How to Convert Prediction Market Prices to American Odds

A professional bettor in Las Vegas sees Polymarket showing 65% on the Chiefs to win the Super Bowl. His usual sportsbook has them at -186. Same number? Different format? He needs to convert to compare apples to apples and spot if one side is offering value the other isn't.

Prediction markets like Polymarket and Kalshi display probabilities as percentages. Traditional sportsbooks use American moneyline format. If you read +150 and -200 regularly, percentages feel abstract. Converting them lets you use the same mental shortcuts you already have. More importantly, it lets you compare pricing across platforms to find edge.

Why Sports Bettors Need This Skill

November 2025: a sharp bettor noticed Polymarket had the Philadelphia Eagles at 52% to make the playoffs. Converting that to American odds gave him -108. His offshore book had the same bet at -135. He confirmed Polymarket had $50K+ depth before entering the position. The prediction market was offering better value by nearly 30 cents on the dollar. He took the Polymarket side, then hedged on the sportsbook when the odds converged two weeks later. The arbitrage came from speaking both languages.

If you read American odds regularly, you know what they signal. DraftKings shows +150, that's an underdog paying $150 profit on a $100 bet. FanDuel lists -200, a heavy favorite requiring $200 risked to win $100.

Prediction markets don't speak that language natively. Polymarket shows "58¢" or "58%" on a binary outcome. Kalshi displays similar probability-based pricing. But the underlying math is identical to what sportsbooks use. The difference is presentation.

Research tracking sports-related prediction markets on Kalshi found that pricing discrepancies of 5% or more from traditional sportsbooks appear approximately 18% of the time, but most discrepancies exist for under 10 minutes before markets converge. Without conversion, those opportunities are invisible.

Understanding this translation is one of the practical skills we cover across our how-to guides for working with prediction markets effectively.

The Conversion Formulas (Step-by-Step)

The process requires two steps: convert percentage to decimal odds, then decimal odds to American format. The formulas split depending on whether you're looking at a favorite (above 50%) or underdog (below 50%).

For Favorites (Probability Above 50%)

Step 1: Convert percentage to decimal

• Take your percentage and divide by 100
• Example: 65% becomes 0.65

Step 2: Calculate decimal odds

• Formula: 1 ÷ probability decimal
• Example: 1 ÷ 0.65 = 1.538

Step 3: Convert to American odds

• Formula: -100 ÷ (decimal odds - 1)
• Example: -100 ÷ (1.538 - 1) = -100 ÷ 0.538 = -186

The negative sign indicates this is a favorite. You'd need to risk $186 to win $100.

For Underdogs (Probability Below 50%)

Step 1: Convert percentage to decimal

• Example: 35% becomes 0.35

Step 2: Calculate decimal odds

• Formula: 1 ÷ 0.35 = 2.857

Step 3: Convert to American odds

• Formula: (decimal odds - 1) × 100
• Example: (2.857 - 1) × 100 = 1.857 × 100 = +186

The positive sign indicates an underdog. A $100 bet would profit $186.

Worked Examples Across the Range

Common conversion reference points that bettors encounter regularly:

Notice how the steeper the probability (75%), the more you risk relative to potential profit (-300 means risk $300 to win $100). The lower the probability (20%), the higher your potential return (+400 means risk $100 to win $400).

These conversions assume zero vig, the raw mathematical relationship between probability and odds, which is exactly what prediction markets attempt to display. As covered in what the price means in prediction markets, the percentage represents crowd consensus on likelihood.

Using Online Calculators (When You Don't Want Math)

Nobody wants to divide decimals on their phone while watching a game. Online odds converters handle this instantly. For pre-match comparison, they're essential.

Recommended calculators:

1. OddsAssist (oddsassist.com) — Built specifically for prediction market conversion. Enter probability, get American odds instantly.
2. Pinnacle Odds Converter (pinnacle.com/en/betting-articles/educational/odds-converter) — Industry standard. Handles American, decimal, fractional, and implied probability. Clean interface.
3. AceOdds Calculator (aceodds.com) — Converts all formats bidirectionally. Shows breakeven percentages alongside conversions.

