How the numbers are made
Methodology
Every formula, every assumption, and the commercial arrangement behind the pages that carry links.
The conflict of interest, first
Links to sportsbooks on this site are commercial. When a reader opens an account through one, this site may be paid. That arrangement has one consequence worth stating before any arithmetic: the books listed here are the books we are able to link, which is not the same set as the books available to you. A sportsbook absent from these pages may well have the better offer, and its absence carries no information about its quality.
What the arrangement does not change is the ordering. The ranking on the sportsbooks page is produced by the conversion arithmetic below, applied identically to every entry. A commercial partner whose offer converts badly ranks badly, and the published method is what makes that checkable; nothing here rests on a promise.
Converting American odds
American odds are converted to decimal first, because decimal odds multiply and invert cleanly and every other calculation on the site depends on that. For a positive price A, the decimal is 1 + A/100. For a negative price, it is 1 + 100/|A|. The implied probability is 1/d, which is also the break-even win rate.
Intermediate values are never rounded. Only the display is, and a derived American price is rounded toward the book: positive prices down, negative prices away from zero. Three −110 legs multiply to a decimal of 6.957926, which is +595.79 exactly and posts as +595 rather than +596, because a book does not round a price in the bettor’s favour. Fair prices, which no book is posting, round to nearest instead.
Margin, hold and the difference between them
For a market with outcomes priced at decimals dᵢ, the book sum S is the total of 1/dᵢ. A fair market sums to 1. The overround is S − 1 as a percentage; the hold is 1 − 1/S. These are different numbers and the American industry uses the word “vig” for both, so both are printed and labelled wherever either appears. On a −110/−110 market the overround is 4.7619% and the hold is 4.5455%.
No-vig fair prices come from proportional normalisation: each implied probability is divided by S so the set sums to exactly 1. This is the standard method and it assumes margin is spread across outcomes in proportion to probability. Real books often load more of it onto longshots, so a fair price derived this way is slightly generous to favourites. On two-way markets near even the difference is negligible; on wide three-way markets it is not.
Parlays and bonus bets
A parlay decimal is the product of its legs. Its fair price needs the margin each leg’s market carries, which a ticket does not record, so that margin is an input defaulting to 4.7619%. Across n legs the offered price retains (1 + M)−n of the fair payout, so the book keeps the remainder. All of it assumes independent legs; same-game parlays are priced through a correlation model and this arithmetic does not describe them.
A bonus bet does not return its stake, so only the profit leg is paid. Its cash-equivalent value as a share of face is (1 − 1/d) / (1 + M). At even money and a standard margin that is 47.73%. Every welcome-offer figure on this site is that formula applied to the structure of the offer, and each structure is stated alongside the result so nothing is assumed.
Where figures come from, and where they do not
This site captures no odds. Nothing here samples sportsbook prices, maintains a register of them, or claims to have measured a market. Every number is either arithmetic on a price you enter, or a figure published in terms and dated where it appears.
Tax figures come from the IRS instructions for Forms W-2G and 5754 as revised in January 2026, and from the statutory change limiting deductible gambling losses to 90% from the 2026 tax year. State treatment varies and is not centralised here. None of it is tax advice.
Welcome-offer headlines carry the date they were checked and link to each operator’s own terms. They change frequently and differ by state, so the operator’s page is the authority and the dated figure here is a starting point. The offer structures, which drive the ranking, change far less often.
Every calculator is backed by a set of test vectors that are checked on every build, and the simulation on the bankroll page is validated against the closed-form result, never against itself. Where a figure cannot be derived honestly, the page says so instead of supplying one.
Questions about the method
5 questions
01 Why does the site print two margin figures instead of one?
Because they answer different questions and the industry uses one word for both. The overround is how far the posted prices sum past a fair book; the hold is the share of money staked the book expects to keep. On a standard two-way market at −110 those are 4.76% and 4.55%. They stay close at small margins and drift apart as margins grow, so a page that prints one under the other label is off by more the wider the market gets.
02 How is an American price converted?
To decimal first, because decimal odds multiply and invert cleanly and every later step depends on that. A positive price A becomes 1 + A/100; a negative price becomes 1 + 100/|A|. The implied probability is one divided by the decimal, which is also the break-even win rate for the bet.
03 Why do three −110 legs post at +595 rather than +596?
Because a derived American price is rounded toward the book instead of to the nearest whole number: positive prices down, negative prices away from zero. Three −110 legs multiply to a decimal of 6.957926, which is +595.79 exactly. A book would post +595, so that is what the calculator shows. Intermediate values are never rounded; only the display is.
04 What does the fair price on a parlay assume?
That the legs are independent and that each leg carries the market margin set in the assumptions box, 4.7619% by default, which is what a two-way market priced at −110 on both sides carries. A same-game parlay breaks the first assumption, because its legs describe one event and move together, so the arithmetic here does not describe it.
05 Where do the tax figures come from?
The federal treatment follows the rules the IRS publishes for the 2026 tax year, and the state rates are the 2026 individual income tax rates published by the Tax Foundation. Gambling winnings are ordinary income, so the rate that applies is the rate on a marginal dollar of income, and for a graduated state the figure shown is the top bracket. It is general information, not tax advice.