Kalshi Fair Odds Calculator

How to Use the Calculator

1. Grab both sides from Pinnacle or PS3838. You want a two-way market: moneyline, yes/no, or any binary pair. Pinnacle posts both sides at the same time with tight spreads.
2. Pick your odds format. Decimal (1.91), American (-110), or Fractional (10/11) all work. The tool converts internally.
3. Choose a devig method. Start with Proportional for 50/50 markets. Switch to Shin if one side is priced much lower (a heavy favorite).
4. Enter the Kalshi quote to see edge. If Kalshi is trading at 45 cents and the fair is 52, your edge is about 15.5%. Subtract fees to get the real number.

What Devigging Actually Does

When Pinnacle posts 1.91 / 1.91 on a binary market, the raw implied probabilities are 52.36% and 52.36%, summing to 104.71%. That extra 4.71% is the overround, the book's margin. You can't trade at those prices directly because they can't both be right.

Devigging removes the margin and redistributes probability so both sides sum to exactly 100%. The simplest approach is Proportional: divide each raw probability by the sum. For the 1.91 / 1.91 example, 0.5236 / 1.0471 = 50.00%. That matches intuition, the market is a true coin flip.

The output is Pinnacle's best estimate of the true probability, stripped of commission. Since Pinnacle is the sharpest public book, this number is a strong proxy for fair value on any market they cover.

The 3 Methods Compared

Each devig method handles asymmetry differently. Read the full breakdown in our devigging prediction markets guide for the derivations. Here is the short version:

• Proportional: p_A = raw_A / (raw_A + raw_B). Fast, clean, assumes margin is spread equally across both sides. Best for 50/50 markets.
• Shin: Models a portion of the book's volume as coming from insiders and solves for the probability that balances their information advantage. Better when one side is heavily favored.
• Logarithmic: Distributes the overround using log odds, which treats price moves multiplicatively. A middle ground between Proportional and Shin in most practical cases.

For Kalshi and Polymarket where most binary contracts sit within the 20 to 80 cent band, all three methods give similar outputs. The divergence appears on longshots (contracts priced at 5 or 90 cents) where Shin tends to pull more probability toward the favorite.

Why Pinnacle and PS3838

Pinnacle and its offshore sibling PS3838 operate on a low-margin, high-volume model. They take sharp action (they welcome winners instead of limiting them) and let market forces move their line. The result is pricing that sits very close to the true probability on any liquid market.

Other sportsbooks (DraftKings, FanDuel, Caesars) carry 5-10% margin and shade lines toward public bias. Their prices are not suitable as a fair-value reference because the embedded bias is larger than the Kalshi edge you are hunting. Always devig from a sharp book.

From Fair Odds to Kalshi Edge

Once you have fair probability, conversion to cents is direct: multiply by 100 and round. A fair probability of 52.3% becomes 52 cents. If Kalshi's Yes is quoted at 47 cents, your raw edge is 52 - 47 = 5 cents, or about 10.6% on the trade.

Now subtract fees. Kalshi's fee formula peaks around 50 cents and roughly equals 0.07 * price * (1 - price) per contract for the default 7% tier. At a 47 cent entry that's about 1.7 cents of fee, so your net edge is 5 - 1.7 = 3.3 cents, or 7% ROI. That's the number to trade against.

For a structured rule of thumb: target minimum 3% net edge after fees for live trading, 5% or more if you are manually placing orders. The prediction market EV calculator handles the full EV math including Kelly sizing.

Frequently Asked Questions

What is devigging?

Devigging is the process of removing the bookmaker's margin (the vig or juice) from posted odds to estimate the true, fair probability of each outcome. Sportsbooks set prices that sum to more than 100% implied probability so they profit regardless of result. When you devig, you redistribute that overround back to 100% so both sides add up correctly. The output is a fair probability estimate, which you then compare to a Kalshi or Polymarket quote to find edge.

Which devig method is most accurate?

It depends on the market. Proportional (also called Multiplicative) is the simplest and works well for balanced markets where both sides are near 50/50. Shin is considered more accurate when there is asymmetric information (one side is a clear favorite), because it accounts for informed traders distorting the price. Logarithmic sits between the two. For most Kalshi and Polymarket pairings against Pinnacle, running all three methods and using the median gives a robust estimate. The calculator above shows the result for each method so you can cross-check.

Why do Kalshi fees matter when devigging?

Kalshi charges a trading fee that scales with contract price and volume. The default fee tier is roughly 7% of the contract's fill price, though actual fees follow a piecewise formula that peaks around the 50 cent mark. When you calculate fair cents based on a devigged probability, you have to subtract the expected fee to find the price below which you can actually buy profitably. The calculator outputs both the raw fair cents and the fee-adjusted "buy below" price so you know your real break-even.

Can I use this for Polymarket too?

Yes. The devigged probability output is venue-agnostic, so you can apply it to Polymarket by comparing in 0 to 1 price space instead of cents. Polymarket does not charge a trading fee but does have Polygon gas costs per trade, typically around $0.05 to $0.20. For a Polymarket edge calculation, use the fair probability output directly (ignore the Kalshi fee field) and subtract gas as a flat dollar cost from your expected profit per contract.

How does Claw Arbs automate devigging?

Claw Arbs runs devigging live across every matched Kalshi and Polymarket contract against Pinnacle and PS3838 price feeds. The backend calculates fair probability using the selected method every 200 milliseconds, applies Kalshi fee adjustments automatically, and flags any market where the live cents price drops below the fee-adjusted fair price by more than the configured minimum edge threshold. When an edge is detected, the bot can execute both legs across venues in about 20 milliseconds.