Combo Edge Builder
Build a same-game combo from this week's NFL slate, see what it's really worth, and walk in with your own number. Never take a quote below it.
Watch: three correlated legs priced at 22.1%, not 17.4%
Thirty seconds on the whole idea — three Ravens legs off one game, the naive product a parlay calculator returns, the true joint probability from the scoreline model, and the fair-value band the quote gets graded against.
The worked example in the clip
| Leg | Market | Fair |
|---|---|---|
| Ravens ML (BAL to win) | 64¢ | 66% |
| Ravens team total over 23.5 | — (model-priced) | 58% |
| L. Jackson 250+ pass yards | 47¢ | 47% |
- Naive multiply, 64% × 58% × 47% → 17.4%
- True joint (Σ P(margin, total) over every scoreline where all three legs resolve YES) → 22.1%, a +27% correlation bonus
- Fair multiplier 4.52x, band ±15% → 3.93x – 5.32x
- Quoted 5.6x → above the band → SMASH, EV +24%, quarter-Kelly 1.3% of bankroll
Transcript
- “Three legs, one game. They move together.”
- “Multiply them like a parlay calculator? 17.4%.”
- “Sum every scoreline where all three hit: 22.1%.”
- “That is a fair band of 3.9x – 5.3x.”
- “Your platform quotes 5.6x. Above the band — SMASH.”
Use the Combo Edge Builder inside your AI agent
This tool is also live on our MCP server as combo_edge. Connect Claude, ChatGPT, Cursor, or Copilot and call it directly — six core calculators are free.
Method notes ▾
Quick Answer
This free builder prices Kalshi same-game combos against their true joint probability and gives you your number before you ask: the lowest multiplier worth accepting at break even, +5%, +10% or +20%, Kalshi fee included. Kalshi combos are quoted privately by a market maker, so you request the combo, type the quote you get back, and the tool says whether it clears your number, falls short, or should be declined — with Win%, the correlation lift, and flags for impossible and redundant legs.
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Related Tools
What is the Kalshi Combo Edge Builder?
It is a correlation-aware same-game combo (SGC) builder for Kalshi — the equivalent of a same game parlay tool, but built for an exchange that has no parlay product. You pick legs from the live board, stack them into a slip, and the builder shows what the combo should pay (fair odds), the correlation lift, and your number — the lowest multiplier worth accepting — so you know it before you request a quote. Type the quote that comes back and it tells you whether it clears your number. For what combos pay back on average at DraftKings, see the DK Tape.
How to use it
Sort the board by edge, add two or more same-game legs to the slip, and read the correlation bonus and EV. Same-game legs are where the value lives — cross-game legs are independent and carry no bonus. On NFL, the combo that actually moves together is a moneyline plus that same team's total over (say Ravens ML + Ravens team total over 23.5); a moneyline plus a game total is close to independent. Size any position you take with the built-in quarter-Kelly suggestion, and pair it with the EV Calculator. Got independent, uncorrelated legs instead? Use the Kalshi Parlay Calculator — it multiplies the legs, which is exactly right when they don't come from the same match.
How the Combo Edge Builder works
For every game on the board, the builder reads a scoreline model — a per-game joint distribution over every possible final score. For NFL that is a margin × total distribution on the integer score lattice — centred on a market-anchored fair line, with a logistic margin shape fitted to a decade of closing lines. Every leg you can pick is just a condition on that scoreline — a Ravens moneyline, a Ravens team total over, a game total under — so the leg probabilities and the combo probability all come from the same distribution and never contradict each other.
Where a Kalshi contract is listed — moneylines, the point-spread ladder, the game-total ladder, player props — the board shows its live price, our raw model number, and a fair number that leans on the market, with the edge as fair minus market. Our game model does not beat the closing line on its own, so the fair number starts from where Kalshi's own spread and total ladders cross 50% and stays there — the model publishes as a lean beside it, not as a shift to the line. Where no contract exists — NFL team totals — the leg is marked as a model price and the market column reads “—”. We do not synthesize a price for a market that does not exist.
When you stack legs from the same match, the builder sums the probability of every scoreline where all of your legs hit at once — the exact, correlation-aware joint probability. It compares that to the naive product of the leg probabilities (what a no-correlation tool would show) and reports the difference as the correlation bonus.
