---
title: "Favorite-Longshot Bias Explained: Why Longshots Cost More Than They Pay"
canonical: "https://0xinsider.com/learn/favorite-longshot-bias-explained"
datePublished: "2026-09-12"
dateModified: "2026-09-12"
description: "What the favorite-longshot bias is, why bettors overpay for big payouts, how to test a market for it, and where it shows up in 411,770 Polymarket sports bets: only under 10 cents."
---

# Favorite-Longshot Bias Explained: Why Longshots Cost More Than They Pay

Last updated: 2026-09-12
Canonical: https://0xinsider.com/learn/favorite-longshot-bias-explained

The favorite-longshot bias is the finding that bettors pay too much for long odds and too little for short ones, so longshots return less per dollar than favorites. It has held at racetracks since 1949 and at every sportsbook since. This guide explains the bias, the reasons behind it, how to test a market for it, and what happens when the crowd sets the price on an order book: on Polymarket sports markets it survives only below 10 cents.

## What the favorite-longshot bias is

Take every bet ever placed at a venue and sort it by the odds. Then check how often each group of bets actually won. In a fair market, bets at 10% implied probability win 10% of the time and bets at 80% win 80% of the time. In every racetrack and sportsbook dataset published since Richard Griffith's 1949 study, they do not. Bets at long odds win less often than their price says and bets at short odds win more often.

The consequence is in the return. Because the house margin applies to everything, both groups lose money on average, but longshots lose far more. A typical racetrack finding is that favorites return about 95 cents on the dollar while horses at 100 to 1 return 20 or 30 cents. At a sportsbook the pattern is gentler but the same shape: heavy favorites come close to break-even before the vig, and big underdogs and long parlays lose several times the vig.

That is the whole bias. Longshots are overpriced relative to how often they win. Favorites are underpriced. The chart below draws the shape as those studies report it, beside a fair line and beside the measured line from Polymarket sports markets, which this guide comes back to.

## A worked example at +900

A +900 underdog carries an implied probability of 10%. If the bias is at work and the underdog actually wins 7% of the time, a $100 bet returns $900 seven times in a hundred and loses $100 the other 93. That is $6,300 won against $9,300 lost, a return of minus 32 cents on the dollar. The bettor believed they were paying 10¢ for a 10% chance; they were paying 10¢ for a 7% chance.

Now the favorite on the other side. If the underdog is really 7%, the favorite is really 93%, and a sportsbook offering it at -900 is charging 90% for a 93% outcome. Before the vig, that is a profitable bet: $100 wins $11.11 ninety-three times and loses $100 seven times, plus $333 on $10,000 staked, a 3.3% return. After a typical vig it is roughly break-even, which is what the studies find for heavy favorites.

The example is arithmetic, not a claim about any real game. It shows what the bias means in dollars: the same misjudgment of a probability costs the longshot bettor a third of their stake and hands the favorite bettor a small edge.

## Why it happens

The most-tested explanation is that people overweight small probabilities. A 3% chance feels like more than 3%, so a payout at 33 to 1 feels like a better deal than it is. The effect shows up in lotteries, in insurance and in every experiment that asks people to price a small chance of a big outcome, and betting is one long series of those experiments.

The second is a taste for the payout itself. A bettor with $20 and an evening to fill gets more from a 20 to 1 shot that might pay $400 than from a favorite that might pay $22, and is willing to accept a worse price for it. Sportsbooks know this and price parlays and long underdogs accordingly, which is why the bias is steepest in the products that offer the biggest multipliers.

The third is who bets what. Informed bettors, the ones with a model or an edge, tend to find their value in favorites and mid-priced outcomes, where a small misprice on a large probability is worth trading. Casual bettors gravitate to longshots. So the longshot price is set by the less informed side of the market, and the favorite price by the more informed side. This is also the reason a bookmaker can shade longshots further without losing sharp business.

None of these needs a bookmaker to exist. The first two are about the bettor. If they are the cause, a market with no house line should show the bias too.

