Sports Betting Fundamentals

Odds Formats: Decimal, Fractional, American

Decimal 2.40, fractional 7/5, and American +140 all price the same bet: a $50 stake returning $120. Learn what each format says and how to convert in seconds.

Implied Probability in Betting Odds

Divide 1 by the decimal odds and any betting line becomes a percentage: 2.50 implies 40%, the standard -110 implies 52.4%. The one formula behind every price.

The Vig: The Bookmaker's Margin

The vig is the bookmaker's built-in fee: both sides of a standard -110 line sum to 104.8%, a 4.8-point overround worth about 4.5% of everything wagered.

Moneyline, Spread, and Totals

Moneyline, spread, and totals are the three core bets on any game. One matchup, worked in real numbers: Dallas -280 implies 73.7%, -6.5 must cover, 44.5 total.

Parlays and Props

Parlays multiply payouts and the bookmaker's edge together: three -110 legs surrender about 13% of fair value versus roughly 4.5% on one straight bet.

Live Betting: Why In-Play Odds Cost More

In-play odds reprice by the second and cost more: a 102.4% pre-game overround can run 109.1% live, nearly four times the margin, right when discipline is weakest.

Value Betting: Finding Positive EV Odds

A value bet is one where your probability estimate beats the line's: back a 45% chance priced at +150 (40% implied) and you earn about 12.5 cents per dollar.

Line Shopping and Staking

Shop the same bet across books and stake a flat 1-2% unit: taking -105 over -110 swings the ledger by about $225 per 100 bets on the exact same picks.