Grading your combo quote
Kalshi's same-game combos are priced by a market maker as a private quote (an RFQ), and other platforms' same-game parlays are quoted with a correlation adjustment baked in — either way, the only price you can actually take is the one your platform quotes for the whole combo. This builder turns the model's joint probability into your number — the lowest multiplier worth accepting at a target return, fee included, built on the cautious end of the fair-value band — and checks the quote against it: clears your number, short of it, or decline. The product of the individual leg prices is not a purchasable price — no venue pays it on legs that settle at the same time — so we show it only as a theoretical assemble ceiling, never as the number to grade against. Negative-correlation pairs are the trap: the true joint is below what the price implies, so they are marked in red.
Frequently Asked Questions
Can I combine player props with game lines on Kalshi?
Yes, and the correlation between them is the whole point. Pick an NFL game in the builder and its listed player props load alongside the moneyline and totals, both sides of every contract. A receiving-yards contract and its own team total move together — when that offence scores, the receiver almost always got there with it — so multiplying the two probabilities the way every other tool does gets the joint wrong in the same direction every time. The builder conditions each prop on the game script — pace (the total) and flow (the margin) — inside the same scoreline model it prices the game legs with, so the combined Win% reflects how the legs actually move. Kalshi lists props game by game through the week, so early in a week only some games have them.
Why is my all-unders combo worth more than the parlay calculator says?
Because the unders all need the same thing — a low-scoring game — and a parlay calculator multiplies them as if they were unrelated. Four unders across both teams in one game are not four separate calls; they are one call on the game script, and when it lands they all land. The builder prices each prop conditional on that script (the total for pace, the margin for flow) and sums the probability of every scoreline where all the legs hit at once, so the combo's Win% comes out higher than the naive product and the fair multiplier comes out lower. It also means they lose together: one shootout and the whole slip is gone. The Win% and the Kelly line already account for both.
Why does Fair lean on the market?
Because our game model does not beat the closing line on its own, and we would rather show you that than hide it. On every game leg the builder shows three numbers: the market's devigged price, our raw model number, and a fair number that starts from the market's own spread and total ladders and moves a quarter of the way toward our model (a fifth on totals). The edge is fair minus market. Before this change the edge was model minus market, and a 4-point spread disagreement read as a 15-point probability edge — most of which was our error, not the market's. Player props are different: the prop model passes its own backtest, so its probabilities are not shrunk.
What does MKT mean on a player prop leg?
MKT means the probability shown is Kalshi's own price with the spread removed, not a separate call of ours. We have no independent view on that contract, so the edge column shows a dash rather than a number — a zero would read as "we checked and it is fair", which is a different and stronger claim than "we have no view". A market-priced leg is not a lesser leg: it still goes into the correlation-aware joint, and doing that joint correctly on the market's own numbers is the part almost nothing else does. Most listed strikes are market-priced.
Why can't I stack two thresholds on the same player?
Because on the same side they are one position, not two. NO on 40+ rushing yards already contains NO on 50+ — anything that keeps him under 40 keeps him under 50 — so selecting both pays a second premium for one outcome and the builder blocks it. The same holds in the other direction: YES on 50+ already implies YES on 40+. Opposite sides are different, and they are allowed: YES on 40+ together with NO on 50+ is a genuine range position, that he finishes between 40 and 49 yards. The builder allows that pair and prices it.
What is the Combo Edge Builder?
The Combo Edge Builder is a correlation-aware same game parlay (SGP) tool for Kalshi. It computes the true joint probability of your legs from a per-game scoreline model — a market-anchored margin/total lattice over every final score — so same-game legs that move together are priced correctly, not naively multiplied — turns that into a fair-value odds band, and grades the price your platform quotes against it: above the band is a real edge, inside is fair, below is a pass. If you want the simpler independent-leg math instead, use the free Kalshi Parlay Calculator, which multiplies uncorrelated legs. Use the Combo Edge Builder whenever your legs come from the same game.
Can you do a same game parlay on Kalshi?
Yes — Kalshi now offers same-game combos as a dedicated multi-leg market, but the price is quoted privately by a market maker (an RFQ quote) rather than posted on a public orderbook, so you only see it once you request it. This builder is the fair-value benchmark for that quote: it computes the combo's true joint probability from a scoreline model and turns it into a fair-value odds band. You paste the multiplier your platform actually quotes, and the tool grades it — a quote longer than fair value is a real edge, a quote inside the band is fair, and a quote shorter than fair value is a pass. It is the number to check any combo quote against before you take it.