Step-by-step walkthrough using OddsAssist:

1. Go to the prediction market odds converter
2. Find the "Probability %" field
3. Enter your market percentage (example: 58)
4. The American odds field auto-populates (-138)
5. Bookmark the page, you'll use it constantly

Pro tip: These tools work bidirectionally. If you want to verify a sportsbook's odds are correct, enter the American odds and check if the implied probability matches what you calculated mentally. Sportsbooks sometimes shade lines based on public betting action. If DraftKings shows -145 but the fair line should be -130, you're seeing betting pressure baked into the price.

Common Issues and What They Mean

The Vig Problem

Polymarket shows 52% on Team A. You convert: -108. But DraftKings has Team A at -115. That's not the same number. What happened?

Answer: Juice. Sportsbooks build commission into both sides of a market. Add up implied probabilities on both sides of a traditional betting line. They sum to more than 100%, often 104-107%. That's the vig, the house cut.

Prediction markets show something closer to raw crowd belief. A 52% on Polymarket reflects where actual buyers and sellers agreed to trade, minus a small transaction fee. There's still a gap between what you can buy at and what you can sell at, but it's not a built-in house edge on both sides.

Practical meaning: If converted odds differ by more than 3-4 points, one platform might offer value. If Polymarket converts to -108 and your book is -130, the prediction market is offering better pricing, assuming both have adequate liquidity.

When Percentages Don't Add to 100%

You see a Polymarket binary market: "Yes" at 52%, "No" at 49%. That's only 101%. In multi-outcome markets, you might see three options summing to 96% or 104%.

Why this happens: The gap between buying and selling prices. The 52% might be what you'd pay to buy "Yes" shares right now. The 49% is what someone is willing to pay to buy "No" shares. Market makers profit from that gap.

Does it break the conversion formula? No. Convert each percentage independently. Understand that you can't arbitrage by buying both sides, the spread accounts for that.

When it matters: If spreads are wide (5%+), the market has low liquidity. Your execution price might differ from the displayed price.

The 50% Exact Case

A market sits at exactly 50.0%. Converting gives you +100, also written as EVEN. This means risk $100 to win $100, a coin flip in betting terms.

You rarely see exactly 50% on active prediction markets. Liquidity and order flow push prices to 49% or 51% constantly. If you do see 50%, it usually means the market opened recently or volume is extremely low.

Extreme Probabilities

What if Polymarket shows 5% on an outcome? Converting: 1 ÷ 0.05 = 20.0 decimal odds. Then (20 - 1) × 100 = +1900. That's a 19-to-1 underdog.

At 95%? That's 1 ÷ 0.95 = 1.053 decimal. Then -100 ÷ (1.053 - 1) = -1900. Rarely worth the capital tie-up even if you're highly confident.

Extreme odds reveal liquidity issues. A sportsbook might never post -1900 because the capital requirement is absurd. Prediction markets will show it because there's a thin order book. But if you tried to place a large bet at 95%, you'd move the market. Actual execution might be 92% or 93%.

Frequently Asked Questions

What's the fastest way to convert prediction market percentages to American odds?

For probabilities above 50%, divide negative 100 by (decimal odds minus 1). For probabilities below 50%, multiply (decimal odds minus 1) by 100. First convert your percentage to decimal odds by dividing 1 by the probability. For example, 65% becomes 1 ÷ 0.65 = 1.538 decimal odds, then -100 ÷ 0.538 = -186 American odds. Most bettors bookmark an odds calculator like OddsAssist or Pinnacle's converter for instant results without manual math. Once you've done the conversion a few times, common percentages (60%, 40%, 70%) become automatic mental references.

Why do Polymarket odds look different from DraftKings lines on the same game?

Prediction markets display raw crowd consensus probabilities with minimal built-in house edge, while sportsbooks add "vig" (juice) to both sides of every bet. If you add the implied probabilities from both sides of a traditional betting line, they sum to 104-107% instead of 100%. That extra percentage is the sportsbook's commission. Polymarket's 52% converts to -108, but DraftKings might show -130 on the same outcome because they've built profit margin into the line. Discrepancies of 5+ points may indicate value on one platform. Sportsbooks also shade lines based on where public money is flowing, while prediction markets reflect pure supply and demand between traders.

