Calculator

Prediction Market Odds Converter

About this calculator

By Alex Thornton · author of the MIT-licensed teachersbettextbook library · Last reviewed 24 July 2026

Every converter turns 65 cents into −186 and stops. As a taker, you are paying −199.

Comparing a contract against a sportsbook price? The prediction market arbitrage calculator nets the fee out of both legs →

A prediction market odds converter turns a contract price into the formats bettors read: implied probability, decimal, fractional and American. Then it adds the exchange fee to show what the position really costs.

Two numbers, not one

A contract price is already a probability. 65 cents means the market thinks 65%, and it takes no conversion at all to see that.

But the fee is charged on top of the price, so what you actually have to clear is higher than what the price says. Those are two different numbers, and most tools print only the first one.

The gap looks tiny in cents and enormous in American odds. That is the whole reason this page exists.

Want more math?the Nerd Corner

P \;\longrightarrow\; \underbrace{q = P}_{\text{implied}},\quad \underbrace{d = \tfrac{1}{P}}_{\text{decimal}},\quad \underbrace{b = \tfrac{1-P}{P}}_{\text{fractional / net}},\quad \underbrace{P^{*} = P + 0.07\,P(1-P)}_{\text{fee-adjusted}}

where:

$P$ : the contract price in dollars, between 0 and 1. Kalshi quotes whole cents, so 65¢ is $P = 0.65$ .
$q$ : the implied probability, dimensionless. On a two-sided exchange quote it equals $P$ exactly.
$d$ : decimal odds, total return per $1 risked, stake included.
$b$ : net decimal odds, profit per dollar risked, and the fractional quote reduced ( $b = 7/13$ prints 7/13).
$A$ : American odds, $A = +100\,b$ when $b \geq 1$ (that is, $P \leq 0.50$ ), otherwise $A = -100/b$ .
$P^{*}$ : the fee-adjusted break-even probability, the all-in cost per $1 of payout on the standard Kalshi taker schedule. The effective price.
$C$ : number of contracts. The fee applies to the order total, rounded up to the next cent.

Worked example: the numbers in the form below

100 contracts at 65¢, taken from the ask (taker):

q = 65.00\%, \qquad d = \tfrac{1}{0.65} = 1.5385, \qquad b = \tfrac{0.35}{0.65} = \tfrac{7}{13}, \qquad A = -\tfrac{100 \times 0.65}{0.35} = -185.71

\text{fee} = \lceil\, 0.07 \times 100 \times 0.65 \times 0.35 \,\rceil_{\text{cent}} = \lceil \$1.5925 \rceil = \$1.60

\text{all-in} = \$65.00 + \$1.60 = \$66.60 \;\Longrightarrow\; P^{*} = 66.60\%

d^{*} = \tfrac{1}{0.665925} = 1.5017, \qquad A^{*} = -\tfrac{100 \times 0.665925}{0.334075} = -199.33

The screen says −186. The till says −199, 13.6 points apart. The closed form (66.5925%) sits just under 66.60% because the fee rounds up to a whole cent.

Compute the fee side on your own price

The conversions are fixed arithmetic on $P$ ; the fee moves with order size, so this panel computes it live.

Why the price is already the probability

A binary contract has two payoffs: $1.00 if the outcome happens, $0.00 if it does not. A risk-neutral buyer pays the expected payoff:

\mathbb{E}[\text{payoff}] = p \times \$1.00 + (1-p) \times \$0.00 = p

so price and probability are the same number in different units. YES at 65¢ and NO at 35¢ sum to $1.00 by construction: nothing to de-vig, and de-vigging anyway only adds error. A sportsbook’s two prices sum past 100% instead, so comparing them means adding the fee to one side and removing the vig from the other.

Reference table: contract price in every format

Fee columns use the standard Kalshi taker rate, $0.07\,P(1-P)$ , before the cent rounding. Rates are the exchange’s published schedule and can vary by market.

Price	Implied	Decimal	Fractional	American	Taker fee	Fee-adj. break-even	Fee-adj. American
5¢	5.00%	20.0000	19/1	+1900	0.333¢	5.3325%	+1775
10¢	10.00%	10.0000	9/1	+900	0.630¢	10.6300%	+841
25¢	25.00%	4.0000	3/1	+300	1.313¢	26.3125%	+280
50¢	50.00%	2.0000	1/1	+100	1.750¢	51.7500%	−107
65¢	65.00%	1.5385	7/13	−186	1.593¢	66.5925%	−199
90¢	90.00%	1.1111	1/9	−900	0.630¢	90.6300%	−967
95¢	95.00%	1.0526	1/19	−1900	0.333¢	95.3325%	−2042

Cheap in cents, expensive in percent

The fee peaks at a coin flip and shrinks toward the tails. Divide it by the outlay and the price cancels:

\dfrac{0.07\,P(1-P)}{P} = 0.07\,(1-P)

The fee eats 6.65% of every dollar at 5¢ and 0.35% at 95¢. The cheapest contracts carry the heaviest proportional cost: the inverse of sportsbook vig, which is heaviest on longshots in cents and percent.