## How to test for it

Sort the bets by the price paid into buckets, ten cents wide is standard, and for each bucket compare two numbers: the average price paid and the share of bets that won. Their difference, in percentage points, is the edge for that bucket. A fair market has every bucket near zero. The bias shows as negative edge at the cheap end and positive edge at the expensive end.

Report the dollar return as well. Edge in points understates the longshot problem: a 7¢ contract that wins 4% of the time is only three points mispriced, but it returns 57 cents on the dollar. Dollar return, stake-weighted and held to settlement, is the number a bettor feels.

Then check the confidence intervals, and cluster them by event rather than by bet. Five hundred bets on one longshot that comes in are one bet that came in. A study that treats them as five hundred independent observations will find a profitable longshot bucket that is one tournament, and the next section has exactly that example. You need thousands of bets per bucket and many events per bucket before the shape means anything.

## What Polymarket sports markets show

Polymarket sports markets have no bookmaker. A contract pays $1 if the team wins, and the price is set by buyers and sellers on an order book. 0xinsider ran the test above on 411,770 buys of $1,000 or more across every Polymarket sports market that settled between April 2 and September 11, 2026: soccer, esports, the NBA, tennis, baseball, hockey, cricket, MMA and the WNBA.

Across the whole sample buyers paid 60.6¢ and won 60.7% of the time. Bucket by bucket, buys from 20¢ to 98¢ sat within a point and a half of their price, with confidence intervals that include zero. Buyers at 80 to 90¢ paid 84.7¢ and won 84.3%. Buyers at 40 to 50¢ paid 45.4¢ and won 45.8%. The market was calibrated, which is a different result from every sportsbook study.

The 10 to 20¢ bucket shows a dollar return of plus 27.6%, and it is the clustering lesson from the last section. One market, Spain to win the 2026 World Cup, drew 490 large buys at an average of 15.2¢ and paid out $41.3 million when Spain won. The rest of the bucket, 1,555 markets, lost $15.4 million between them. The bucket's confidence interval runs from minus 5.6 to plus 19.1 points, and the honest reading is zero. The study is at 0xinsider.com/research/favorite-longshot-bias-polymarket-sports.

## Under 10 cents

The one bucket where the textbook bias appears in full is the cheapest. Buys under 10¢ paid 6.49¢ on average and won 2.97% of the time: minus 3.52 points, with an interval from minus 5.50 to minus 0.28 that clears zero. Those 2,020 buys put $28.2 million into contracts and got back $11.1 million. A dollar staked returned 39 cents.

In five-cent steps it is worse at the bottom. Buys between 2 and 5¢ paid 3.19¢ and won 0.97%. Buys between 5 and 10¢ paid 7.62¢ and won 3.66%, a return of 32 cents on the dollar. From 10¢ upward the second bar catches the first.

This is the bias without the bookmaker. Nobody shaded these prices. Buyers with $1,000 or more to stake chose to pay 7¢ for outcomes that arrived one time in twenty-seven, because 7¢ buys a fourteen-to-one payout and fourteen to one is the number they were buying. The explanation from the earlier section, that people overweight small probabilities and enjoy the size of the payout, is sufficient on its own.

## The favorite side of the bias

At a sportsbook, favorites are the better of two bad bets: still negative after the vig, but far less negative than longshots. On Polymarket sports markets, favorites are not a bad bet before fees at all. Buys at 80 to 90¢ returned plus 0.36% on the dollar and buys at 90 to 98¢ minus 0.60%. Buys at 70 to 80¢ returned plus 3.58% across 49,123 buys.

Split by sport, favorites at 70¢ and up were calibrated in soccer, tennis, esports, hockey and cricket and slightly negative in the NBA and baseball. MMA was the exception: fight favorites paid 80.4¢ and won 61.2% of the time, minus 19 points, and two UFC upsets carried most of the loss. MMA has 344 settled markets in the sample against 11,653 for soccer, so one card moves the whole sport. It is a lesson about small samples more than about fighters.

