Why the 0 baseline keeps tripping up otherwise-smart bettors
The first UFC card I tracked seriously was UFC 229 — Khabib vs McGregor, October 2018. I was using decimal odds at the time, because I had come up on European football betting, and I remember staring at a US sportsbook screen showing “McGregor +180 / Khabib -220” and doing arithmetic in my head three different ways before I understood what I was looking at. The problem was not that American odds are complicated. The problem is that they are built around a $100 stake unit that nobody told me was the unspoken anchor.
That is the trap I want to get you out of in this article. American odds in MMA are not harder than decimal or fractional odds — they are just denominated differently. Once you internalise the $100 baseline, you can read a UFC slip faster than most decimal users can do the equivalent mental conversion. The catch is that the $100 baseline is invisible in the notation, which is why so many newcomers misprice their first few bets.
So this piece is going to walk through plus/minus mechanics, implied probability, the way the vig hides inside a two-sided line, and a worked example using a real UFC matchup. By the end, you should be able to look at any UFC moneyline and tell me in three seconds what the book thinks the probability of each fighter winning actually is.
See also: UFC parlay payout math for multi-leg calculations.
Plus and minus, properly translated
A minus number tells you how much you need to stake to win $100. A plus number tells you how much you win on a $100 stake. That is the entire mechanic. Everything else follows from it.
So if you see Islam Makhachev at -300 against Arman Tsarukyan at +240 on a UFC moneyline, the book is asking you to risk $300 to win $100 on Makhachev, or risk $100 to win $240 on Tsarukyan. The $100 in both cases is the unit of measurement, not your required stake. You can scale up or down freely — a -300 bet of $30 wins $10, a +240 bet of $25 wins $60. The proportions hold.
What the notation is really showing you is the cost of certainty against the cost of contrarianism. A bigger negative number means the book is asking more from you to back the favourite. A bigger positive number means the book is offering more to whoever is willing to back the underdog. The notation collapses the favourite/underdog distinction into a single sign convention, which is elegant once you see it but confusing on first contact.
One thing I want you to internalise from the start: there is no “fair” reading of plus/minus odds without doing the implied-probability conversion. The numbers as printed are not probabilities. They are payout ratios that contain probabilities. Confusing the two is the single most common mistake I see in newer UFC bettors.
Implied probability — the formula that ends the guesswork
If you remember nothing else from this article, remember the two implied-probability formulas. Negative odds: implied probability equals the absolute value of the odds, divided by the absolute value plus 100. So -250 becomes 250 / (250 + 100) = 71.4%. Positive odds: implied probability equals 100 divided by the odds plus 100. So +200 becomes 100 / (200 + 100) = 33.3%.
That is it. Two formulas, both giving you the percentage of the time the book is implying the relevant outcome will occur, before accounting for the book’s margin. Run them on every UFC line you see and you will start to feel the prices instead of just reading them. A fighter at -110 has an implied probability of 52.4%. At -150, the implied probability jumps to 60%. At -200, it is 66.7%. At -400, it is 80%. At +120, it is 45.5%. At +250, it is 28.6%.
What I find changes for most bettors when they start running these conversions habitually is that the difference between, say, -135 and -160 stops feeling like a small line move. -135 implies 57.4%, and -160 implies 61.5%. That is a four-percentage-point swing in implied win probability for what looks superficially like a minor shift. UFC lines are tight markets, and small notation moves carry big probability moves. The conversion lets you see it.
One more habit worth building: when you look at a two-sided UFC moneyline, run the conversion on both sides and add them up. The total should be more than 100%. That excess over 100% is the book’s hold, and it is the next thing to understand.
Where the vig hides — hold and how to remove it
The reason a two-sided moneyline sums to more than 100% is that the book is not offering you a fair coin flip. It is offering you a coin flip with a built-in margin. That margin goes by several names — vig, juice, hold, or simply “the take.” All four describe the same mechanic: the book has built a small overround into the line so that, on balanced action, it makes money regardless of which fighter wins.
Take a clean example. Two evenly matched fighters, both listed at -110. Implied probability of each is 52.4%. Add them: 104.8%. The 4.8% excess is the hold. On a balanced market with $100 on each side, the book takes in $220, pays out $210 to the winning side ($100 stake plus $110 win), and keeps $10. That $10 on $220 of action is roughly 4.5% — the operational hold the book is targeting.
