Betting calculators
The same math Vault runs on every line: strip the hold to find the fair price, check whether a bet has positive expected value, size it, and see what a parlay or pick'em entry really needs to hit.
No-vig fair odds calculator
Enter both sides of a two-way market (over/under, spread, moneyline). The hold is the book's cut; removing it gives each side's fair probability and fair odds.
Expected value (EV) calculator
Compare your odds with the true chance of winning. Use the fair probability from the no-vig calculator above, or your own estimate.
Kelly criterion stake calculator
Kelly sizes a bet by how big your edge is. Full Kelly swings hard, so most bettors use a quarter or half. Vault's board uses quarter Kelly.
Parlay calculator
Combined odds and payout for up to 10 legs. Add each leg's fair win chance to see the parlay's real expected value, since the book's hold stacks on every leg.
Assumes legs are independent. Legs from the same game often move together (a QB over and his top receiver's over), which makes the true chance higher than this.
Pick'em break-even calculator (PrizePicks, Underdog, Sleeper)
Pick'em apps pay a flat multiplier, so there's no price on each pick. What matters is the win rate each pick needs for the entry to break even.
Power plays only. Flex entries pay on partial hits, which lowers the break-even; check your app's current payout table.
Odds converter
Type in any box to convert between American, decimal and implied probability.
Questions
What is the vig (hold)?
The book's built-in margin. At -110 on both sides each side implies 52.4%, adding to 104.8%. With money split evenly, the book keeps about 4.5% of everything bet: that is the hold. Scaling both sides back to 100% gives the fair 50/50.
What does positive EV mean?
Your odds pay more than the bet's true chance of winning is worth. A +5% EV bet returns $5 per $100 on average over many bets. Any single bet can still lose.
Why not bet full Kelly?
Full Kelly assumes your win chance is exactly right. It never is, and overestimating it with full Kelly can drain a bankroll fast. Fractional Kelly gives up a little growth for much smaller swings.
Where does Vault get fair probabilities?
Vault strips the hold from every book that prices both sides and takes the middle, or uses only sharp books like Pinnacle and the exchanges if you choose. See the public track record for how its grades have done.