What Are Alternate Lines? The Prop Ladder, Explained

An alternate line is the same bet at a different number.

If a hitter’s total bases prop sits at 1.5, the book will usually also offer 0.5, 2.5, 3.5 and up. Same player, same stat, same game — just a different bar to clear, priced to match. Lower the bar and the Over gets more likely and pays less. Raise it and the Over gets less likely and pays more.

That’s the whole idea. The interesting part is what the ladder tells you about the market underneath it.

Main line first, ladder around it

Most props have a main line — the number the book considers the fair midpoint, priced closest to a coin flip. It’s the one you see first, and it’s the one the book most wants balanced action on.

The alternates hang off it in both directions. In our capture of MLB batter props on August 21, 2026, DraftKings posted 1,416 main-line hits props and 1,970 alternates around them — so for every “real” line there were more than one alternate rungs stacked nearby.

The practical read: the main line is the market’s estimate. The rungs are priced off it. A longer price further up the ladder isn’t the book being generous; it’s the same estimate expressed at a less likely threshold.

Home runs skip the main line entirely

Here’s the part that confuses people, and it’s specific to certain markets.

On the same day, across the same batter props, DraftKings posted zero main-line home run props. Not few — zero. All 1,503 of its home run props were alternates.

That isn’t a gap in our data. The same book flagged main lines on every other batter market that day: 1,416 on hits, 1,218 on hits+runs+RBIs, 924 on singles, 900 on runs, 594 on total bases. Home runs was the one market with none.

So a home run market isn’t “Over/Under 0.5 home runs” with alternates around it. It’s a ladder all the way down:

• 1+ home runs (the 0.5 rung)
• 2+ home runs (1.5)
• 3+ home runs (2.5)

Three rungs, no centre. That’s why the market reads as milestones rather than as a line, and why you’ll rarely see it written as an Over/Under at all.

Why the rungs usually only go one way

Because a main line is a genuine two-way market and a rung isn’t.

A book posts both sides of a main line because it wants money on either side of its estimate. An alternate rung is a different product — it exists for someone who wants a longer price on the same player. The demand it serves is Over demand, so the Over is what gets posted.

Follow that through to home runs and the answer falls out: no main line means no two-way market, which means no Under. That day, DraftKings and FanDuel posted 1,503 and 1,203 home run Overs respectively and not one Under between them.

It isn’t universal, though, and that’s worth knowing. Hard Rock posted the same three rungs two-sided — 934 Overs and 934 Unders. Same stat, same day, same three numbers, a completely different menu. Whether an Under exists is a decision each book makes, not a property of the bet.

What this changes when you’re reading a board

• No Under next to a number is the tell. You’re looking at a rung, not the line. And if the market has no main line at all, as home runs often doesn’t, there’s no line to find.
• Don’t compare a rung to another book’s main line. Two books showing different first numbers may be a real disagreement — or one may just be leading with a different rung. Compare like for like.
• A longer price is a longer shot. The ladder isn’t offering value as you climb it. It’s offering a different risk, priced accordingly.
• The same market can look different everywhere. As above: one book’s one-way ladder is another’s two-sided menu.

If you want the same mechanic in a sport where the main line does exist — and what happens to the Under above and below it — WNBA prop ladders walks through a market where a book’s own data marks which line is the main one.

And if you specifically want the lower side of a threshold that no book will post, that side always exists on an exchange, because a contract needs someone on both ends. What it costs is a separate question, covered in the prediction markets guide.

For how often a number has actually been beaten rather than what it costs to bet, the MLB props pages show each market’s recent frequencies, rung by rung.