Order Book
Which plays are available entirely on exchanges — where both sides are tradeable market prices rather than a bookmaker's offer — and what those prices really cost once the venue's fee is taken at fill.
The screen, annotated
Every column, and what its number actually means.
Kalshi and Polymarket are not bookmakers. Nobody offers you a price; other traders leave standing offers, and the list of them is the ORDER BOOK. Each rung of that list is a LEVEL: a price, and the SIZE sitting at it — how many contracts someone is actually willing to sell you there. DEPTH is how much size the book holds. A TAKER is someone who accepts an offer already resting on the book, which is what you do every time you place from this screen.
The play's return AFTER the venues' fees. Unlike the sportsbook boards, the number here has already had a real cash cost subtracted from it, which is why it looks so much smaller than a gross figure you might compute yourself. It is a percentage of the money put at risk on the whole position, not of either leg.
The fee line under the card, shown whenever a leg sits on a venue that bills separately. Read it as the deduction that turned 3.09% into the badge above. TWO THINGS ABOUT IT. The fee is charged when your order FILLS, not when the market settles — you pay it whether the contract eventually wins or loses. And it is quoted for a $100 position, because that is the reference size every plan on this board is computed at; at $500 the real fee is five times this.
The two legs. The price shows in whatever odds format you chose in Settings. But an exchange quotes in cents per contract, and that price is just the inverse of the decimal odds: 3.57 decimal is a 28c contract, 1.45 decimal is a 69c contract. Every contract settles at $1.00, so 28c buys a dollar of payout for 28 cents. Thinking in cents is what makes the fee formula legible.
What to put on at that venue. The boxes are linked: type into one and the other resizes so both outcomes pay the same. This is a sizing tool, not an availability check — it will happily plan a $5,000 leg into a level holding $42.
The outcome line under the legs, recomputed live as you type. IT IS BEFORE FEES. It is arithmetic on the two prices only, so on this board it always reads richer than the badge above it, by exactly the fee. The badge is the honest number; this line tells you the shape of the position, not what you keep.
On a low-hold row, what covering BOTH sides costs you — already net of the venues' fees. A positive hold is a price you pay, not a profit: covering both sides of a 1.80% market loses 1.80%. Only a NEGATIVE hold is a locked return. Note the badge on such a row is the hold negated, so it can read as a green pill containing a minus sign — that minus is real.
A middle row. The first line is the two outcomes, the second is the chance of landing in the gap that you need versus the chance the market prices. Exchange middles are rarer than sportsbook ones because both venues are pricing against the same flow, and the fee is charged on both legs whichever way it lands.
Every venue's price on this same line, in place. Open it BEFORE you commit anything. On an exchange it is the only thing here that tells you whether a second-best cover exists, if the leg you planned moves while you fill the first.
When the pair was first seen at these prices. An order book changes whenever anybody trades, so a timestamp several minutes old means the level that created this row has probably already been eaten by somebody else.
The three controls that matter
Ignore everything else on a first read.
Sportsbooks (the chip list at the bottom of Filters)
Tick only the exchanges where you hold a funded, verified account. Funding is slower here than at a sportsbook. A transfer that has not cleared is the same as no account. A row you cannot fill both sides of is not an opportunity — it is a one-sided bet you took by accident.
Min edge %
On this board the figure it filters is already NET of fees, so a floor of 0.5 means half a percent you actually keep. Two warnings. Below roughly 0.5% the edge is thinner than the price move you cause by taking size, so the row is not really there. And any positive floor deletes every low-hold row at once, because a low-hold row's percentage is its hold negated and therefore negative — leave this blank when you are shopping for cheap two-sided markets.
Max quote age (s)
Set it to 30-60, tighter than you would on a sportsbook board. A book price is an offer a company chooses to leave up; an exchange price is one trader's resting order, and it vanishes the moment somebody else takes it. Everything else on the bar — markets, dates, the event picker, the hedge odds bounds — can be left alone on a first read.
A worked example
From a real row to a placed bet, including the stake.
Three things about $0.77. First, that is the trade — not a fraction of it. The 3.09% you can see is available on $145.50 and nowhere else, and the card's stake boxes will not stop you planning ten times that. Second, the fee IS the position. $3.73 of cost against $4.50 of gross edge means five sixths of the opportunity belongs to the venues. And it is charged at fill, so you pay it even on the leg that loses. Both fees peak near 50c a contract and shrink toward the extremes, which is why a pair of mid-priced contracts that looks best on the board is usually the one fees eat whole. Third, 0.53% here against the badge's 0.51% is not a discrepancy. The badge is computed on a $100 reference plan, stakes rounded to whole cents and each fee rounded up. The two drift by hundredths. Trust the badge for ranking and your own arithmetic for the trade you actually place.
