Best MLB Arbitrage Platforms in 2026: Fees, Rainouts and the Postseason Postponement Window

The quick answer

Cheapest MLB leg before first pitch: Novig. No fee for maker or taker on pre-game straight trades.

Cheapest pre-game taker fee after Novig: Kalshi. It halved its taker fee on MLB series on 7 August 2026, and its order book is public.

Closest settlement match to a sportsbook: ProphetX. A rainout is voided with collateral returned, and run lines and totals need 8.5 innings, the same as DraftKings.

Best if you post rather than take: Polymarket US. Makers collect a rebate.

Most expensive: DraftKings Predictions, at 2c per contract between 30c and 94c, each time you open or close.

What breaks MLB arbs: a postponed game that one venue voids and another keeps open, a rain-shortened game that voids a run line on one side and settles it on the other, and a sportsbook "listed pitcher" bet against a prediction market contract that has no pitcher condition.

On the $200 pre-game example below, Novig keeps the whole $6.14 edge and a Kalshi taker pays about $1.80.

What MLB arbitrage is

You back both sides of an MLB market on two venues at prices that together guarantee a return, whichever team wins. Most US positions pair a sportsbook leg with a prediction-market leg.

Baseball has no draw in a full game, so a moneyline arb needs two legs. It also has rainouts, and every venue writes its own rules for postponed and rain-shortened games.

How we checked

This covers venues a US bettor can open and get an MLB position filled on. Fees and settlement rules come from each platform's own schedule, contract terms or house rules, opened again on 7 October 2026.

Kalshi's MLB fee applies the 0.5 multiplier in Kalshi's public fee-change data to the standard formula in its fee schedule, checked 7 October. Depth comes from Kalshi's public market data. The World Series is scheduled to open on 23 October, with a potential Game 7 on 31 October.

The platforms, ranked for MLB arbitrage

This order follows the fee on the pre-game leg. On rainout settlement, ProphetX would rank first, and on visible depth, Kalshi.

1. Novig: the cheapest pre-game leg

Novig charges no fee to either side on a pre-game straight trade. In-game, takers pay 0.03 x price x (1 - price) per contract, and makers pay nothing on any trade type.

Novig runs on Ludlow Exchange, LLC, a CFTC Designated Contract Market. Its MLB Winner and Prop contracts were certified on 23 July 2026 and its Spread and Total contracts the next day, and its help center lists single-game winner, run line, total, first five innings, YRFI/NRFI, team totals and player props.

We found no public depth data for Novig's MLB menu, so test a fill at your size first. Its help center lists it as unavailable in Arizona, Michigan and Nevada.

Best for: the prediction-market leg of a pre-game arb on sides, run lines and totals.

2. Kalshi: half-price taker fee, public order book

Kalshi's public fee data shows its MLB game, run line and total series moved to a 0.5 taker multiplier on 7 August 2026. Applied to its standard 0.07 x price x (1 - price), that's about 88c per 100 contracts at 50c. The game-winner series also charges the resting side a maker fee.

On postseason games, its game-winner markets tended to show tight spreads and more size than the run lines and totals on the same games.

Best for: filling size, and the cheapest pre-game taker leg after Novig.

3. ProphetX: settles weather like a book

ProphetX takes 2% of net gains per market on straight trades, so a position held to settlement pays only on the winning leg. Its baseball rules void every contract, with collateral returned, if a game doesn't start on its scheduled day. Run lines and totals need nine innings, or 8.5 if the home team leads, and moneylines become official after five innings, or 4.5. Those are the thresholds DraftKings uses.

Best for: the second leg of an arb on a day with rain in the forecast.

4. Polymarket US: paid to post

Polymarket US's taker coefficient has been 0.0695 since 1 October 2026, which is $1.74 per 100 contracts at 50c. Makers are paid $0.31 per 100 at the same price. Polymarket US changed some fees again on 7 October 2026, so check its current schedule before relying on these figures.

Its sports FAQ keeps a postponed game live if it's rescheduled before the contract expires, typically two weeks after the original date, and settles every MLB market on the official score of a game called early. Check the app for which MLB markets it has open before you plan a leg there.

Best for: the resting side of an arb.

5. DraftKings Predictions: the costliest leg

DraftKings' own fee disclosure lists $0.02 per contract per side for prices from 30c to 94c, so you pay to open and again if you close early. It's available in a limited set of states, and its MLB menu can differ from the other venues here, so check the app for yours.

Best for: bettors where it's available who already hold a DraftKings Predictions account and nothing else.

The sportsbook leg

A sportsbook such as FanDuel, DraftKings or BetMGM usually supplies the other leg, with its vig already inside the price. Several offshore books and exchanges aren't open to US bettors.

