Definition
Chalk in betting means the favorite, especially a heavy favorite with short odds. Betting the chalk means backing the side the market prices as more likely to win.
For American odds, negative odds show how much you must risk to win $100. The implied probability formula for negative odds is:
odds / (odds + 100)
Use the absolute value of the negative odds. A -200 favorite has an implied probability of:
200 / (200 + 100) = 66.67%
Worked Example
A basketball team is priced at -250 on the moneyline. That team is the chalk.
A $250 bet at -250 wins $100 in profit if the team wins, for a total return of $350 including stake.
The implied probability is:
250 / (250 + 100) = 71.43%
If your own projection gives that team a 75% chance to win, the bet has a positive expected-value case before considering limits, timing, and market movement.
Why It Matters
Chalk helps a bettor identify when the market has made a team expensive to back. The key question is not whether the favorite is likely to win, but whether the price is still better than the bettor’s projected probability.