The Most Important Number in Betting

Expected value (EV) is the single most important number in all of sports betting. It's not just a formula, it’s your compass. Whether you’re a data-driven bettor or someone placing occasional wagers, EV tells you whether a bet is worth making over the long haul. Instead of focusing on wins and losses, sharp bettors focus on value, measured through this key equation.

What Is Expected Value (EV) and Why It Matters

EV calculates the average result you’d expect if the same bet were placed repeatedly under identical conditions. It helps you understand whether your wager is profitable in the long term—not just this time.

The Formula:

EV = (Probability of Win × Profit) + (Probability of Loss × Loss)

Example:

• Bet: $100 on Chicago Sky at +200

• Implied probability: 33.33%

• Your projected probability: 45%

• Profit if correct: $200

• Loss if incorrect: $100

EV = (0.45 × 200) + (0.55 × -100) = 90 - 55 = +$35

That positive number means you’d expect to win $35 per wager over a large sample if your estimated probability holds true.

Jamie vs. Leo: A Tale of Two Bettors

Meet Jamie, a basketball bettor who built a reliable model that evaluates player usage, injury trends, and efficiency margins. In April, her system flagged 80 bets with a projected edge of 3% or more.

• Average bet: $100

• Expected gain per bet: $6

• Projected monthly profit: $480

• Actual profit: $420

  
  

Jamie also tracks closing line value (CLV). She beat the closing number in 70% of her wagers, suggesting her reads are sharper than the market’s consensus.

Now contrast that with Leo, a high-action bettor who also places $100 wagers, but based mostly on hunches and public trends. He ends the month down $260 and can’t say whether he had an edge on any individual play. Leo doesn’t track outcomes or compare his lines to closing odds, leaving him blind to whether his bets are good or just lucky.

The difference isn’t just performance. It’s process.

Quantifying Your Edge and ROI

To measure edge:

Edge = Your Probability − Implied Probability

If you believe the Indiana Fever have a 56% chance to win, and the book’s line implies 52.38%, you’ve found a 3.62% edge.

To measure ROI:

ROI = (Profit / Total Wagered) × 100

For example, if Jamie wagers $5,000 and profits $300, her ROI is 6%—a strong return, especially over volume.

EV in Parlays: Rare but Real Opportunities

Parlays can be lucrative but deceptive. Each added leg introduces compounding vig, which means most parlays carry negative expected value. But if every leg in a parlay is individually +EV and uncorrelated, the combined ticket can be profitable.

Example:

• Leg 1: Aces moneyline at +110 (true line: +100)

• Leg 2: Over 159.5 at -110 (fair odds: -105)

This parlay has a sliver of edge, but success hinges on accurate joint probability modeling—a complex task even for seasoned bettors. Most should stick to single bets unless every leg has been carefully vetted.

Why Variance Doesn’t Equal Failure

Variance is not the enemy of good betting, it’s the turbulence on the way to your destination. Imagine you’re flying from LA to New York. You may hit some bumps, but the plane is still headed east. That’s how EV works.

A 6–14 record in your first 20 +EV bets doesn’t mean your model is broken. It means you’re facing randomness in a small sample. Over 500 bets, your edge emerges clearly.

Professional bettors accept that results lag process. They track bets, evaluate CLV, and stay disciplined through swings.

How Experts Use EV Strategically

Elite bettors don’t guess, they model. Here’s how they build their edge:

• Efficiency stats: Offensive rating, pace, effective FG%

• Travel and rest factors: Back-to-backs, cross-country trips

• Injuries: Depth chart impact, substitution quality

• Public perception: Fading hype and recency bias

• Line movement: Identifying early vs. late market sentiment

They remove the vig from odds to estimate true probability, compare it to their projections, and look for edges. If they find one, they line shop across books to improve payout, even a 5-cent difference can compound over time.

The Kelly Criterion: Smarter Staking, Not Bigger Bets

The Kelly Criterion is a formula used to determine optimal bet size based on your edge and the odds.

Formula: Bet Size (%) = Edge / (Odds − 1)

If your edge is 5% and the decimal odds are 2.0, you’d bet 5% of your bankroll. But this assumes your probabilities are rock solid. Many sharp bettors use half-Kelly or flat betting to minimize risk of ruin while still benefiting from compounding growth.

EV and CLV: Your Twin Scorecards

These two metrics answer different questions:

• EV tells you whether a bet is mathematically sound.

• CLV tells you whether you beat the market.

A bettor who consistently closes better than the final number is likely betting with insight, even if short-term losses occur.

Avoiding Common Mistakes with EV

Even bettors who understand EV make errors, like:

• Overestimating their edge based on faulty logic or limited data

• Ignoring sample size, misjudging short-term results

• Changing unit size impulsively

• Chasing action, even without value

• Failing to track bets, undermining future analysis

Three Takeaways to Bet Like a Pro

1. Strip out the vig to see fair odds and implied probabilities.

2. Only bet when your projection beats the market price.

3. Track outcomes and CLV to refine your edge over time.

   
   

Conclusion: EV Is Your Edge, Use It

Jamie’s success isn’t about being lucky. It’s about trusting the math. She doesn’t need a perfect month, she needs a repeatable edge. So do you.

If you want to bet with confidence, calculate your probabilities, compare them to the market, and only strike when value exists. Keep track, stay patient, and let the numbers guide you.

Because in the end, sports betting isn’t just a guessing game. It’s a math game—and math, played right, wins.