Calculators
Ten free tools that teach, calculate and interpret. Every result depends on the numbers you enter, so each one explains how to read it. Nothing here is a pick, and no outcome is guaranteed.
Price & probability
Turn a price into a probability, strip out the margin, and compare books.
Implied Probability Calculator
Convert American odds into the break-even probability the price demands.
How to read it: at this price you must win more often than the break-even percentage just to come out even. Your estimate is an assumption, not a fact, and a positive result here does not mean a bet will win. Educational use only.
Companion guide: Odds & Implied Probability Cheat Sheet (PDF · 2 pages)
No-Vig Fair Odds Calculator
Remove the sportsbook margin from a two-way market to see the fair price it implies.
How to read it: the two implied probabilities add up to more than 100% — the extra is the overround (margin). Hold is that same cut expressed as a share of the total, so it is always a little smaller. Scaling both back to 100% gives the no-vig estimate of what the market thinks. It is an estimate of the market, not a prediction of the game. Educational use only.
Companion guide: Fair Odds & No-Vig Prices (PDF · 3 pages)
Odds Converter
Convert between American, decimal and fractional odds and implied probability.
How to read it: all four are the same price in different clothes. Implied probability is the win rate the price needs to break even — it includes the sportsbook margin. American odds from decimal are rounded to the nearest whole number. Educational use only.
Companion guide: Odds & Implied Probability Cheat Sheet (PDF · 2 pages)
Hold & Line Shopping Calculator
Enter both sides of the same market at each book. See the margin each carries and where the best price is.
| Book | Side A odds | Side B odds | Margin | Hold |
|---|---|---|---|---|
| – | – | |||
| – | – | |||
| – | – | |||
| – | – |
How to read it: margin = both implied probabilities added, minus 100%. Hold = the share of the total the book keeps, 1 − 1 ÷ (sum of implied probabilities). At -110/-110 the margin is 4.76% and the hold is 4.55%. Leave a row blank to skip it. Check that every row is the same line and market. Sample books are fictional. Educational use only.
Companion guide: Line Shopping & Closing-Line Value (PDF · 3 pages)
Value & staking
What a wager is worth if your estimate is right, and how much to risk. Both depend on your own estimate.
Expected Value Calculator
See what a wager is worth on average if your win probability is right.
How to read it: EV = (win probability × profit) − (loss probability × stake). It is an average over many wagers if your probability is right — never a prediction for one wager, and your probability is an assumption. Educational use only; no outcome is guaranteed.
Companion guide: Expected Value Explained (PDF · 3 pages)
Fractional Kelly Stake Guide
A cautious stake-size guide with an uncertainty haircut and hard caps. Education only.
How to read it: Kelly = (b·p − q) ÷ b, where b is the net decimal odds, p your win probability and q = 1 − p. It assumes your probability is exactly right, which it never is, so we trim it, use only a fraction and let a hard cap override the result. Never use money you need, and never chase a loss. Educational only, not financial advice.
Companion guide: Units, Bankroll & Fractional Kelly (PDF · 3 pages)
Parlay Calculator
See what a parlay pays, the win rate it needs, and how the margin compounds.
| Leg | American odds | Your win % (optional) |
|---|---|---|
| 1 | ||
| 2 | ||
| 3 | ||
| 4 |
How to read it: a parlay multiplies the legs’ decimal odds, and so it multiplies the sportsbook margin too. Add your own win % for every leg to see an EV estimate; it assumes the legs are independent, which is often false — correlated legs change the math, usually against you. Educational use only; no outcome is guaranteed.
Bankroll & Unit Planner
Turn a bankroll into a unit size, stake tiers and a weekly risk limit. Education only.
| Tier | Units | In dollars |
|---|
How to read it: a unit is normally about 1% of the active bankroll. Stakes stay fixed in units — a loss never raises the next one. Streaks of 5 or more losses in a row are normal even for a good process, so plan for them. Never use money needed for rent, bills or savings. Educational guidance, not financial advice; your own limits always come first.
Companion guide: Units, Bankroll & Fractional Kelly (PDF · 3 pages)
Lines & timing
What a half point is worth, and whether the price you took beat the close.
Half-Point & Alternate Line Calculator
Compare a whole-number line with a half-point line using your own assumptions.
How to read it: on the whole-number line a game that lands on the key number is a push (stake back). The half-point line has no push. Both c and k are your own beliefs — we do not supply key-number frequencies, because they vary by sport, era and rules. If you cannot back them with data you trust, take the better price or pass. Educational use only.
Companion guide: Half-Points & Key Numbers (PDF · 3 pages)
Closing-Line Value (CLV) Calculator
Compare the price you took with the closing price, bet by bet.
| # | Price you took | Closing price | CLV |
|---|---|---|---|
| 1 | – | ||
| 2 | – | ||
| 3 | – | ||
| 4 | – | ||
| 5 | – | ||
| 6 | – |
How to read it: CLV (points) = implied probability of the closing price − implied probability of the price you took. Positive means you got a better price than the market’s final one. It is a process score, not proof of profit; a small sample is noisy, and positive CLV never guarantees a result. Educational use only.
Companion guide: Line Shopping & Closing-Line Value (PDF · 3 pages)
Educational use only. Results are arithmetic on the numbers you enter, not predictions, and any wager can lose. Adults 21+ only. Responsible betting · All resources