What is Expected Value in Sports Betting?

Expected value (EV) is the mathematical average outcome of a bet if it were placed an infinite number of times under identical conditions. A bet with a positive expected value (+EV) will profit on average over time. A bet with a negative expected value (-EV) will lose on average over time. No matter how good the team looks or how confident you feel in the moment.

Here is the core idea: every sportsbook sets odds that imply a probability for each outcome. If the book prices the Toronto Maple Leafs at -130 on the moneyline, it is implying the Leafs have approximately a 56.5% chance of winning. If your own honest assessment, based on research, line movement analysis, or any other edge, puts the Leafs' true win probability at 62%, the gap between 62% and 56.5% represents your edge. A bet in this situation has positive expected value because you are consistently getting paid at odds that undervalue the true probability of winning.

This is exactly what our EV calculator measures. Enter the book's odds, enter your own probability estimate, and the calculator tells you the EV per dollar wagered, your edge over the book's implied probability, and, using the Kelly Criterion, the mathematically optimal stake size given your bankroll.

The EV Formula: Explained Step by Step

The expected value formula for a binary bet (win or lose) is straightforward:

Let's walk through a real Ontario example. FanDuel is offering the Ottawa Senators at +145 moneyline against the Toronto Maple Leafs. You analyse the game and conclude the Senators have a true 42% chance of winning, higher than the 40.8% implied by +145 odds.

The EV per $100 wagered is: (0.42 × $145) − (0.58 × $100) = $60.90 − $58.00 = +$2.90. Small? Yes. But place 500 similar-quality bets in a season and those edges compound. This is the foundation of every profitable sports betting operation in the world, from recreational Ontario bettors to quantitative hedge funds betting sports markets internationally.

Why Implied Probability is Not True Probability

The implied probability embedded in any sportsbook's odds already includes the book's margin (the vig). A standard -110/-110 two-sided market adds up to 104.5% implied probability. The extra 4.5% is the book's cut. This means the implied probabilities from any odds line are systematically overstated. A true 50/50 coin flip priced at -110 on both sides actually implies 52.4% on each side, an impossibility that only resolves in the book's favour.

Stripping the vig from a line to find the true implied probability is called finding the "no-vig" or "fair" line. Our Hold/Vig calculator does this automatically. For EV purposes, what matters is whether your estimated probability exceeds the implied probability including vig, because that is the price you are actually paying.

The Kelly Criterion: Sizing Your Bets for Maximum Growth

Identifying a +EV bet is half the battle. The other half is deciding how much to wager. Bet too little and you grow your bankroll too slowly. Bet too much, even on genuinely +EV opportunities, and variance can wipe you out before the edge has time to play out. The Kelly Criterion solves this problem mathematically.

Developed by Bell Labs scientist John L. Kelly Jr. in 1956 and applied to gambling by mathematician Edward Thorp, the Kelly formula calculates the exact fraction of your bankroll to wager in order to maximise the geometric growth rate of your bankroll over time while avoiding ruin.

Using our earlier Senators +145 example with a 42% true probability:

• Edge = 42% − 40.8% = 1.2 percentage points
• Full Kelly stake = ((1.45 × 0.42) − 1) ÷ (1.45 − 1) = (0.609 − 1) ÷ 0.45 = 0.87% of bankroll
• On a $10,000 bankroll: Full Kelly = $87 stake

Full Kelly vs. Fractional Kelly: What Professional Bettors Actually Use

Full Kelly is mathematically optimal if your probability estimate is perfectly accurate. In practice, probability estimates always carry uncertainty, and overestimating your edge even slightly causes Full Kelly to recommend stakes that are far too large for the true edge available. Professional sports bettors almost universally use Half Kelly (50% of the Kelly stake) or Quarter Kelly (25%) as a risk buffer.

EV Betting in Ontario's Regulated Market: What You Need to Know

Ontario's regulated sportsbook market, launched April 4, 2022 and managed by iGaming Ontario, is one of the most competitive legal betting markets in the world by number of licensed operators per capita. With more than 40 licensed sportsbooks competing for Ontario bettors, the market creates exceptional conditions for EV betting that do not exist in most other regulated jurisdictions.

