What Is Expected Value in Sports Betting?
- Ronald Lockington
- Sep 25, 2024
- 6 min read
Updated: Mar 24
Expected value definition
Expected value (EV) is the average long term return of a bet based on your estimated win probability and the sportsbook’s payout. If the EV is positive, the bet is profitable over time.
Thinking about it another way, EV is the average profit or loss you would expect from a bet if you could place that same bet many times at the same odds and true win probability.
Expected value measures whether a bet is worth making based on two things:
Your estimated probability of winning
The payout offered by the sportsbook
A bet can win today and still be a bad bet. A bet can lose today and still be a good bet. Expected value helps you judge the quality of the price, not just the outcome of one ticket.
Expected value formula
The general expected value formula is:
E(x) = x1p1 + x2p2 + ... + xnpn
In sports betting, the simpler version is:
EV = (Win Probability × Decimal Odds) − 1
Where:
Win Probability is your estimated true chance of winning
Decimal Odds are the sportsbook odds converted to decimal format
If EV is greater than 0, the bet has positive expected value.
If EV is less than 0, the bet has negative expected value.
Simple example
Imagine you think a player prop has a 58% chance to win, and the sportsbook is offering -110 odds.
First, convert -110 to decimal odds:
1.9091
Then plug it into the formula:
EV = 0.58 × 1.9091 − 1 = 0.106
That means the bet has an expected value of +10.6%.
In plain English, for every dollar staked on this same type of edge over time, you would expect to earn about 10.6 cents on average.
What is value betting?
In sports betting, value betting means placing bets where your estimated chance of winning is higher than the sportsbook’s implied probability.
For example:
If a team really has a 55% chance to win
But the sportsbook price implies only 50%
You have found value
That does NOT mean the bet will win tonight. It means the price is in your favor over a large sample.
This is why sharp bettors care so much about expected value. It's the clearest way to separate good prices from bad prices.
Why expected value matters in sports betting
Most losing bettors think in terms of picks (whether they chose the "right" side). Winning bettors think in terms of price.
A sportsbook can hang a line on the winning side but still offer the wrong price. That's where value lives.
Expected value matters because it helps you:
Judge whether a bet is profitable
Compare bets across different markets
Avoid emotionally driven wagers
Stay focused on long term edge instead of short term results
Without EV, betting becomes guessing. That's why most bettors lose.
Why many bettors ignore EV
A lot of bettors don't make decisions based on expected value. They bet based on comfort, excitement, or fear.
Two concepts help explain that behavior.
Prospect theory
Prospect theory says people tend to feel losses more strongly than equivalent gains.
In sports betting, that often shows up as:
Laying bad prices on favorites because they feel safer
Avoiding underdogs even when the number is good
Chasing parlays because the upside feels exciting
This helps explain why many bettors choose wagers that feel good instead of wagers that are actually profitable.
Utility theory
Utility theory says people don't always try to maximize dollars. Sometimes they try to maximize enjoyment.
That means a bettor may rationally choose:
A fun same game parlay
A longshot futures bet
A smaller, safer payout
There's nothing inherently wrong with that. But it's different from profit seeking and value betting.
If your goal is entertainment, utility can guide your choices, and that's fine.
If your goal is profit, expected value has to come first.
How to calculate expected value in sports betting
A practical process in real-world betting looks like this:
1. Remove the vig
Sportsbook odds include margin. Before you judge a price, estimate the fair probability.
Use a No Vig Calculator to strip out the juice.
2. Estimate true win probability
This can come from:
Your model
Your projections
Historical data
Injury and news analysis
Market based estimation
3. Convert the odds
Convert American odds into decimal odds so you can run the EV formula cleanly.
Use an Odds Converter if needed.
4. Calculate EV
Plug your probability estimate and decimal odds into the formula:
EV = p × Decimal Odds − 1
5. Compare sportsbooks
A small price difference can turn a bad bet into a good one.
For example, a bet that's negative EV at -115 might become positive EV at +100. That's why line shopping matters so much.
Use an odds screen to speed up line shopping.
6. Size your bet properly
Expected value tells you whether to bet. It doesn't tell you how much to bet on its own.
For sizing, use a Kelly Calculator. Many bettors use fractional Kelly, such as one quarter Kelly or half Kelly, to reduce risk and variance.
Quick betting examples
Example 1: Coin flip at -105
If the true chance is 50% and the sportsbook offers -105, decimal odds are 1.9524.
EV = 0.50 × 1.9524 − 1 = -0.0238
That's -2.38% EV.
Even though the bet feels close to fair, it's still negative expected value.
Example 2: Player prop at -110
If your projection says the prop wins 58% of the time and the sportsbook offers -110, decimal odds are 1.9091.
EV = 0.58 × 1.9091 − 1 = 0.106
That's +10.6% EV.
That's a value bet.
Expected value vs results
One of the most important lessons in sports betting is this:
A good bet can lose. A bad bet can win.
Expected value is about process, not one game.
That's why serious bettors track:
Expected value
Long term ROI
Closing line value
Performance by market and sportsbook
If you're not tracking results, you're making it much harder to know whether your edge is real. Use SlipSync to track every bet from every sportsbook. It tracks all your performance stats for you so you can know whether your EV lines up with your actual ROI.
Tools to make EV easier
You don't need to do every step by hand.
Useful tools mentioned earlier in this post include:
EV Calculator for fast expected value math
No Vig Calculator for fair probabilities
Odds Converter for converting American, decimal, and fractional odds
Kelly Calculator for stake sizing
SlipSync bet tracker to monitor results over time
FAQ
What is expected value in sports betting?
Expected value is the average amount you expect to win or lose on a bet over the long run based on your estimated win probability and the payout offered.
What is a positive EV bet?
A positive EV bet is a wager where your estimated probability of winning is high enough that the sportsbook’s odds are in your favor over time.
Is value betting the same as expected value?
They are closely related. Expected value is the math. Value betting is the act of placing bets when that math says the price holds positive expected value.
Can a negative EV bet still win?
Yes. Any single bet can win. Negative EV means the bet is unprofitable over a large sample, not guaranteed to lose tonight.
Why do bettors make negative EV bets?
Some do it because they prefer favorites, want bigger payouts, or value entertainment over profit. That's where ideas like prospect theory and utility theory come in.
Should I only bet positive EV bets?
If your goal is long term profit, yes. If your goal is entertainment, you may choose differently, but you should be honest about that tradeoff.
How do sportsbooks create negative expected value for bettors?
Sportsbooks build margin, or vig, into their prices. To find true value, bettors need to remove that margin, estimate fair probability, and compare it to the offered odds.
Bottom line
Expected value is the foundation of profitable sports betting. It tells you whether a bet is actually worth making based on probability and price.
Prospect theory explains why people often choose bad bets. Utility theory explains why some people knowingly choose fun over profit. But if your goal is to win long term, expected value should drive your decisions.
Start with fair probabilities. Compare prices across books. Calculate EV. Size intelligently. Track everything.
That's what value betting actually looks like.
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