The Prediction Markets

Japan Women's Open: Katie Boulter vs Katerina Siniakova

Starts in 6 hKickoff
Traded
$22K
Venues
Polymarket, Kalshi
Prices updated
just now
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What the markets expect

Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5 70%

Next is Katerina Siniakova at 61%. Polymarket and Kalshi agree within 1 point on each matched outcome.

Odds by venue

Consensus blends each venue’s last price, weighted by how much has traded there. Best Yes price is the cheapest ask across venues, and the payout is what a winning $100 stake returns before fees. Open a row for each venue’s contract name, bid and ask, and how closely their rules match.

Prices come from our regular polls of each venue. Ages are as of when this page was built.

  • Polymarket
  • Kalshi
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
70%
Polymarket 70%polled, 34s agoBest Yes 71¢ on Polymarket, $100 pays $141 (1.41x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
Last price
70%
As of
Polled just now
Buy Yes
71¢
Sell Yes
69¢
$100 on Yes pays
$141 (1.41x)
Trade this on Polymarket
Katerina Siniakova
61%
Kalshi 61%polled, 34s agoBest Yes 61¢ on Kalshi, $100 pays $164 (1.64x)
Kalshi
Contract
Katerina Siniakova
Last price
61%
As of
Polled just now
Buy Yes
61¢
Sell Yes
60¢
$100 on Yes pays
$164 (1.64x)
Volume
$14K
Trade this on Kalshi
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
52%
Polymarket 52%polled, 34s agoBest Yes 53¢ on Polymarket, $100 pays $189 (1.89x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Match O/U 21.5
Last price
52%
As of
Polled just now
Buy Yes
53¢
Sell Yes
51¢
$100 on Yes pays
$189 (1.89x)
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
50%
Polymarket 50%polled, 34s agoBest Yes 51¢ on Polymarket, $100 pays $196 (1.96x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Game Spread +/-2.5
Last price
50%
As of
Polled just now
Buy Yes
51¢
Sell Yes
49¢
$100 on Yes pays
$196 (1.96x)
Trade this on Polymarket
Completed Match
49%
Polymarket 49%polled, 34s agoBest Yes 97¢ on Polymarket, $100 pays $103 (1.03x)
Polymarket
Contract
Completed Match
Last price
49%
As of
Polled just now
Buy Yes
97¢
Sell Yes
1¢
$100 on Yes pays
$103 (1.03x)
Volume
$100
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
48.5%
Polymarket 48.5%polled, 34s agoBest Yes 52¢ on Polymarket, $100 pays $192 (1.92x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 9.5
Last price
48.5%
As of
Polled just now
Buy Yes
52¢
Sell Yes
45¢
$100 on Yes pays
$192 (1.92x)
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
48%
Polymarket 48%polled, 34s agoBest Yes 96¢ on Polymarket, $100 pays $104 (1.04x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 2 O/U 10.5
Last price
48%
As of
Polled just now
Buy Yes
96¢
Sell Yes
—
$100 on Yes pays
$104 (1.04x)
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
48%
Polymarket 48%polled, 34s agoBest Yes 96¢ on Polymarket, $100 pays $104 (1.04x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 2 O/U 8.5
Last price
48%
As of
Polled just now
Buy Yes
96¢
Sell Yes
—
$100 on Yes pays
$104 (1.04x)
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
48%
Polymarket 48%polled, 34s agoBest Yes 96¢ on Polymarket, $100 pays $104 (1.04x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 2 O/U 9.5
Last price
48%
As of
Polled just now
Buy Yes
96¢
Sell Yes
—
$100 on Yes pays
$104 (1.04x)
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
45.5%
Polymarket 45.5%polled, 34s agoBest Yes 46¢ on Polymarket, $100 pays $217 (2.17x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Match O/U 22.5
Last price
45.5%
As of
Polled just now
Buy Yes
46¢
Sell Yes
45¢
$100 on Yes pays
$217 (2.17x)
Trade this on Polymarket
Show 8 more outcomes
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
43%
Polymarket 43%polled, 34s agoBest Yes 44¢ on Polymarket, $100 pays $227 (2.27x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 Winner
Last price
43%
As of
Polled just now
Buy Yes
44¢
Sell Yes
42¢
$100 on Yes pays
$227 (2.27x)
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
42%
Polymarket 42%polled, 34s agoBest Yes 43¢ on Polymarket, $100 pays $233 (2.33x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Match O/U 23.5
Last price
42%
As of
Polled just now
Buy Yes
43¢
Sell Yes
41¢
$100 on Yes pays
$233 (2.33x)
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
41%
Polymarket 41%polled, 34s agoBest Yes 44¢ on Polymarket, $100 pays $227 (2.27x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 2 Winner
Last price
41%
As of
Polled just now
Buy Yes
44¢
Sell Yes
38¢
$100 on Yes pays
$227 (2.27x)
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
40.5%
Polymarket 40.5%polled, 34s agoBest Yes 42¢ on Polymarket, $100 pays $238 (2.38x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Total Sets: O/U 2.5
Last price
40.5%
As of
Polled just now
Buy Yes
42¢
Sell Yes
39¢
$100 on Yes pays
$238 (2.38x)
Trade this on Polymarket
Boulter
38.7%
Polymarket 38.5%polled, 34s agoKalshi 39%polled, 34s agoBest Yes 39¢ on Polymarket, $100 pays $256 (2.56x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova
Last price
38.5%
As of
Polled just now
Buy Yes
39¢
Sell Yes
38¢
$100 on Yes pays
$256 (2.56x)
Volume
$5K
Trade this on Polymarket
Kalshi
Contract
Katie Boulter
Last price
39%
As of
Polled just now
Buy Yes
39¢
Sell Yes
38¢
$100 on Yes pays
$256 (2.56x)
Volume
$3K
Trade this on Kalshi
Partial parity

