The Prediction Markets

Market comparison

Boulter vs Siniakova

2 venues · 18 outcome rows · 1 comparable lines · event identity linked · 0 verified parity · active

Kalshi

Open venue ↗

2 outcomes · $16K reported volume

Observed 15s ago

Recorded venue end date: Nov 7, 2026

Polymarket

Open venue ↗

17 outcomes · $5K reported volume

Observed 1m ago

Recorded venue end date: Oct 31, 2026

Check settlement rules before comparing contracts. Matched outcomes may settle differently. These venues also report end dates more than 48 hours apart; event identity does not mean the contracts close or settle together. These are stored prices; record update times do not certify live quotes. Differences exclude fees and available size.

Known rule differences between venues

  • Postponement: Kalshi resolves to a fair price if the game does not start within 48 hours of the scheduled time (tennis: not finished within two weeks); Polymarket stays open until the game is played and resolves 50-50 only if it is cancelled with no make-up (UFC/tennis: ~14 days).
  • Ties and draws in two-way sports (NFL, college football, UFC no-contest): both venues pay 50/50.
  • Soccer: both settle on 90 minutes plus stoppage time; extra time and penalties excluded.
  • Tennis: 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.
  • UFC: Kalshi ignores result changes after expiry; Polymarket follows the official UFC result.
  • Polymarket two-way moneylines are one contract priced on the first-named side; the other side is its complement (recorded as a derived relation, not a link).

A shared identity alone does not make a price difference executable.

Boulter

Partial parity

Payoffs match in ordinary outcomes; see the rule differences above.

Kalshi

40.0%

Bid 39.0% · Ask 40.0%

Katie Boulter

Open Kalshi ↗

Polymarket

40.0%

Bid 39.0% · Ask 41.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova

Open Polymarket ↗

Price difference 0.0 pp

Completed Match

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

49.0%

Bid 1.0% · Ask 97.0%

Completed Match

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

70.5%

Bid 69.0% · Ask 72.0%

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

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

52.0%

Bid 51.0% · Ask 53.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Match O/U 21.5

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

49.5%

Bid 48.0% · Ask 51.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Game Spread +/-2.5

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

48.5%

Bid 45.0% · Ask 52.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 9.5

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

48.0%

Bid — · Ask 96.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 2 O/U 9.5

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

48.0%

Bid — · Ask 96.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 2 O/U 8.5

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

48.0%

Bid — · Ask 96.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 2 O/U 10.5

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

46.0%

Bid 45.0% · Ask 47.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Match O/U 22.5

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

43.5%

Bid 32.0% · Ask 55.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 2 Winner

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

43.0%

Bid 42.0% · Ask 44.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 Winner

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

41.5%

Bid 40.0% · Ask 43.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Match O/U 23.5

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

40.5%

Bid 39.0% · Ask 42.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Total Sets: O/U 2.5

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

37.5%

Bid 36.0% · Ask 39.0%

Set Handicap: Katerina Siniakova (-1.5) vs Katie Boulter (+1.5)

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

23.5%

Bid 22.0% · Ask 25.0%

Japan Women's Open: Katie Boulter vs Katerina Siniakova Set 1 O/U 10.5

Open Polymarket ↗

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

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

—

Polymarket

23.0%

Bid 22.0% · Ask 24.0%

Set Handicap: Katie Boulter (-1.5) vs Katerina Siniakova (+1.5)

Open Polymarket ↗

Katerina Siniakova

Not aligned

No persisted outcome identity connects these venue contracts.

Kalshi

61.0%

Bid 60.0% · Ask 61.0%

Katerina Siniakova

Open Kalshi ↗

Polymarket

—

Prices are shown as percentages of a $1 payout. “pp” means percentage points. A dash means data is unavailable.

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