Shopping Lines Across Ontario Books

The single highest-impact EV behaviour available to Ontario bettors is maintaining accounts at multiple licensed operators and comparing odds before placing every significant wager. A half-point difference on an NHL moneyline (say, -115 at one book versus -110 at another) reduces the vig you pay and improves your EV on every single bet, permanently. Over a full season of NHL betting, consistently getting the better side of half-point line differences is equivalent to finding dozens of additional +EV opportunities that bettors with only one account never access.

Pinnacle's Ontario operation is the benchmark for this exercise: its average margin across all markets (4.50% in independent testing, December 2025) is the lowest of any licensed Ontario operator. Every bet placed at Pinnacle is statistically better value than the same bet at a standard -110 book before any edge calculation is applied.

Which Ontario Books Are Best for EV Bettors?

The 5 Most Common EV Betting Mistakes (and How to Avoid Them)

EV and Kelly Betting: Frequently Asked Questions

How Parlay Math Actually Works

A parlay combines two or more independent selections into a single bet where every leg must win for the parlay to pay. The payout is calculated by multiplying the decimal odds of each leg together. A two-teamer at -110/-110 pays approximately +260 American odds, much higher than either individual bet, which is why parlays are so appealing.

The calculation itself is simple: convert each leg's American odds to decimal, multiply all legs together, convert back to American or apply to your stake. Our Parlay Builder does this instantly for up to 12 legs, showing combined odds, implied probability, exact payout, and per-leg breakdown.

The Compounding Vig Problem with Parlays

The fundamental mathematical problem with standard parlays is that the vig compounds across legs. Each leg in a parlay carries its own vig, and those margins multiply rather than add. The more legs you add, the worse the expected value.

Notice how the vig accelerates dramatically beyond 4 legs. A standard 5-team parlay at -110 per leg carries nearly 19% total vig. You are giving up nearly one dollar in five to the book before the game even starts. This is why the best advice for recreational bettors is to keep parlays to 2–3 legs maximum when the goal is value rather than entertainment.

Same-Game Parlays (SGPs): A Different Animal

Same-Game Parlays combine multiple selections from the same game rather than across different events. FanDuel, DraftKings, BetRivers, and most Ontario sportsbooks offer SGP builders. The mathematics differ fundamentally from standard parlays because the legs are correlated: player prop legs can co-vary with game outcome legs.

Books price SGPs with their own proprietary models that account for correlation. This means SGP odds are not simply multiplicative like standard parlay odds. Books adjust for the fact that, say, a Leafs moneyline win and an Auston Matthews over-0.5-goals bet are positively correlated events. The adjustment can go either way: positive correlation between legs may improve the odds relative to independent multiplication, while negative correlation worsens them.

When Parlays Actually Make Sense

Given the compounding vig problem, the question is not "should I ever bet parlays?" but "when does the entertainment and potential upside justify the mathematical cost?" Three situations where parlay value is defensible:

• Correlated legs across books: If you have identified that two outcomes in different games are more correlated than the market prices (for example, two quarterbacks who tend to both perform well in the same weather conditions), a parlay on both may have better EV than the vig suggests.
• Promotional parlay insurance: FanDuel's Parlay Insurance promotion (refund if one leg misses) improves parlay EV meaningfully by reducing the expected loss on near-misses. Factor promotions into your parlay math.
• Entertainment budget: If the $20 you are putting on a 5-team parlay is your entertainment budget for the night and you understand the expected outcome is losing $20 on average, that is a valid choice. The problem is treating long-shot parlays as serious investment strategy.

Parlay Betting FAQ: Canadian Edition

American Odds: The Standard Format in Ontario

American odds (also called moneyline odds) are the dominant format at every Ontario licensed sportsbook. They express the relationship between a $100 unit and the profit generated, with positive and negative signs indicating underdogs and favourites respectively.

Positive American odds (e.g. +150) show how much profit a $100 stake generates. +150 means a $100 wager wins $150 profit, for a total return of $250.

Negative American odds (e.g. -130) show how much you must stake to win $100 profit. -130 means you must wager $130 to win $100 profit, for a total return of $230.

