Decimal Odds for MLB Strikeout Props: A UK Bettor’s Conversion Guide
Available in US
The First Time -110 Made No Sense to Me
I grew up with decimal odds. Backing a 2.00 selection means doubling your money if you win. Simple, clean, intuitive. Then I started analysing MLB K props using American sources, and every line was listed as -110, +150, -130. The format felt deliberately obstructive, like someone had designed it to confuse outsiders. It took me a week of forced practice before the conversions became automatic – and now I switch between formats without thinking. But that first week was rough, and I know from conversations with other UK bettors that the American odds format is the single biggest barrier to entry for baseball prop betting.
The UK sports betting market – generating roughly 2.48 billion pounds in annual gross gambling yield – operates almost exclusively in decimal odds. Every Premier League match, every horse race, every tennis prop is priced in decimals. American MLB content, however, publishes everything in American format. If you want to follow US-based K-prop analysis, compare prices across markets, or even understand the laddering strategy that uses +150, +300, and +750 tiers, you need to think fluently in both formats.
The Conversion Formulas
There are two formulas, one for negative American odds and one for positive. Once you memorise both, conversion takes about three seconds.
For negative American odds (the favourite side), the formula is: decimal odds = 1 + (100 / absolute value of the American odds). Take the most common K-prop price, -110. The calculation is 1 + (100 / 110) = 1 + 0.909 = 1.91. So -110 in American format equals 1.91 in decimal. A 10-pound bet at 1.91 returns 19.10 (including your stake), for a profit of 9.10. The heavier the favourite (larger negative number), the closer the decimal approaches 1.00. For example, -200 = 1 + (100/200) = 1.50. And -300 = 1 + (100/300) = 1.33.
For positive American odds (the underdog side), the formula is: decimal odds = 1 + (American odds / 100). Take +150, a common alt-line price. The calculation is 1 + (150 / 100) = 1 + 1.50 = 2.50. A 10-pound bet at 2.50 returns 25.00 (including stake), for a profit of 15.00. Bigger positive numbers mean bigger payouts: +300 = 1 + (300/100) = 4.00. And +750 = 1 + (750/100) = 8.50.
The reverse conversion – decimal to American – is occasionally useful when you want to communicate with US-based analysis. For decimal odds below 2.00: American = -100 / (decimal – 1). So 1.91 becomes -100 / 0.91 = -110. For decimal odds at or above 2.00: American = (decimal – 1) x 100. So 2.50 becomes 1.50 x 100 = +150.
Common K-Prop Lines in Both Formats
Rather than converting every line from scratch, it helps to memorise the most frequently encountered K-prop prices. Here are the ones you will see almost daily during the MLB season.
The standard K-prop line – over or under at -110 – converts to 1.91 decimal. This is the baseline price where the sportsbook has built in roughly 4.5% vig. When the line moves slightly, you will see -115 (1.87 decimal) or -105 (1.95 decimal). These small shifts reflect line movement based on betting action or updated information.
Alt lines above the standard produce the plus-money prices that make laddering attractive. Over at +150 = 2.50 decimal. Over at +200 = 3.00. Over at +300 = 4.00. Over at +500 = 6.00. Over at +750 = 8.50. Each step represents a higher K threshold with a correspondingly larger payout.
Alt lines below the standard are priced as heavier favourites. Over at -150 = 1.67 decimal. Over at -180 = 1.56. Over at -200 = 1.50. Over at -250 = 1.40. These lines set lower K thresholds that are more likely to hit but return less profit per unit risked.
If your UK platform displays odds in fractional format rather than decimal – some still do – the conversions from American are: -110 = 10/11 fractional = 1.91 decimal. +150 = 3/2 fractional = 2.50 decimal. +300 = 3/1 fractional = 4.00 decimal. Most UK bettors find decimal cleaner for comparison purposes, and I recommend setting your platform to decimal display if you have the option.
Implied Probability: What the Odds Tell You
Converting odds to implied probability is the step that turns format literacy into analytical utility. Implied probability tells you what the sportsbook believes is the likelihood of the outcome occurring, before you apply your own analysis.
For decimal odds, the conversion is simple: implied probability = 1 / decimal odds. So 1.91 implies 1 / 1.91 = 52.4%. And 2.50 implies 1 / 2.50 = 40.0%. And 4.00 implies 1 / 4.00 = 25.0%. The sum of implied probabilities for both sides of a K prop will always exceed 100% – the excess is the vig, the sportsbook’s margin.
Understanding implied probability is critical for identifying value. If you believe the true probability of a K over is 58%, and the sportsbook’s implied probability is 52.4% (odds of 1.91), the 5.6-percentage-point gap is your edge. If you believe the true probability is 53%, the gap narrows to 0.6 points – not enough to justify a bet given the uncertainty in your estimate. Every K-prop bet should start with this comparison: your estimated probability versus the implied probability. If your number is not higher than the book’s number, the bet is not +EV regardless of how good the matchup looks on paper.
One formatting tip that saves time: when comparing K-prop prices across multiple UK platforms, convert everything to implied probability rather than comparing decimal odds directly. The difference between 1.87 and 1.91 does not jump off the screen, but the difference between 53.5% and 52.4% – a full percentage point of implied probability – makes the value gap immediately visible. For a deeper exploration of how to calculate expected value from odds differences and when the edge justifies a bet, the pillar guide on MLB strikeout prop bets covers the complete EV framework.
What is -110 in decimal odds?
The American odds -110 converts to 1.91 in decimal format. The formula is 1 + (100 / 110) = 1.91. A 10-pound bet at 1.91 returns 19.10 total (9.10 profit plus your 10-pound stake). This is the standard price on most K-prop over/under lines, with the sportsbook’s vig built into the sub-2.00 pricing on both sides.
How do I convert plus-money American odds to decimal?
For positive American odds, the formula is 1 + (American odds / 100). So +150 becomes 1 + 1.50 = 2.50 decimal. +300 becomes 4.00. +750 becomes 8.50. These are the prices you encounter on alt strikeout lines, where higher K thresholds carry bigger payouts. Memorise the common conversions (+150 = 2.50, +300 = 4.00) and you will read US-based K-prop analysis without needing a calculator.
Created by the ”mlb Strikeout Prop Bets” editorial team.
