Moneylines and Percentages

Quick author’s notes to begin:

1) Expert bettor Warren Sharp, who I emailed about on Sunday, went 3-0 in his first week and just dropped his first prop for this week.

Join me in subscribing to get Warren’s plays weekly – this is an investment that should easily pay for itself.

2) I opened up my profile, InsiderOB, to Beta subscribers last week and have been using Juice Reel’s new chat features to talk strategy and share more context behind bets.

The first week is free, I have lots of bets sync’d and am planning video-chat deep dives with subscribers on Kalshi, prediction market betting and lots of other things.

Check me out here if you’re interested!

I’ve been doing more of my betting on exchanges and prediction markets as new options have opened up.

When friends ask how to get started on Kalshi or just want to understand sports betting in more depth, I always begin by teaching them to convert moneylines (or “American odds”) into break-even win percentages.

It’s a simple but essential skill for making sense of prediction markets — and for betting smarter in general.

So today I’ll walk through how to do that, and how sportsbooks built in edge differs from the approach prediction markets take (hint: prediction markets frequently offer better pricing).

As always we’ll look to build on last week’s wins with a new round of “Bets of the Week”.

Let’s get after it. 

Moneylines and Break-Even Percentages

Moneylines themselves aren’t very intuitive.

I presume nearly all of my readers know how they work, but to spell it out:

• A moneyline that starts with a minus sign denotes the amount a bettor would need to wager to win $100.

• So if the line is -200, you bet $200 to win $100.

   

• A moneyline preceded by a plus sign denotes the amount a bettor would win if wagering $100.

• So if the line is +200, you bet $100 to win $200.

In contrast to moneylines, break-even percentages are intuitive.

They tell you exactly how often a team needs to win, or a player needs to hit a milestone, for a bet to be profitable long term.

Here’s the basic math on converting moneylines to break-even win percentages, I’ll denote break-even win percentage with the notation “BE%”:

How to Convert Odds

• Positive odds (underdogs):

  
  Formula: BE% = 100 / (100 + odds)

  
  Example: A +250 underdog has a break-even of 28.6%, calculated as 100 / (100 + 250) = 100 / 350 ≈ 28.6%.

  That means they only need to win 28.6% of the time for you to break even on that bet.

   

• Negative odds (favorites):

  
  Formula: BE% = |odds| / (100 + |odds|)

  (those bars in the formula denote “absolute value,” so make all numbers positive)

  
  Example: a -180 favorite has a break-even of 64.3%, calculated as 180 / (100 + 180) = 180 / 280 ≈ 64.3%.

  They must win almost two out of every three games for you not to lose money.

Once you get the hang of this, you’ll stop looking at raw odds and start thinking in terms of percentages.

This is even more valuable in modern betting, because break-even percentages let you think in probabilities — the same language prediction markets use (more on this later).

I’ll put an easy conversion table in the appendix, and also offer this quick link that’ll do the work for you.

How Sportsbooks Build Their Edge

Sportsbooks make money by shading both sides of a potential bet so the break-even percentages add up to more than 100%. That’s called the hold.

For example, they might offer the following odds on a baseball game:

• Favored Team -160 = 61.5% BE.

• Underdog Team +140 = 41.7% BE.

• Together: 103.2%.

That extra 3.2% is the house edge built into the market. If bettors split action proportionately, the book keeps the difference risk-free.

Prediction markets like Kalshi, by contrast, typically offer much tighter spreads, often summing to a clean 100%.

Here’s an example from tonight’s Marlins-Phillies game:

If Miami trades at 41% (equal to +144), and Philly trades at 59% (equal to -144), the house edge is zero outside of transaction fees.

If I use Juice Reel to find the best line on either side from traditional sportsbooks, I come out worse on both sides – check it out!

My best price on the Marlins is +143, and on the Phillies I can’t do better than -160.

Transaction fees on exchanges vary in a number of unique ways, and are beyond the scope of today’s newsletter, but you can regularly find better pricing for bets like these by shopping exchanges – just like we did here.

PS – Juice Reel now lets you shop pricing for NoVig, ProphetX and Kalshi right in line with other books.

Bet(s) of the Week $$

Last week we kept up the winning (!!).

We played three winless road underdogs and went 2-1 on our wagers, as both the Dolphins and Jets covered the spread before New Orleans was overpowered by Seattle.

We won 0.9 units overall, bringing the running total of bets in this section to 18.6 units, with a positive 19% ROI. We’ll update this regularly.

Based on my research, I am making the following bets this week:

Thursday game

• Seahawks ML @-117 on Kalshi for 1 unit

• Emari Demercado under 15.5 Rush Yards @-125 on Fanatics for 0.5 units

I think the Seahawks look good early. Sam Darnold is PFF’s No. 1 graded QB through three weeks (!!), Seattle’s defense is getting healthier and they’ll have Zach Charbonnet back to complement Kenneth Walker tonight. Arizona is without James Conner, and the matchup tilt plus the injury ledger points to Seattle edging this one in Glendale.

I’ll add the Demercado under because I anticipate Benson monopolizing the early down work, and anticipate the Cardinals playing from behind.

Weekend

• Titans +7.5 @-117 on NoVig for 1 unit

Going back to last week’s trend, the Titans are a “winless road underdog” getting more than a touchdown against an 0-3 Texans team. I am keen to grab the value on this number before we lose it.