Decimal Odds: The Most Intuitive Format

Decimal odds express the total return per unit staked, including the return of your original stake. They are the dominant format in Europe, Australia, and on international sportsbooks. Many Ontario bettors prefer decimal odds for mathematical calculations because of their simplicity.

To calculate profit: multiply your stake by (decimal odds minus 1). A $100 stake at 2.50 returns $250 total: $150 profit plus your $100 stake back. Implied probability is simply 1 divided by the decimal odds: 1 ÷ 2.50 = 40% implied probability.

Decimal odds below 2.0 correspond to favourites (negative American odds). Decimal odds above 2.0 correspond to underdogs (positive American odds). Exactly 2.0 is equivalent to +100 (even money).

Fractional Odds: The British Tradition

Fractional odds express profit relative to stake as a fraction. 11/10 means for every 10 units staked, you profit 11 units, equivalent to +110 American or 2.10 decimal. 1/2 means for every 2 units staked, you profit 1, making it a strong favourite equivalent to -200 American or 1.50 decimal.

Fractional odds are primarily encountered on UK-origin platforms and in horse racing coverage. Most Ontario sportsbooks default to American odds, though bet365 (a British operator) offers fractional display as a selectable option. For Canadian bettors, fractional odds are the least commonly encountered format in day-to-day wagering.

Implied Probability: The Universal Language Behind All Odds

Regardless of format, every set of odds expresses an implied probability of an outcome occurring. Understanding implied probability is more fundamental than mastering any specific odds format, because it allows you to compare the book's assessment of an event directly against your own.

Remember that implied probabilities from a book's odds line include the vig. The two sides of a standard -110/-110 market add up to 104.5%, not 100%. Use our Hold/Vig calculator to strip the vig and find the true no-vig implied probability for each side.

Which Odds Format Should Canadian Bettors Use?

Use the format that your primary Ontario sportsbook defaults to, which for the vast majority of platforms is American. For mathematical analysis (EV calculations, parlay building, vig measurement), decimal odds are the most computationally friendly because they feed directly into multiplication without conversion. Our EV calculator and Parlay Builder both support all three formats with live conversion.

For line shopping across Ontario's 40+ licensed books, developing fluency in American odds is non-negotiable. Decimal literacy is valuable for reading European soccer and international sports lines. Fractional odds proficiency is useful primarily for historical understanding and for navigating older British-heritage operators like bet365's UK-market content.

What is the Vig (Vigorish)?

The vig, also called juice, hold, or overround, is the commission embedded in a sportsbook's odds. It ensures the book profits regardless of the outcome of any given event by setting prices that, in aggregate, pay out less than they take in across all bets on both sides of a market.

The simplest illustration: a standard two-sided market at -110/-110. If the book takes $110 from bettors on Team A and $110 from bettors on Team B, it collects $220. It pays out $210 to the winning side (stake plus $100 profit). The $10 difference, 4.76% of the total handle, is the vig. The book profits $10 regardless of who wins.

For individual bettors, the vig manifests as a structural disadvantage: even if you had no skill or information advantage whatsoever, you would lose money at -110 odds because you need to win 52.4% of your bets just to break even. The vig is what you are paying for the privilege of having your bet accepted.

Vig Comparison: Ontario's Licensed Sportsbooks

One of the least discussed but most practically important differences between Ontario's 40-plus licensed sportsbooks is their vig structures. Books with lower average margins are objectively better for bettors, all else equal. Independent testing conducted in December 2025 across a sample of major markets produced the following estimates:

The Lifetime Impact of Vig on Your Betting Results

The vig's long-term impact is more significant than most recreational bettors appreciate, because it is a permanent, inescapable drag on every bet placed, not just on losing bets. Consider two Ontario bettors with identical skill levels placing 1,000 bets per year at an average stake of $100:

Over five years at those volumes, the vig differential alone is worth $7,500, entirely independent of skill. This is why professional bettors treat vig minimisation as a primary strategic objective, not an afterthought.