What an MLB arb keeps after fees

A pre-game moneyline arb on one game: a sportsbook leg at decimal 2.04 (+104) on one team and a prediction-market leg at 48c on the other. Stake $100.98 at the book and buy 206 contracts for $98.88. Total outlay is $199.86, either result pays $206.00, and the profit before fees is $6.14.

Where MLB arbs break

Postponements, and the October window

DraftKings voids every bet on a game that doesn't start on its scheduled date, and ProphetX does the same. Kalshi keeps the market open if the game starts within 48 hours of the original start time, postseason included. Novig's window is 48 hours in the regular season and 45 days for a playoff game, and Polymarket US waits until the contract expires, typically two weeks.

So a postseason game rained out and played the next day refunds a DraftKings ticket and leaves a Novig or Kalshi position live. In the example above, the book returns $100.98 and you hold 206 unhedged contracts that cost $98.88.

Rain-shortened games

Every venue checked settles the moneyline on an official game, which MLB declares after five innings, or 4.5 with the home team ahead. DraftKings and ProphetX void run lines and totals below 8.5 innings and return the stake. Polymarket US settles them on the official score when the game is called, and Kalshi at its last fair market price. Novig voids them and settles at a fair value taken from the 30 minutes of trading before the stoppage.

A total arbed between DraftKings and Polymarket US in a game called after seven innings refunds one leg and grades the other.

Listed pitchers

Sportsbooks offer some baseball markets with a named starter. DraftKings lists projected pitchers for information only, so its standard bets have action whoever starts, but a "Pitcher Must Start" market is voided if the named starter doesn't take the mound. Novig's MLB contracts settle on the result regardless of any pitcher change, and Kalshi's game terms carry no pitcher condition. Pair a pitcher-must-start ticket with a prediction market and a late scratch leaves you holding one side.

Run line against moneyline

A run line arbs only against the opposite run line. Taking Team A -1.5 at a book and Team B on the moneyline elsewhere loses both legs when Team A wins by exactly one run. On Kalshi, the No side of "Team A wins by over 1.5 runs" covers Team B +1.5.

Extra innings and the first five

Full-game markets include extra innings at DraftKings, Kalshi, Novig and ProphetX. First-five-innings markets don't, and a tie after five settles differently. DraftKings pushes a two-way bet with no tie option. Novig pays each side 50c, and so does Kalshi when it lists no tie outcome.

What to look for

Fee on the prediction-market leg: with no pre-game fee the example keeps $6.14, and a Polymarket US taker keeps about $2.57. On Novig that window closes at first pitch.

Weather: check the forecast, and read both venues' postponement windows before you build a position.

Market type: arb moneylines on rain days, since run lines and totals split on shortened games.

Pitcher terms: match an action bet with an action bet.

Depth: test fills where you can't see the book.

Your state: sports contracts are restricted or litigated in several states, and the list changes with court rulings.

MLB arbitrage FAQ

What platform is best for MLB arbitrage?

Novig is the cheapest pre-game leg, with no fee to either side. Kalshi has the lowest pre-game taker fee of the rest after halving its MLB fee in August 2026, and ProphetX matches DraftKings' rules on rainouts and short games.

When does the 2026 World Series start?

MLB has scheduled Game 1 for 23 October 2026 and a potential Game 7 for 31 October.

Sources

Checked 7 October 2026 except where noted.

Novig fee schedule: support.novig.com/en/articles/16195057-fees-on-novig

Novig Fair Value Settlement: support.novig.com/en/articles/16163706-what-is-fair-value-settlement-fvs

Novig sports and markets, contracts list and eligibility: support.novig.com articles 10336189, 16083642 and 16194031

Novig MLB contract terms: ludlowexchange.com/filings (MLB Winner and Prop certified 23 July 2026; Spread and Total 24 July 2026)

Kalshi MLB fee-change log: Kalshi public API (KXMLBGAME, KXMLBSPREAD, KXMLBTOTAL; series fee changes)

Kalshi contract terms: BASEBALLGAMEWIN, BASEBALLSPREAD and BASEBALLTOTALS

Kalshi fee schedule: kalshi.com/docs/kalshi-fee-schedule.pdf (effective 7 July 2026)

Polymarket US fee schedule and sports FAQ: docs.polymarket.us/fees (effective 1 October 2026); docs.polymarket.us/faqs/sports-faqs

ProphetX Baseball Rules and Understanding Fees: ProphetX help center, updated 6 October and 19 August 2026

DraftKings Predictions fee disclosure: myaccount.draftkings.com fee-disclosure (Predictions, standard pricing)

DraftKings Sportsbook house rules, baseball section: Massachusetts Gaming Commission filing, implementation date 26 August 2025

2026 postseason schedule: MLB press release, "MLB announces 2026 Postseason schedule"