Can I use the same conversion formula for political markets and sports betting?

Yes, the mathematical relationship between probability and American odds is identical regardless of the event type. Whether you're converting Kalshi's Fed rate decision contract at 38% or Polymarket's Super Bowl odds at 65%, the same formulas apply: above 50% uses -100 ÷ (decimal odds - 1), below 50% uses (decimal odds - 1) × 100. The only difference is context. You're applying sports betting intuition to non-sports events, which is exactly what makes prediction markets powerful for cross-domain comparison. A bettor comfortable evaluating NFL spreads can use that same probability-assessment skill on election outcomes or economic indicators once odds are in familiar format.

What does it mean when a prediction market shows exactly 50%?

A market at exactly 50% converts to +100 (EVEN) in American odds, meaning risk $100 to win $100, a pure coin flip. You rarely see precisely 50% on active markets because continuous trading pushes prices to 49% or 51%. When you do see 50%, it typically indicates a newly opened market with minimal volume or a genuinely uncertain outcome where the crowd is perfectly split. At EVEN odds, there's no mathematical edge unless you believe the true probability differs from 50%. In practice, most markets hover around 48-52% when outcomes are legitimately uncertain, with the spread accounting for the gap from exact 50%.

How do I know if converted odds represent actual value or just different formatting?

Conversion translates format but doesn't validate accuracy. You still need to assess whether the probability itself is correct. If Polymarket shows 45% (converting to +122) but your analysis suggests 60% is the true probability, that's potential value regardless of format. Compare converted odds across multiple platforms: if Polymarket converts to +122 and your sportsbook offers +105 on the same outcome, the prediction market is offering better pricing assuming adequate liquidity. Value exists when your estimated probability exceeds what the odds imply, not simply because one number looks bigger than another. Sharp bettors develop their own probability models, then use conversion to identify when market prices diverge from those models by meaningful margins.

What to Do With This Skill

Spotting Mispriced Markets

If you believe the true probability of an outcome is 60%, but a prediction market shows 45%, you've found potential edge. At 45%, the implied American odds are +122, meaning the market is paying you as if the event is less likely than you think.

This is how sharp bettors think. They don't ask "Will this win?" They ask "Is the current price mispriced relative to the true probability?" Conversion lets you translate your probability estimate into expected value math.

Example from the 2024 NFL season: A bettor analyzing weather data believed snow in Buffalo created a 55% chance of the under hitting. The local sportsbook had the under at +105 (implied 48.8%). Polymarket, aggregating broader opinion, showed 47% on the under. Converting: +113 implied odds. Both platforms underpriced the weather edge. He bet both, weighted toward the better line. Final score: 13-10, under hit. The edge came from converting percentages to odds and comparing them to his own probability model.

Comparing Across Platforms

January 2026: Kalshi had "Will the Fed cut rates in March?" at 38%. Converting: 1 ÷ 0.38 = 2.632 decimal, then (2.632 - 1) × 100 = +163. A financial derivatives platform was offering the equivalent Fed decision bet at +140. Same event, different pricing. The Kalshi side offered better value.

A trader who could read both formats spotted the discrepancy. He took Kalshi at 38% (implied +163) and hedged part of the position on the derivatives platform at +140. When the Fed announced no cut, he collected on Kalshi's "No" shares. Had the Fed cut, his hedge limited downside. The entire opportunity existed because he converted percentages to odds automatically.

For more context on how prediction markets generate these prices and what drives movements, see our guide to prediction markets, which covers the fundamentals of how these platforms aggregate information.

Understanding Value vs. Price

American odds make value intuitive. If you see +200, you know immediately that a $100 bet profits $200. If someone offers you +250 on the same outcome, that's objectively better.

Percentages are harder to parse. Is 35% better than 33%? Converting to odds (+186 vs. +203) makes the value difference concrete. The +203 side pays $17 more per $100 risked.