How Ontario Bettors Can Reduce the Vig They Pay

• Open a Pinnacle account: The single highest-impact action. At 4.50% average vig, Pinnacle has the lowest margin of any licensed Ontario sportsbook. Use it as your primary book for all game lines and totals.
• Shop lines across Ontario books: Even half-point differences in spread prices translate to meaningfully lower effective vig. A market at -108 versus -113 for the same outcome carries approximately 1.5% less vig. Accounts at 3–5 Ontario books enable systematic line shopping.
• Avoid high-leg parlays: As demonstrated above, vig compounds aggressively beyond 3 legs. The 19%+ vig on a 5-team parlay is functionally a casino edge-level disadvantage.
• Use the Vig Calculator before betting: Make it a habit to run the two sides of any market you are considering through the Hold/Vig calculator before placing your bet. If the vig exceeds 7%, consider whether a better-priced equivalent exists at another Ontario book.
• Focus on the highest-liquidity markets: Books compete most aggressively on widely-bet markets like NFL spreads, NHL moneylines, and NBA totals, where their vig is lowest. Niche and secondary markets carry systematically higher margins.

How Sports Arbitrage Works: A Real Ontario Example

An arbitrage opportunity arises when two or more sportsbooks offer sufficiently different odds on both sides of the same market that backing both sides with optimally calculated stakes guarantees a profit regardless of outcome. The mathematical condition for a true arb is that the sum of the implied probabilities across all outcomes is less than 100%.

In practice: Pinnacle offers the Winnipeg Jets at +115 on a Monday morning. FanDuel has the opponent, the Minnesota Wild, at +110. The implied probability of Jets +115 is 46.5%. The implied probability of Wild +110 is 47.6%. Combined: 94.1%, well below 100%, meaning a guaranteed profit exists by betting both sides with the correct stake split.

Our Arbitrage Finder calculates this stake split instantly: enter the odds from both books, set your total bankroll allocation, and it shows you the exact stakes to place on each side and the guaranteed profit. No spreadsheets required.

Finding Arb Opportunities in Ontario's Regulated Market

With 40-plus licensed Ontario sportsbooks posting odds on the same events, pricing discrepancies occur continuously throughout every major sporting day. The challenge is finding them quickly, before the slower books adjust to match the market price. Typical arb windows in Ontario's competitive market last minutes to hours depending on the sport and market.

High-probability sources of Ontario arb opportunities include:

• Pinnacle vs. recreational books: Pinnacle accepts sharp action and adjusts its lines quickly. Many recreational books (FanDuel, DraftKings, theScore) lag Pinnacle's line moves by 15–60 minutes, creating windows where Pinnacle's updated price combined with a recreational book's stale price produces an arb.
• Opening line disparities: When books post their first lines on games 5–7 days ahead, significant pricing differences are common. These are typically the widest arb windows available before markets tighten as the event approaches.
• Player prop markets: Prop lines vary more widely between books than game lines because they are lower-volume and less efficiently priced. BetRivers' Prop Central and FanDuel's prop market are worth monitoring simultaneously for the same player stat lines.

The Real Risks of Arbitrage Betting in Ontario

Arbitrage appears risk-free in theory, and mathematically it is, if executed perfectly. In practice, several risks require management:

Best Ontario Sportsbooks for Arbitrage Bettors

The ideal arb portfolio in Ontario combines one sharp, limit-friendly book with several recreational books to access the widest possible line discrepancies. The optimal combination:

• Pinnacle (primary sharp leg): Never limits winning accounts, posts sharp lines early, accepts high stakes. The cornerstone of any serious Ontario arb portfolio.
• bet365 (deep markets + live arbs): Deep international coverage creates arb opportunities against North American-focused books. Live betting interface is fast enough for live arb execution.
• FanDuel + DraftKings (recreational legs): Both post slightly lagged lines relative to Pinnacle and bet365 on North American sports, creating regular windows. Both have higher vig that makes them less ideal for standalone betting but useful as arb counterparts to sharper books.
• BetRivers (prop arbs): Prop Central's deep prop market creates arb opportunities against books with narrower prop offerings. Combine with FanDuel's prop market for maximum prop arb coverage.

Arbitrage Betting FAQ