Fair probability and break-even are two different numbers

$P^{*}$ is arithmetic on a posted price: what the contract costs, all in, per $1 of payout. Your fair probability $p$ is an estimate of how often the event happens. Expected value is the gap:

\mathrm{EV}_{\text{per contract}} = p \times \$1.00 - \bigl(P + 0.07\,P(1-P)\bigr) = p - P^{*}

When your own estimate lands exactly on the fee-adjusted break-even (66.60% on the worked example), expected value is $0, and it prints as $0, not “marginal value” and not a rounding opportunity. A tool printing one number labelled “fair odds” has merged $p$ and $P^{*}$ , and the edge is then unrecoverable.

Maker, taker, and the flat 0.25% case

\text{taker} = \lceil\, 0.07\,C\,P(1-P) \,\rceil_{\text{cent}} \qquad \text{maker} = \lceil\, 0.0175\,C\,P(1-P) \,\rceil_{\text{cent}}

A resting order pays about a quarter of what crossing the spread costs, at the risk of never being filled. Settlement is free, so a round trip pays the fee twice and holding to resolution pays it once.

Some major events replace the maker formula with a flat 0.25% of notional: 0.25¢ per contract at any price. Setting the two maker schedules equal,

0.0175\,P(1-P) = 0.0025 \;\Longrightarrow\; P(1-P) = \tfrac{1}{7} \;\Longrightarrow\; P = \tfrac{1 \pm \sqrt{3/7}}{2}

gives crossover prices of 17.27¢ and 82.73¢: inside them the flat schedule is cheaper, outside them worse. Below 3.71¢ a flat-schedule maker pays more than a standard-schedule taker: the discount inverts. Which schedule applies is stated on the contract.

The fee is rounded up to the next cent on the order total, so one contract at 50¢ pays $0.02 against a stated $0.0175, a 14.3% surcharge, gone by 100 contracts.

Buying NO at $1-P$ and selling YES at $P$ are the same position at the same fee, so the converter runs from either end. Which side you actually pay is set by the book: on a 64¢ bid / 65¢ ask, a taker buys YES at 65¢ and NO at 36¢.

What the converted number is not

It is not a prediction, and the exchange is not an oracle. A 2026 study of 300,000+ settled Kalshi contracts found prices informative, and low-priced contracts still winning less often than the fee-adjusted break-even required.^[2] That is the favorite–longshot bias, measured at racetracks in 1949^[3] and in nearly every betting pool since; this site shades tail prices rather than taking them at face value.

Two more things the conversion cannot see. Staleness: a quote nobody has touched in three hours converts as cleanly as a live one, which is why every number here carries a compute time and a venue-update time. Depth: the ask prices only the contracts resting at it: if 40 sit there, a 500-contract order fills worse.

Check this number yourself

The fee math is four public functions in the MIT-licensed teachersbettextbook package: same formulas, same rounding rule.

pip install teachersbettextbook

>>> from teachersbettextbook import kalshi_fee, kalshi_breakeven, kalshi_fee_of_outlay
>>> kalshi_fee(100, 0.65)          # 100 contracts at 65 cents, taker
1.6
>>> kalshi_breakeven(0.65)         # closed form, before the cent rounding
0.665925
>>> kalshi_fee_of_outlay(0.05)     # the fee as a share of money at risk
0.0665

The conversions are one line each: 1/P, (1-P)/P, and the sign rule above. More: open source.

Sources

Kalshi. “Fee Schedule” (July 2026 revision). Taker and maker formulas, the round-up rule, the flat 0.25% variant, and the zero settlement fee.
Burgi, C., Deng, W. & Whelan, K. (2026). “Makers and Takers: The Economics of the Kalshi Prediction Market.” GWU Working Paper 2026-001. PDF. 300k+ settled contracts: informative prices, favorite–longshot bias after fees.
Griffith, R. M. (1949). “Odds Adjustments by American Horse-Race Bettors.” American Journal of Psychology 62(2), 290–294.

Frequently asked questions

How do you convert a prediction market contract price to odds?

A contract price in dollars is already the implied probability. Decimal odds are 1 divided by P, net fractional odds are (1−P)/P reduced, and American odds are +100(1−P)/P at or below 50¢ and −100P/(1−P) above it. A 65¢ contract is 65% implied, 1.5385 decimal, 7/13 fractional and −186 American.

What is the fee-adjusted price of a prediction market contract?

The contract price plus the per-contract trading fee, expressed back in odds. On the standard Kalshi taker schedule that fee is 0.07 × P × (1−P), so a 65¢ contract costs 66.59¢ for a claim that pays $1.00: 1.5017 decimal, or −199 American against the −186 the screen shows.

Is the contract price the same as the fair probability?

No. The price converts to a break-even probability, which is arithmetic on a posted number. The fair probability is a separate estimate of how often the event happens. Expected value is the gap between the two, so a tool printing only one of them cannot show an edge.