When it goes wrong
The price moved, a leg was voided, the row vanished. What to actually do.
You sized in dollars instead of contracts and walked up the book. You wanted $1,000 on the row above, so you took $288.70 of the Kalshi leg — 1,031 contracts — when only 150 were resting at 28c.
Understand what just happened before you do anything else, because the position is not the one the card described. The first 150 filled at 28c for $42.00; the remaining 881 lifted the next level — say 31c — for $273.11. Your 1,031 contracts cost $315.11, an average of 30.6c, not 28c. Against the 69c leg (1,031 shares for $711.39) you have staked $1,026.50 to collect $1,031.00 — $4.50 gross, on which the fees are $15.32 at Kalshi and $11.03 at Polymarket. You have locked a $21.85 LOSS on a row that was genuinely positive at $145. Nothing recovers that once both legs fill, so the work is before. Read the venue's book. Take the size at the level. If you want more of this edge, find another row rather than a deeper level of this one. If only the Kalshi leg is on so far, stop and size the Polymarket leg to the contracts you ACTUALLY hold — 1,031 — not to the plan you started with.
The first leg filled and the second venue's price moved before you crossed. You hold 150 Kalshi contracts at 28c and the 69c on the other side is gone.
You have a directional position you never intended. On an exchange, unlike a sportsbook, you have a real third option: sell the contracts back into the book before the game settles, at whatever someone is bidding. That exit is not free. You cross the spread the other way, and you pay the taker fee a second time — about another $2 on 150 contracts near these prices. So compare three real numbers. The cost of covering on the other side at whatever price exists now (open All books). The cost of selling out of the Kalshi leg. And the cost of holding 150 contracts to settlement, which is $42 at risk. Pick the cheapest deliberately. The failure mode is doing none of the three and discovering at settlement that you had a $42 opinion on a basketball game.
Your order has not filled. It is sitting on the book as a resting offer, and the row is still on the screen.
You placed at the quoted price instead of crossing to take it, so you are now a maker rather than a taker — an offer waiting for somebody else, not a trade. Every number on this board is priced as a taker, because taking is what crossing a spread to capture an edge actually is. An unfilled first leg is harmless: cancel it. An unfilled SECOND leg is the naked-position problem in slow motion, so cancel it and re-take at whatever is currently resting, or unwind the first leg. Do not leave it and check back — the price that fills you eventually will be the one that moved against you.
Common mistakes
The specific ways people lose money with this tool.
Reading the outcome line under the stake boxes as what you keep, because it is bigger and it moves when you type.
It is computed from the two prices alone and subtracts no fee, so on this board it overstates the result by the entire edge and then some. Type $1,000 into the row above and it reads +$30.90. The actual fees on a $1,000 position are about $25.70, so the real figure is roughly $5 — and if the fill is a cent worse than quoted, it is negative. A reader who sizes off that line thinks a marginal trade is six times better than it is.
Treat the green badge as the only net number on the card, and use the outcome line for shape only. For the fee at your size, multiply the fee line by (your stake / $100) — it is quoted for a $100 position. Or compute it: rate x contracts x price x (1 - price) per leg. Kalshi is 0.07, Polymarket sports 0.05.
Taking the whole percentage at whatever size you normally bet, because the price on the card is the price.
The headline price is good only for the size resting at that level. Anything past it fills at the next level, and the next. Your average price ends up worse than the one you clicked. The edge disappears fastest exactly when you take most: the worked example turns a real 3.09% into a locked $21.85 loss by taking seven times the size available. You cannot see this happening from this screen, because nothing here shows depth.
Open the venue's own order book and read the size at the top level before you decide anything. Size the trade in CONTRACTS — the number resting there — and let the dollars fall out of that. If the level is too small to be worth the clicks, skip the row; the next one is a refresh away, and it will still be there at $145.
Treating a low-hold row as an arbitrage because everything on an exchange-only board looks like free money.
A positive hold is the price of covering both sides, not a return. Cover both sides of a 1.80% row and you have paid 1.80% of your stake for the privilege of a guaranteed result — about $18 on $1,000, gone, with no outcome that gives it back. Low hold means cheap, not free.
Place a two-sided cover only when the hold is NEGATIVE — the card will read hold -0.40% and the badge will be positive. Otherwise read a low-hold row for what it is: the cheapest place on the board to take ONE side. Useful when you already have a view, or are covering a position you hold elsewhere.