Odds calculators
15 free calculators. No account needed.
15 free calculators for converting promos, reading prediction markets and shopping lines. Pick one, type in a box, and the answer is already there. No account needed.
Prediction market price to American odds
Kalshi and Polymarket quote a contract as a price. A sportsbook quotes the same thing as a line. Type either one and you get the other. Paste the price however you have it: 63, 63%, 63c and $0.63 all read the same.
Kalshi's published taker fee: 7% × contracts × price × (1 − price), rounded up to the cent, on a 100 contract order. Most Polymarket markets charge no fee.
A 63.0¢ Yes contract is the same bet as -170 at a sportsbook, and the No side is +170.
This is the raw conversion with no margin in it. A sportsbook adds its margin on top, so the line a book posts on the same event is usually worse than this number. When a book beats it, you have found something.
Odds format converter
American, decimal, fractional and implied probability are four ways of writing the same price. Change any box and the other three follow.
Open with the full explanation →Fractional odds come off a fixed ladder of denominators, so the fraction shown is the closest one a board would print rather than an exact ratio with a four digit denominator.
No vig odds and hold
A book prices both sides so the chances add up to more than 100%. The extra is its margin. Put both sides in and this takes the margin out, leaving what the book really thinks the chances are.
Open with the full explanation →The margin is split in proportion across the sides, the standard method and the right one for two way markets. On a long futures board with a heavy longshot it is not, so do not read this as a fair price on a 20 runner field.
Bonus bet conversion calculator
A bonus bet is not cash. If it wins, the book keeps the stake and pays only the winnings, so a $200 bonus bet is worth well under $200. This works out the bet on the other side that leaves you the same money either way.
The book's money. If it wins you keep the winnings, not the stake.
Real prices move while you place, and an exchange takes a fee on the cover leg, so your number lands close to this rather than exactly on it.
The math is the easy half. Finding a cover price that leaves you this much, at a book you can still bet at, in your state, is the part Promonyx does for you.
Try it on a real promoProfit boost calculator
A profit boost raises the winnings on one bet. Place the boosted bet with your own money, hedge the other side, and the extra winnings become profit you keep either way.
Conversion here is what you keep as a share of the stake times the boost, the same measure Promonyx uses for every boost. Some books cap the extra winnings a boost can pay; if yours does, keep the stake low enough that the extra stays under the cap.
Second chance (sweat free) bet calculator
Bet with your own money. If it loses, the book refunds you in bonus bets. Because the refund only comes when you lose, the hedge is smaller than a normal one, and the refund does part of the covering.
This assumes the refund arrives as bonus bets. If your book refunds in cash, set the rate to 100%. Once the refund lands, convert it with the .
Bet & Get (qualifying bet) calculator
Place a qualifying bet with your own money and the book gives you bonus bets whatever happens. Hedge the qualifying bet close to even so it costs you little, and the bonus is the profit.
This assumes the bonus lands whatever the qualifying bet does. Some promos only pay it if the bet wins or only if it loses; a refund only on a loss is the . Convert the bonus itself with the .
Deposit match calculator
The book matches part of your deposit. What that is really worth depends on how it pays out: as bonus bets you convert, or as site credit that unlocks as you wager.
It stays worth doing as long as each $1 wagered costs you under 35.0%.
Most books make you bet the deposit once before the bonus lands, so that is counted as the wagering here. Hedge it close to even and it costs little.
Hedge calculator
You have a live bet and want the same money whichever way it lands. This sizes the other side. Both legs here are your own cash. If the first leg is a bonus bet, use the instead, because a bonus bet does not give the stake back.
Open with the full explanation →Arbitrage calculator
When two books disagree enough, you can back both sides and win either way. Put the best price on each side in, plus what you want at risk in total, and this splits it.
Open with the full explanation →Prices move while you place the second leg, and books limit accounts that do this often. Treat the number as the best case, not the expected case.
Middle calculator
The line moved, and now one book has Over 44.5 while another has Under 47.5. Take both and you lose a little most of the time, but if the result lands in the gap, both bets win.
How often a gap lands depends on the sport and the numbers. A three point gap around 45 in the NFL crosses key numbers and lands far more often than the same gap in basketball. This calculator tells you the rate you need, not the rate you will get.
Expected value calculator
What a bet is worth on average, given what you think the real chance is. A prediction market price is a good source for that chance.
Closing line value calculator
The closing line is the sharpest price a game ever gets. Beat it regularly and you are beating the market, whatever the results say this week. Put in the price you took and where the line closed.
Kelly stake calculator
How much to put on a bet you think is priced wrong. A bigger edge means a bigger bet, and Kelly is the math that says how much bigger.
Full Kelly assumes your chance estimate is exactly right. It almost never is, and being a little wrong at full Kelly is how people go broke while still picking winners. Quarter is the setting most people should stay on.
Parlay odds calculator
Multiply legs into one price. Fill in as many as you have and leave the rest blank.
This treats every leg as independent. Legs from the same game are not, and a book prices a same game parlay on its own model, so that ticket will not match this number.
About these calculators
Why a prediction market price is worth converting
Kalshi and Polymarket run as exchanges. People trade against each other and the price settles where the money balances, so the number on the screen is close to what the market really thinks. A sportsbook adds its own margin on top of its number, which is why both sides of a coin flip pay -110 instead of +100.
Convert the exchange price and you have a fair line to hold the book against. When the book is better than the fair line, you are getting the good side of the bet. When it is worse, the difference is the book's margin and you are paying it.
Worth saying plainly: none of these calculators finds you a price. They do the math on prices you already have. Finding the price is the part Promonyx does.
4 of these have a page of their own
The same calculators, with the explanation that goes with each one: what the numbers mean, when the tool is the right one to reach for, and what usually goes wrong.
Where the conversion targets come from
The promo calculators grade your result against the same targets the Promonyx app uses: 70% for a bonus bet, 60% for a profit boost, and 45% for a second chance bet. Gold means you hit it. Anything under it still makes money, just less than a good conversion should.