This matters for bankroll management. If you're betting a fixed percentage of your roll based on Kelly Criterion, you need to know the exact payoff structure. American odds give you that instantly. For more on making decisions like this, see can you make money on prediction markets.

Cross-Sport and Cross-Domain Comparisons

One underrated use: comparing sports betting odds to non-sports prediction markets. Kalshi offers political event contracts. Polymarket has crypto milestones. If you're comfortable evaluating NFL spreads, you can apply the same probability-to-odds logic to "Will Bitcoin hit $100K by year-end?"

A bettor in New Jersey, experienced with NBA player props, noticed Polymarket had "Luka Doncic MVP" at 22% in December 2024. Converting: +355 implied odds. DraftKings had Doncic at +320. The prediction market was offering worse value, suggesting the crowd on Polymarket was less sharp on NBA futures than dedicated sportsbooks. He took DraftKings, avoided Polymarket. Doncic didn't win MVP, but the point is process: conversion revealed pricing inefficiency.

Common Mistakes to Avoid

1. Confusing decimal odds with American odds in calculators If you enter 1.65 in the "American odds" field, you'll get nonsense. Always use the correct input field or convert manually.

2. Forgetting the negative sign on favorites 65% should convert to -186, not +186. The sign matters for bankroll math. If you calculate payouts wrong, you'll missize bets.

3. Ignoring liquidity when placing orders The displayed percentage might be 40%, but if the spread is wide, your actual execution could be 38% or 42%. Always check depth before assuming you're getting the shown price.

4. Assuming converted odds equal fair odds Polymarket shows 58% (-138) doesn't mean -138 is the "true" line. That's the current market clearing price. You still need to evaluate if the market itself is mispriced.

5. Mixing up probability with percentage of bankroll A 40% chance of winning doesn't mean bet 40% of your roll. Probability determines odds. Position sizing is separate math (usually Kelly Criterion or fixed fractional).

When Conversion Matters Most

Arbitrage Hunting

If you're comparing Polymarket to offshore books like Bovada or BetOnline, conversion is mandatory. You can't eyeball whether 56% is better value than -130. Convert both to American odds, compare directly.

Live Betting

Odds move in real-time. If you're live-betting a political event on Kalshi while watching odds shift on a betting exchange, you need instant mental conversion. Sharp traders often memorize a conversion table for common percentages. 60% equals -150. 40% equals +150. 55% equals -122.

Portfolio Hedging

If you're holding multiple positions across platforms, you need to know your aggregate exposure in a consistent format. Converting everything to American odds lets you see if you're overexposed to one side of a market.

A trader in Miami held $1,000 worth of "Yes" shares on Polymarket at 60% (bought earlier at 55%). He wanted to hedge by betting "No" on a sportsbook. Without converting, he couldn't calculate the right hedge size. He converted: 60% equals -150. That let him calculate that betting $600 on the opposite side at +140 would create a nearly risk-neutral position.

Next Steps: Building Fluency

Practice with real markets. Open Polymarket and Kalshi side-by-side. Pick five active contracts. Convert the percentages to American odds manually. Then check your work with a calculator. Do this daily for a week and conversion becomes automatic.

Learn the reverse direction. If someone gives you American odds, you should be able to convert back to implied probability instantly. The formulas run backward: for negative odds, divide the odds by (odds + 100). For positive odds, divide 100 by (odds + 100).

Compare platforms live. Find the same event priced on Polymarket, Kalshi, and a traditional sportsbook. Convert everything to American odds. Note the discrepancies. They're typically within 2-3 points. When they're not, investigate why. That's where edge lives.

Understanding conversion is the bridge between sports betting intuition and prediction market opportunity. Once you internalize what +150 means, you can apply that same instinct to any probability-based market: politics, crypto, economic indicators. The moment you translate percentages into the language you speak fluently, everything clicks.

For a deeper dive into how these probabilities are generated and what they represent, see how prediction markets work. To understand the difference between prediction market prices and traditional betting lines, read prediction markets vs betting.