.
Vig-free probability (two-way market) = implied prob / (sum of implied probs)
For the -110/-110 example:
- Sum = 0.5238 + 0.5238 = 1.0476
- True P(Team A) = 0.5238 / 1.0476 = 0.50
- True P(Team B) = 0.5238 / 1.0476 = 0.50
That makes sense: a fair coin would be +100 / +100 (50/50), but the book sells it to you at -110/-110.
Let’s do a less symmetrical example where you’ll actually use this.
Say an NBA moneyline is:
- Lakers -150
- Opp +130
Convert to implied probabilities:
- -150 → 150/(150+100) = 150/250 = 60%
- +130 → 100/(130+100) = 100/230 = 43.48%
- Total = 103.48%
Remove vig:
- True P(Lakers) = 0.60 / 1.0348 = 58.0%
- True P(Opp) = 0.4348 / 1.0348 = 42.0%
So the market’s “true” opinion is closer to 58/42, not 60/43.5. That difference is the toll.
The simple example: same win rate, totally different profit
You want the cleanest illustration of why vig matters? Here it is.
Two bettors both hit 55% on spread bets over 1,000 wagers. Same picks. Same win rate. The only difference is price.
Bettor A always lays -110.
Bettor B line shops and averages -105.
Assume $100 to win format for easy math (so at -110 you risk $110 to win $100; at -105 you risk $105 to win $100).
Bettor A (-110):
- Wins: 550 × $100 = $55,000 profit
- Losses: 450 × $110 = -$49,500
- Net: +$5,500
Bettor B (-105):
- Wins: 550 × $100 = $55,000 profit
- Losses: 450 × $105 = -$47,250
- Net: +$7,750
Same 55%. Bettor B makes $2,250 more just by paying less vig. No extra “handicapping skill.” No secret system. Just not donating cents.
Flip it around and it gets uglier.
If you average -120 instead of -110 at the same 55%:
- Losses: 450 × $120 = -$54,000
- Net: $55,000 - $54,000 = +$1,000
You’re still hitting 55% and barely winning. That’s how people end up saying “I pick winners but I don’t make money.” They’re not lying. They’re just overpaying.
Your 10-second method: convert, strip vig, compare across books
You don’t need a spreadsheet addiction. You need a repeatable routine you can do quickly.
Step 1: Convert the odds you’re offered into implied probability.
Use the formulas:
- -A → A/(A+100)
- +A → 100/(A+100)
Step 2: If you’re comparing “true odds,” remove vig using both sides.
Take each side’s implied probability and divide by the total.
Step 3: Compare your book’s price to the vig-free probability (or to another book’s price).
If your book is offering a probability lower than the market’s true probability (meaning better payout), you’re in business.
Concrete example across two books on the same game (two-way market):
Book 1: Bears -3 (-110) / Vikings +3 (-110)
Book 2: Bears -3 (-105) / Vikings +3 (-115)
First, find the “true” market from Book 2 (since it’s a more efficient split sometimes, but either works):
- Bears -105 → 105/205 = 51.22%
- Vikings -115 → 115/215 = 53.49%
- Total = 104.71%
- True P(Bears) = 51.22 / 104.71 = 48.90%
- True P(Vikings) = 53.49 / 104.71 = 51.10%
Now compare the price you can get.
If you want Bears +3, Book 2 offers -105, which is break-even 51.22%. But the vig-free probability says Bears should cover about 48.90% (from that book’s own market). That’s not value. You’re paying too much.
If you want Vikings +3, Book 1 offers -110 (52.38% break-even). True probability says 51.10%. Still not great.
This is the mindset: you’re not asking “who wins?” first. You’re asking “what’s the fair price, and am I beating it?”
If you want help applying this to specific bets without doing the math every time, the Betting Assistant is built for exactly this kind of “what win rate do I need at this price?” thinking. And if you’re scanning multiple books trying to find where the payout beats the market, the Positive EV Finder does the heavy lifting by comparing prices across sportsbooks.
Where bettors screw this up (and how you avoid it)
You’ll understand vig and still mess it up if you fall into the usual traps.
1) You compare odds without comparing the whole market.
Taking +105 instead of +100 is good, but you also want to know if the market itself is efficient or shaded. Removing vig (normalizing probabilities) keeps you honest.
2) You ignore that different bet types carry different vig.
Player props and same-game parlays often have fatter margins than major sides/totals. That doesn’t mean “never bet props.” It means you better demand a better price because the toll is higher.
3) You treat line movement like magic instead of math.
When a line moves from -110 to -125, the required win rate jumps from 52.38% to 55.56%. That’s not trivia. That’s your edge getting taxed away in real time. If you want to get better at reading moves without chasing fake narratives, read Trap or Steam? 4 Patterns That Fake Sharp Action.
4) You think parlays “beat the vig.”
Most parlays are sucker bets because you multiply vig across legs and add correlation tricks the book prices better than you do. If you love parlays, fine—just understand you’re paying for the entertainment.
5) You don’t line shop because it feels small.
Five cents here, ten cents there… it’s death by a thousand cuts. Over a season, it’s the difference between a profitable handicapper and a frustrated one.
If you want more foundational stuff like this, the education hub at /blogs/education/ is where we keep the “how betting actually works” posts.
Responsible gambling: Bet within your limits and treat sports betting like a high-variance investment, not a paycheck. If it stops being fun, take a break.
