+150 or -110. Must be ≤ -100 or ≥ +100.
American
-110
Decimal
1.91
Fractional
91/100
Implied probability
52.38%
What these odds say the true win chance is, before the book's margin.
Payout on a $100.00 stake
$191.00
$91.00 profit + your $100.00 stake back.
Reference implementation
The exact conversion this calculator runs. American odds are only defined at |value| ≥ 100 — the positive and negative formulas meet at the +100/-100 boundary, both equal to decimal 2.00. Copy this straight into your own app.
- · No API key required — it's just arithmetic
- · Decimal odds are the internal pivot for every conversion
- · Full source (fractional + payout too) linked in the comment
// American <-> decimal odds, the reference implementation this
// calculator runs. Fractional, implied probability, and payout use the
// same decimal pivot — see bigballsdata.com/tools/odds-calculator.
function americanToDecimal(american: number): number {
return american >= 100 ? 1 + american / 100 : 1 + 100 / Math.abs(american);
}
function decimalToAmerican(decimal: number): number {
// decimal 2.00 (the +100/-100 boundary) always resolves to +100.
return decimal >= 2 ? Math.round((decimal - 1) * 100) : Math.round(-100 / (decimal - 1));
}
function impliedProbability(decimal: number): number {
return 1 / decimal; // 0-1; multiply by 100 for a percentage
}What this is (and isn't)
This is a documented reference implementation for odds arithmetic — the same conversions our odds documentation references, published as a standalone tool. It doesn't show live sportsbook lines, link to a sportsbook, or take a stake for real money — every number here is one you type in, converted on your device. If you need live odds data behind this math, that's what the API is for.
Frequently asked
- How do I convert American odds to decimal odds?
- For positive American odds (e.g. +150), decimal = 1 + (American / 100). For negative American odds (e.g. -110), decimal = 1 + (100 / |American|). Both formulas agree at the +100/-100 boundary, which is always decimal 2.00 (evens). This calculator does the conversion live as you type.
- What is implied probability in betting odds?
- Implied probability is the win chance an odds price represents, before the sportsbook’s built-in margin (vig). It’s 1 / decimal odds, shown as a percentage. Decimal 2.00 (evens, or American +100/-100) implies a 50% chance.
- How do I calculate payout from odds and stake?
- Total payout = stake × decimal odds. Profit = total payout − stake. A $100 stake at decimal 2.50 (American +150) returns $250 total: your $100 stake back plus $150 profit.
- Why is there no American odds value between -99 and +99?
- American odds are only defined at or beyond the +100/-100 threshold by design — there is no "+50" or "-50" American price. Positive American odds show profit on a $100 stake; negative American odds show the stake needed to profit $100. Both scales start at 100.
- Is this calculator free, and does it store my inputs?
- Yes, fully free with no signup, and it runs entirely in your browser — the numbers you type never leave your device or hit our servers. It’s a pure client-side reference implementation, not a live odds feed.
Need the live odds behind the math?
This calculator is free forever, no key required. When you're ready for real sportsbook lines, scores, and stats behind it, the API has a free tier too.
1,000 req/day free (2,000 with GitHub). No credit card.