How do I know if a Kalshi combo quote is worth taking?
Walk in with your number before you ask. Once you have two or more legs in the slip, the builder shows the lowest multiplier worth accepting at four targets — break even, +5%, +10% and +20% return — with the Kalshi taker fee included by default. The ladder is built on the cautious end of the combo's fair-value range (the correlation-aware joint probability minus a model-uncertainty margin, because a multi-leg joint is never one exact number), so clearing it means the quote beats our number even if we are a little optimistic. Then request the combo on Kalshi and type the quote you get back (4.6x, +360 or 22¢): the builder says Clears your number, Short of your number (still +EV, just under your target) or Decline (under break-even). Kalshi combos are quoted privately by a market maker and you cannot post your own price, so declining and requesting again is how you shop — quotes refresh, and a different maker may answer.
What if the combo is a pass but I still like the legs?
Build it leg by leg. Under your number the builder lists a limit price for every leg that carries its own edge — the highest resting bid that still returns your target at the cautious end of that leg — so you can make the market yourself on each contract instead of taking the combo quote. Buying legs separately gives up the correlation lift, which is why the combo is the first answer when the quote clears your number.
What is a correlation bonus?
The correlation bonus is how much more likely your combo is to hit than a naive multiply of the individual leg probabilities would suggest. We compute the true joint probability from a per-game scoreline grid (an exact distribution over every possible final score) and compare it to the product of the marginals. If the joint probability is 33% but multiplying the legs gives 26%, the correlation bonus is about +27%. Cross-game legs are independent, so their bonus is zero — the bonus only appears on same-game legs, which is exactly where the Kalshi mispricing lives.
What do Clears your number, Short of your number and Decline mean?
They are the three answers to a quote you typed in, checked against the target you picked on your-number ladder. Clears your number: the quote pays at least the multiplier your target needs, so take the fill and size it off quarter-Kelly. Short of your number: the quote is still +EV at the cautious end of our range, just thinner than your target — take the thinner edge or decline and request again. Decline: the quote is under break-even, so you would be paying the maker; walk away or drop the weakest leg. The expected return is shown at both the cautious end and the centre of our range, with the Kalshi fee included unless you switch it off. Agents calling the combo_edge MCP tool also get the older seven-tier verdict (SMASH through RUN AWAY) for back-compat.
Is the Combo Edge Builder free?
Yes — the whole tool is free. Stack up to 6 legs, see Win%, the correlation lift, your number (the lowest multiplier worth accepting, fee included) and — once a quote comes back — whether it clears your number, with no paywall and no account required. There is an optional, skippable email signup for edge alerts, but nothing in the tool is gated behind it.
Which NFL legs can I combine?
For each game on the current NFL slate the builder offers both moneylines, every rung of Kalshi's game-total ladder as an Over and an Under, every rung of the point-spread ladder as both sides, every rung of each team's points ladder as an Over and an Under, and the game's listed player props — all priced off one scoreline model, so the per-leg numbers and the combo number never disagree. Moneylines, spreads, game totals and team totals carry a live Kalshi price and a fair value anchored on it; a side Kalshi has not listed yet shows our number with an explicit "model" marker rather than an invented market price. Team totals and props are where the NFL correlation bonus actually lives — a moneyline plus that team's total over move together, and a stack of unders all need the same low-scoring game — while a moneyline plus a game total is close to independent. Stack up to 6 legs within one game or across games, all free.
Can you parlay NFL games on Kalshi?
Yes — Kalshi offers same-game combos as a dedicated multi-leg market, but the price comes back as a private market-maker quote (an RFQ) rather than a posted orderbook price, so you only see it once you request it. You can also just buy each leg as its own contract. Either way this builder is the benchmark: it computes the combo's true joint probability from the NFL scoreline model and turns it into a fair-value odds band, so when a quote comes back you can tell immediately whether it is above fair value, inside the band, or a pass.
Why does a parlay calculator underprice same-game legs?
Because it multiplies the legs as if they were independent. Three legs from one game are not: if Baltimore wins, the team total is more likely to clear, and a higher total means more Lamar Jackson passing volume. Multiplying 64% x 58% x 47% returns 17.4%. Summing the probability of every scoreline in which all three legs resolve YES returns 22.1% for the same three legs — a 27% correlation bonus a parlay calculator cannot see. That gap is the entire reason this tool prices off a scoreline model instead of a product.
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