The fee does what the vig does, but smaller and visible. Polymarket's sports taker fee at 90¢ is 0.5% of the stake and at 95¢ is 0.25%; a resting limit order pays none. A favorite that returns minus 0.6% before fees returns about minus 1.1% after them for a taker. A sportsbook favorite at the same probability carries the full 4.55% hold.

## Sports against the rest of Polymarket

The calibration in sports is not a property of the platform. Run the same buckets over large buys on politics, crypto, geopolitics, culture, finance, world and business markets in the same window and buyers miss the price by six to ten points in most buckets, always against themselves. Buyers at 90 to 98¢ on those markets paid 94.1¢ and won 84.4% of the time.

Those markets are thinner, settle over months rather than hours, and a surprising summer in politics moves every bucket at once, so the comparison says less about mispricing in the abstract than about where a large buyer's price has matched the result. In sports it has. That is consistent with the third explanation above: sports markets on Polymarket are deep, trade constantly, and attract the informed side of the market on both ends of the price.

## What to do with it

Do not buy the contract under 10¢ because of the payout. In this sample it was the worst bet on the platform by a wide margin, and the reason it was bad is the reason it was tempting. If you believe a 5¢ outcome is really 10%, that is a bet; if you want the twenty-to-one, that is a lottery ticket at a bad price.

Stop expecting a favorite premium. At a sportsbook, backing heavy favorites is a way to lose less. On a Polymarket sports market the favorite is priced at its probability, so it is neither a way to lose less nor a way to win. Your edge has to be a probability the market has not yet priced, or a counterparty who is wrong.

And test any market you bet in before you trust a rule from another one. The bias is a fact about bettors, and it appears wherever the bettors buying longshots outnumber the ones selling them. It disappears where the market is deep enough that informed money prices both ends. The same test that found it under 10¢ on Polymarket found nothing above, and a bettor who assumed the sportsbook shape would have been fading favorites that were fairly priced.

## How 0xinsider shows it

Every Polymarket wallet has a public record, and 0xinsider grades it on the gap between the prices it paid and how often it won, the same measure this guide uses for a bucket. On a trader profile that is the calibration edge, beside the win rate and the average entry price, so you can see whether a wallet's record is skill or a taste for favorites. The leaderboard at 0xinsider.com/leaderboard ranks wallets by it.

On each sports board, 0xinsider.com/sports/soccer, 0xinsider.com/sports/nba, 0xinsider.com/sports/ufc and the rest, the sharp money strip shows which side the profitable wallets are on for each game and how much they have on it. When the well-graded wallets are on the 15¢ side, that is a longshot with informed company. When they are absent, the price is what it says. The whale alerts feed at 0xinsider.com/whale-alerts shows each large buy as it lands with the buyer's grade beside it, which is where the 7¢ buys in this guide came from.

## Frequently Asked Questions

What is the favorite-longshot bias? The finding, first published from racetrack data in 1949 and repeated at every sportsbook since, that bets at long odds win less often than their price implies and bets at short odds win more often, so longshots return less per dollar than favorites.

Why do bettors overpay for longshots? People overweight small probabilities, so a 3% chance feels like more than 3%. Many bettors also value the size of a possible payout for its own sake. And longshot prices are set mostly by casual bettors while favorite prices are set by informed ones, which lets a bookmaker shade the longshot further.

Does the favorite-longshot bias exist on Polymarket? Only under 10 cents. Across 411,770 Polymarket sports buys of $1,000 or more from April to September 2026, buys under 10¢ won 2.97% of the time at an average price of 6.49¢ and returned 39 cents on the dollar. Every bucket from 20¢ to 98¢ was within a point and a half of its price.

Are favorites a good bet because of the bias? At a sportsbook, heavy favorites lose less than longshots but still lose to the vig. On Polymarket sports markets, favorites at 80¢ and up returned between plus 0.4% and minus 0.6% on the dollar before fees, so they carry no premium and no penalty.

How do I test a market for the bias myself? Sort bets into price buckets, compare the average price paid to the share that won, report the dollar return as well as the point gap, and cluster confidence intervals by event rather than by bet. One longshot that comes in with hundreds of bets on it can make a whole bucket look profitable.