Why don't bookmaker probabilities sum to 100%?

They sum to slightly more than 100% — the excess is the bookmaker's vig (overround). Typical: 105% on 2-way markets like tennis money line, meaning 5% vig. Subtract the vig to get fair probabilities.

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Odds Converter

Type into any field — every other format updates live. Decimal, American (moneyline), Fractional (UK), Hong Kong, Malay, Indonesian, plus implied probability.

Decimal (EU)

Used in Europe, Australia

American (US)

Moneyline. + underdog, − favourite

Fractional (UK)

Traditional UK

Hong Kong

Decimal − 1

Malay

Asian; sign flips at evens

Indonesian

American ÷ 100

Implied Probability

1 / decimal_odds

Profit on €100 stake

Net win amount

Vig / Overround Calculator (2-way market)

Tennis money-line is a 2-way market — only player A or player B wins. The bookmaker's overround is how much the implied probabilities sum above 100%. Pinnacle: ~2-3%. Soft books: 5-8%. Bet365 on tennis: ~4-6%.

Player A odds (decimal)

Player B odds (decimal)

Enter both odds — overround, fair odds, and bookmaker margin appear here.

Odds format quick-reference

Decimal	American	Fractional	Implied %
1.10	−1000	1/10	90.91%
1.25	−400	1/4	80.00%
1.50	−200	1/2	66.67%
1.75	−133	3/4	57.14%
2.00	+100	1/1 (evens)	50.00%
2.50	+150	3/2	40.00%
3.00	+200	2/1	33.33%
5.00	+400	4/1	20.00%
10.00	+900	9/1	10.00%

Formulas

Decimal → American

if decimal ≥ 2.00: American = (decimal − 1) × 100 if decimal < 2.00: American = −100 / (decimal − 1)

American → Decimal

if American > 0: decimal = 1 + (American / 100) if American < 0: decimal = 1 + (100 / |American|)

Decimal → Implied Probability

implied_p = 1 / decimal_odds

Decimal → Fractional

fractional = (decimal − 1) expressed as a reduced fraction

Related tools

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FAQ

How do I convert American odds to decimal?

Positive American (e.g. +150): decimal = 1 + (150 / 100) = 2.50. Negative (e.g. −200): decimal = 1 + (100 / 200) = 1.50.

What is implied probability?

The probability the bookmaker's odds suggest. Decimal 2.00 → 50%, 1.50 → 66.67%, 3.00 → 33.33%. Compare it to your own probability — if yours is higher, the bet is +EV.

Why do 2-way odds sum above 100%?

The excess is the bookmaker's vig (overround). Typical: 4-6% on tennis money line. Use the vig calculator above to compute the fair (no-vig) probability.

What's "Hong Kong" vs "Indonesian" vs "Malay"?

Hong Kong = decimal − 1 (so HK 0.5 = decimal 1.50). Indonesian = American ÷ 100 (Indo 1.50 = American +150 = decimal 2.50). Malay flips at evens (Malay +0.5 = decimal 1.50; Malay −0.5 = decimal 3.00). All three express the same odds, just in different conventions.

Which format does TIPERO use?

Decimal — the global pro standard. Math is cleanest, EV/Kelly formulas use it directly, and every Pinnacle/Stake/Bet365 trader thinks in decimals.