Payoffs match in ordinary outcomes; see the rule differences below the table.

No arbitrage: the best bid elsewhere is 38¢, at or below the cheapest ask of 39¢.

Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
38%
Polymarket 38%polled, 34s agoBest Yes 39¢ on Polymarket, $100 pays $256 (2.56x)
Polymarket
Contract
Set Handicap: Katerina Siniakova (-1.5) vs Katie Boulter (+1.5)
Last price
38%
As of
Polled just now
Buy Yes
39¢
Sell Yes
37¢
$100 on Yes pays
$256 (2.56x)
Volume
$31
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
23.5%
Polymarket 23.5%polled, 34s agoBest Yes 25¢ on Polymarket, $100 pays $400 (4.00x)
Polymarket
Contract
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 10.5
Last price
23.5%
As of
Polled just now
Buy Yes
25¢
Sell Yes
22¢
$100 on Yes pays
$400 (4.00x)
Trade this on Polymarket
Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
22.5%
Polymarket 22.5%polled, 34s agoBest Yes 24¢ on Polymarket, $100 pays $417 (4.17x)
Polymarket
Contract
Set Handicap: Katie Boulter (-1.5) vs Katerina Siniakova (+1.5)
Last price
22.5%
As of
Polled just now
Buy Yes
24¢
Sell Yes
21¢
$100 on Yes pays
$417 (4.17x)
Trade this on Polymarket

No cross-venue arbitrage right now: on every matched outcome, the best bid on one venue is at or below the cheapest ask on the other. Find markets with open spreads