To remove the hold and find the “no-vig fair line,” you divide each side’s implied probability by the total. So in the -110/-110 example, each side’s no-vig fair probability is 52.4 / 104.8 = 50%, which is what you would expect for evenly matched fighters. That conversion becomes more interesting when the line is lopsided. Fighter A at -350 (77.8%) and Fighter B at +260 (27.8%) sums to 105.6% hold. The no-vig fair probabilities are 73.7% for the favourite and 26.3% for the underdog — a notable adjustment from the raw implied numbers.
This is the gateway to value-bet analysis. If you have a fundamentals-based view that Fighter B should win, say, 32% of the time, and the no-vig fair line says the book is implying 26.3%, then +260 is offering you actionable edge. If you just looked at the raw +260 (27.8% implied) and your view (32%), the gap would still be there but you would be reading the book’s intent wrong. The no-vig step matters.
A worked example from real betting practice
Let me walk you through a real lightweight matchup that surfaces well in MMA-betting tutorials: Justin Gaethje at +135 against Rafael Fiziev at -160. This is a clean two-sided moneyline with no special pricing wrinkles, and it teaches every step we have covered so far.
Step one — translate the payouts. Gaethje at +135 means a $100 stake wins $135 (returning $235 total). Fiziev at -160 means a $160 stake wins $100 (returning $260 total). Cheap mental math: if you put $100 on each side, you can lose either $100 or $160 depending on who wins.
Step two — convert to implied probability. Gaethje at +135: 100 / (135 + 100) = 42.6%. Fiziev at -160: 160 / (160 + 100) = 61.5%. Add: 104.1%. The hold on this line is about 4.1%, which is below the typical UFC moneyline hold (most US-facing books run 4.5–5.5% on flagship cards, with offshore books occasionally lower on early lines and tighter on closing lines).
Step three — remove the vig. Gaethje no-vig fair: 42.6 / 104.1 = 40.9%. Fiziev no-vig fair: 61.5 / 104.1 = 59.1%. The book is implying Fiziev wins this fight just under 60% of the time, with Gaethje at just over 40%. That gives you a much cleaner target for comparison against your own pre-fight model.
Step four — sanity check. Does the no-vig fair line feel reasonable for the matchup? A 60/40 split in a striker-vs-striker lightweight fight where one fighter has higher output and the other has higher one-shot power is plausible. If you think Gaethje wins this 45% of the time — slightly more than the no-vig fair line implies — then +135 is a small positive-expected-value bet. If you think Gaethje wins 38% of the time, then +135 is slightly underpriced for you, and the bet is negative-EV. The math becomes the framework. Your fight read becomes the input.
If you want to take this further — into method-of-victory pricing, parlay math, total-rounds calculations and the rest of the UFC bet-type stack — I have a full breakdown in my guide to UFC bet types and how the markets are structured.
Converting between formats without losing your read
Sometimes you will need to flip between American, decimal and fractional odds — especially if you are watching offshore books, which often default to decimal, or reading European MMA media that uses fractional. The conversions are mechanical, but learning them locks in your fluency.
American to decimal: for negative American odds, decimal = (100 / absolute value of odds) + 1. So -200 becomes (100/200) + 1 = 1.50. For positive American odds, decimal = (odds / 100) + 1. So +200 becomes 3.00. Quick check — both of those should imply 33.3% and 33.3% respectively, and 1 / 1.50 = 66.7% (the favourite) while 1 / 3.00 = 33.3% (the underdog). Decimal odds are the most direct of the three formats: the implied probability is just 1 divided by the decimal odd, full stop.
American to fractional: -200 becomes 1/2 (you risk two to win one). +200 becomes 2/1 (you risk one to win two). Fractional is the most intuitive for small bets and the most awkward for tight UFC favourites. Fiziev at -160 in fractional is 5/8, which nobody finds pleasant. This is part of why American odds dominate US MMA coverage despite their $100-baseline awkwardness — fractional gets ugly fast on heavy favourites.
The format you choose matters less than the consistency of your conversions. I work primarily in American because most of the markets I cover quote that way, but I always cross-check implied probability the same way regardless of format. That habit is what separates someone who “reads odds” from someone who actually understands what the line is telling them.
See also: how to bet on ufc in california — reading odds.
Where the work pays off in your week
Reading American odds fluently buys you something specific: it makes line shopping useful instead of theoretical. If you can convert -250 to 71.4% in your head and -230 to 69.7% in your head, then the choice between two books offering those prices stops being an abstract preference and becomes a concrete 1.7-percentage-point difference in implied probability. Over a UFC season, that kind of differential — compounded across many fights and the cleaner read on hold — is what divides a thoughtful bettor from someone who treats every moneyline as roughly equivalent. The notation is not the obstacle. The notation, once decoded, is the lens.
