Period 2 · Odds & bonus maths
The margin a sportsbook charges is hidden in its odds: add up 1 ÷ decimal odds for every outcome in a market, and whatever exceeds 1 is the overround. At 1.91 on both sides of a two-way market the book keeps about 4.5% of every dollar staked in the long run; at 1.80 each way it keeps 10%. Provincial lottery sportsbooks and private books both price this way, but payout caps, rounding and void rules in the provincial game conditions can push your effective price lower than the odds on screen.
Every decimal price implies a probability: 1 ÷ odds. A fair market's implied probabilities add up to exactly 1 (100%). A bookmaker's add up to more, and that excess is the overround. From it you get the two numbers worth knowing:
Overround and margin are close but not the same: a 4.71% overround is a 4.5% margin. Use the margin when comparing books, because it is expressed per dollar you stake.
This works identically for OLG's PROLINE, which settles on decimal odds, for Loto-Québec's Mise-o-jeu, for PlayNow Sports in British Columbia and Manitoba, and for any private sportsbook. It does not require knowing who is "right" about the game; it only uses the prices the book publishes.
The odds below are illustrative, chosen to show the arithmetic. Pull real prices from the books you use and run the same sums.
| Market (example odds) | Implied probabilities | Sum | Overround | Margin |
|---|---|---|---|---|
| Two-way, 1.91 / 1.91 | 52.36% + 52.36% | 1.0471 | 4.71% | 4.5% |
| Two-way, 1.80 / 1.80 | 55.56% + 55.56% | 1.1111 | 11.1% | 10.0% |
| Three-way soccer, 2.40 / 3.30 / 3.00 | 41.67% + 30.30% + 33.33% | 1.0530 | 5.30% | about 5.0% |
Worked example, removing the margin: in the three-way market, divide each implied probability by 1.0530 to get the book's "fair" view: 39.6% home, 28.8% draw, 31.6% away. The fair odds are the reciprocals: about 2.53, 3.48 and 3.16. Compare those with the printed 2.40, 3.30 and 3.00 and you can see that the margin is taken off every outcome, not just the favourite.
The point for comparison shopping: if one book offers 1.91 each way and another 1.80 each way on the same game, the second costs you more than twice as much per dollar wagered over time, even though both show the same favourite.
Parlay odds are the product of the leg odds. The PROLINE game conditions say exactly this: multiply the odds for each correct selection to get the total odds, then multiply by the wager. Loto-Québec's Mise-o-jeu Rule 13 describes the same product of odds times the amount wagered. Because the odds multiply, so do the payout rates. A leg with a 95.5% payout rate becomes 95.5% × 95.5% on two legs, and so on.
| Legs | Payout rate at 4.5% margin per leg | Book's share | Payout rate at 9% margin per leg | Book's share |
|---|---|---|---|---|
| 1 | 95.5% | 4.5% | 91.0% | 9.0% |
| 2 | 91.2% | 8.8% | 82.8% | 17.2% |
| 3 | 87.1% | 12.9% | 75.4% | 24.6% |
| 4 | 83.2% | 16.8% | 68.6% | 31.4% |
| 5 | 79.4% | 20.6% | 62.4% | 37.6% |
| 6 | 75.9% | 24.1% | 56.8% | 43.2% |
The table is pure arithmetic (payout rate per leg raised to the number of legs) and assumes independent legs at the same margin. Two lessons follow. A modest gap in single-game margin turns into a large gap on a five- or six-leg ticket. And a parlay at a low-margin book can still cost more than a single at a high-margin book.