Mostly the same bet: two differences

Where they differ

  • If the match is postponed: Kalshi resolves to a fair price if the match does not start within 48 hours of the scheduled time (tennis: not finished within two weeks); Polymarket stays open until the match is played and resolves 50-50 only if it is cancelled with no make-up (tennis: ~14 days).
  • Kalshi requires a ball to be played and pays the winner; Polymarket pays the player who advances, including on retirement. A pre-match walkover is a fair price on Kalshi, 50-50 on Polymarket.
Polymarket
Polymarket resolves via:
UMA optimistic oracle, source: wtatennis.com
Kalshi
Kalshi resolves via:
Kalshi (CFTC-regulated exchange), source: WTA
Show full rule comparison
  • If the match is postponed: Kalshi resolves to a fair price if the match does not start within 48 hours of the scheduled time (tennis: not finished within two weeks); Polymarket stays open until the match is played and resolves 50-50 only if it is cancelled with no make-up (tennis: ~14 days).
  • Kalshi requires a ball to be played and pays the winner; Polymarket pays the player who advances, including on retirement. A pre-match walkover is a fair price on Kalshi, 50-50 on Polymarket.
  • Trading closes Oct 31, 2026, 4:30 AM UTC on Polymarket and Nov 7, 2026, 3:00 AM UTC on Kalshi.

Summarized from each venue’s published rules; the venue’s own rules page is the final word.

How the odds have moved

The top 3 outcomes on both venues, with the consensus between them. Hover for exact values.

  • Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5
  • Katerina Siniakova
  • Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5

Order books

Each venue’s resting orders for the selected outcome’s Yes contract, side by side. Top of book streams live; depth refreshes every 15 seconds.

Polymarket

Open on Polymarket ↗

Top of book

Connecting
Best bid
—
Spread
—
Best ask
—

Waiting for the first live quote…

Depth · top 8 levels

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Recent trades

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Kalshi

Kalshi doesn’t list Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5 for this event.

What your stake buys

Enter a stake to see where it buys the most after fees, using each venue’s live order book.

$
Buy

Loading both order books…

Buys at the asks resting now (taker orders), cheapest after fees first, from order-book snapshots up to 15 seconds old. Fees: Kalshi 0.07 × price × (1 − price) per share, rounded up to the cent; Polymarket 0.05 × price × (1 − price) per share (sports rate). Fee calculator. Estimates only, not advice.

About this market

Live prediction market odds for "Japan Women's Open: Katie Boulter vs Katerina Siniakova". Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 8.5 leads at 70%. Next is Katerina Siniakova at 61%. $22K has traded across 18 outcomes on Kalshi and Polymarket. The market is expected to resolve by Oct 31, 2026.

This market refers to the tennis match between Katie Boulter and Katerina Siniakova in the Japan Women's Open, originally scheduled for October 24, 2026 at 12:30AM ET. This market will resolve to 'Katie Boulter' if Katie Boulter advances against Katerina Siniakova. This market will resolve to 'Katerina Siniakova' if Katerina Siniakova advances against Katie Boulter. If the match is canceled (not played at all), ends in a tie, or a winner has not been determined by November 7, 2026, 11:59 PM ET (14 days after the scheduled start), this market will resolve to 50-50. If the match begins but is not completed, and one player advances due to the opponent's retirement, default, or disqualification, this market will resolve to the player who advances. If the match ends in a walkover (player withdraws before the start and the other advances automatically), this market will resolve to 50-50. The primary resolution source will be official information from the WTA Tour. A consensus of credible reporting may also be used.

Questions

What does the consensus price mean?

It is the price of a Yes contract that pays $1 if the outcome happens. A 14¢ price means traders put the chance near 14%. Where two venues list the same outcome, we blend their last prices, weighting the venue with more trading volume more heavily (neither counts for less than a quarter). When only one outcome can win, each venue’s prices add up to a little over 100% (its margin); the fair chance removes that margin so the outcomes add up to exactly 100%.

How is the payout worked out?

A Yes contract pays $1 if it wins, so at the best ask a $100 stake buys 100 ÷ ask contracts. At 18¢ that is about 555 contracts, paying $556 (5.56x) if Yes happens. Venue fees and price slippage on larger orders are not included.

Why do the venues show different prices?

Each venue has its own traders, fees and order book. Contracts can also settle on slightly different terms, which is why each row lists how closely the rules match.

Is a price gap an arbitrage?

Only when you can buy Yes on one venue below what someone pays for Yes on the other, after fees, and both contracts settle the same way. We show the executable bid and ask so you can check.

How fresh are these prices?

Venue prices refresh every few minutes, and the order book and live quotes stream continuously. Each venue’s card shows when we last observed it.

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