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New · Polymarket & Kalshi tools

Prediction markets,
spoken in odds you understand.

Polymarket and Kalshi quote events in cents — a contract at 65¢ means the market prices the event at 65%. Bettors think in decimal odds. These tools bridge the two worlds: convert prices, spot arbitrage between prediction markets and sportsbooks, and track your positions.

$150B+
combined lifetime volume
~80%
of Kalshi volume is sports
$8.6B
sector volume, Apr 2026
678k
monthly Polymarket users

Contract price ↔ odds converter

Enter a prediction market price in cents (0–100). See it as probability and in every odds format bettors use.

¢
Contract price
what you pay per share
65¢
Implied probability
market's view of the chance
65.0%
Decimal odds
European / standard format
1.538
American odds
US moneyline
-186
Fractional odds
UK format
27/50
A YES contract at 65¢ returns $1 if the event happens — a 35¢ profit on 65¢ risked, which is decimal 1.54. Buying NO would cost 35¢ for the same $1 payout if it doesn't.

Prediction market ↔ sportsbook arbitrage

Back YES on a prediction market and the opposite outcome at a sportsbook. If their combined implied probability is under 100%, you lock in profit regardless of the result.

55.0% implied
43.5% implied · opposite outcome
across both legs
Arbitrage found · +1.52%
Combined implied probability: 98.48% (under 100% = guaranteed profit)
Buy YES (PM)
$558.50
Bet opposite (book)
$441.50
Locked profit
+$15.45
Real arbs are tight and short-lived. Account for prediction-market fees and bid/ask spread (see the Fees tab), and remember sportsbooks may limit winning accounts. This assumes a clean binary market with no draw.

Position profit & loss

You bought shares at an entry price. See your P&L if you sell now at the current price, or hold to resolution.

Cost basis (100 shares × 40¢) $40.00
Sell now at 65¢
Sale value
$65.00
Profit / loss
+$25.00
ROI
+62.5%
Resolves YES
+$60.00
+150% · each share pays $1
Resolves NO
-$40.00
−100% · shares expire worthless
The edge of prediction markets: you don't have to wait for resolution. If your entry at 40¢ rose to 65¢, selling locks profit now — useful when news has already moved the price your way. Log these trades in your journal.

Fees & spread cost

The quoted price isn't your real cost. You buy at the ask (higher), and platforms may charge fees. See your true effective entry price.

Mid price
65.0¢
Spread
2.0¢ · 3.1%
Fee cost
$10.00
Effective entry price
What you really pay per share after spread + fees
67.32¢
You buy 758 shares at the 66¢ ask for $500.00, plus $10.00 in fees. Your breakeven shifts from the 65.0¢ mid to 67.32¢ — the hidden cost of trading.
Fee models differ: Kalshi charges per-contract fees that scale with price, while Polymarket has historically had no trading fees but takes them on resolution. Always check current terms — and factor spread into any arbitrage.

Prediction markets vs traditional betting

Price = probability
A contract trading at 65¢ pays out $1 if the event happens. That price is the market's implied probability: 65%. Divide 1 by the price (0.65) and you get decimal odds of 1.54.
You can exit early
Unlike a fixed bet, you can sell your position before the event resolves. If you bought YES at 40¢ and it climbs to 70¢, you can lock in profit without waiting for the outcome — like trading a stock.
Peer-to-peer, not vs the house
There's no bookmaker setting the line. Prices come from supply and demand between traders. This means margins can be tighter — but also that arbitrage against sportsbooks is possible when the two disagree.
Beyond sports
Politics, economics, crypto prices, weather, culture — prediction markets cover anything with a verifiable outcome. Sports is the largest category, but the breadth is far wider than any sportsbook.

Why cross-market arbitrage exists

Prediction markets and sportsbooks price the same events independently. A sportsbook sets its line based on its risk model and customer flow; a prediction market price emerges from traders. When they disagree enough, you can back one outcome on the prediction market and the opposite at a sportsbook, locking in profit regardless of result.

Example: a prediction market has YES at 55¢ (55% implied). A sportsbook offers the opposite outcome at decimal 2.30 (43.5% implied). Together that's 98.5% — under 100%, leaving a 1.5% locked margin. The Arbitrage Finder tab does this math and splits your stakes automatically. For traditional two-bookmaker arbs, see our arbitrage calculator.

Regulatory note: Prediction market availability and legal status vary by jurisdiction. Kalshi is CFTC-regulated in the US; Polymarket International is not, and some US states have challenged these platforms. These tools are educational and don't constitute financial or legal advice. Always verify what's permitted in your region, and gamble responsibly — see our responsible gambling page.