Odds are only half the price. The other half is in the rules on caps, rounding and voids. These are the published terms from three provincial products.
| Rule | OLG PROLINE (ON) | Loto-Québec Mise-o-jeu (QC) | PlayNow Sports (BC, MB) |
|---|---|---|---|
| Payout cap | $1,000,000 per ticket; slips that could exceed it are refused unless OLG elects otherwise | Loto-Québec may limit the prize to $2,000,000 per winning selection, shared pro rata among winners of the same selection | $200,000 per player for all bets settled in a calendar day; $50,000 on novelty bets |
| Stake limits | $1 minimum, $100 maximum (OLG may reduce the maximum); in-store limit of $100 per outcome per customer per day per location | Not stated on the rules page | Maximum bet may vary by player, sport, league or selection |
| Payout calculation | Product of decimal odds × wager, rounded to the nearest ten cents | Product of odds × wager, subject to dead-heat rule | Normal mathematical rounding to the cent |
| Voided leg in a parlay | Parlay recalculated with fewer selections, no refund | Predictions void if all participants tie | Per market rules |
| Dead heat | Payout reduced, but not below stake except head-to-head bets | Odds divided by number tied, not below 1.00 | Dead-heat reduction applied to the stake, not to the odds |
Sources: PROLINE Game Conditions; OLG sports wagering limits notice to retailers; Mise-o-jeu rules; PlayNow Sports Betting Game Conditions (August 28, 2023).
A cap matters only on big tickets, but when it bites it is brutal. Worked example at PlayNow: a $100 parlay with combined odds of 2,500 would return $250,000. Under the $200,000 daily maximum, the payout is $200,000, so the effective odds are 2,000. That is a 20% haircut on top of whatever margin was already built into each leg, and the PlayNow conditions say players waive any claim above the limit and are responsible for tracking it across all their bets.
At OLG the effect shows up earlier: a slip that could pay more than $1,000,000 is refused rather than trimmed. At Mise-o-jeu the cap is per winning selection and shared: if several people hit the same combination and the total exceeds the limit, each gets a pro-rata share. That last rule is unusual and worth knowing before playing a popular long-shot combination.
PROLINE's ten-cent rounding moves a payout by at most five cents, which is irrelevant at normal stakes. The void rule matters more. When a parlay leg is voided, PROLINE recalculates the ticket with the remaining legs. Your ticket survives, but at shorter odds, and the stake is not partly refunded.
Margin is a price; hold is what a book actually keeps after results. The two differ because bettors do not spread money evenly across outcomes and because results vary. For a benchmark, iGaming Ontario's 2024-25 annual report lists $11,414,317 thousand in betting wagers and $653,772 thousand in betting gaming revenue across the private regulated market. Dividing one by the other gives a realized hold of about 5.7% of stakes for that fiscal year, covering sports plus esports, proposition and novelty bets. The figure is an average over every type of bet, including heavy-margin parlays, so a disciplined single-game bettor at competitive prices should be paying less than that, and a habitual multi-leg bettor more.
In Ontario, the private books you are comparing against PROLINE+ should be ones registered with the AGCO and contracted with iGaming Ontario; our guide to checking a site's licence explains how. For how we weigh prices against other factors, see how we rate operators.
OLG's site terms set 18 as the minimum for in-store sports betting and 19 for online sports betting in Ontario. Loto-Québec's site states 18+. Online provincial products check that you are physically in the province when you bet.
None of this arithmetic makes betting profitable; it shows how much you are paying for the entertainment. A margin you can measure is a cost you can budget. If the budget keeps slipping, the responsible gambling page lists provincial limit tools and help lines.
Add 1 ÷ decimal odds for every outcome in the market, then take 1 minus 1 ÷ that sum. At 1.91 on both sides of a two-way market, the margin is about 4.5%.
It depends on the market; compare the same market's implied-probability sum at each book. Also check payout caps such as PROLINE's $1,000,000 per ticket.
Leg odds multiply, so the payout rates multiply too. Three legs at a 4.5% margin each leave the bettor about 87.1% of stakes in the long run.
Under OLG's game conditions the parlay is recalculated with the remaining selections and no amount is refunded.
Yes. PlayNow's game conditions set a $200,000 maximum payout per player for all bets settled in a calendar day, and $50,000 on novelty bets.
Prepared by the CasinoInspectors editors from the sources listed above. This is general information, not legal, tax or financial advice. Spotted a mistake? Write to [email protected]. Gambling help: ConnexOntario 1-866-531-2600.
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