Overround and margin calculator

Outcome one decimal odds Outcome two decimal odds Outcome three decimal odds Outcome four decimal odds, optional

Example result

2.00, 3.50 and 4.00 imply a 3.57% overround.

What this calculator answers

Add a set of decimal prices to measure the implied total. The calculator reports the overround and rescales the implied probabilities to produce proportional fair odds.

Formula and worked example

Formula: Overround percent = (sum of 1 divided by each decimal price minus 1) multiplied by 100. Fair probability = raw implied probability divided by the implied total.

Prices of 2.00, 3.50 and 4.00 imply 50.00, 28.57 and 25.00 percent, or 103.57 percent in total. Removing that proportional margin gives fair decimal odds of about 2.07, 3.63 and 4.14.

Checks before using the result

• Adding decimal prices instead of inverse probabilities.
• Assuming margin is distributed equally in every market.
• Comparing fair odds from different outcome sets.

When the calculation does not apply

The fair odds are a proportional adjustment, not an estimate of true event probability. Markets can shade outcomes unevenly.

Keep the number in context

A calculator shows the arithmetic. It doesn't tell you whether the price fits your read of the outcome or your budget. Decide the stake before you enter it. Check the market rules. Keep essential money out of it entirely.

Cross-check on a second tool. The calculator hub, Kelly criterion or Poisson football score cover the same numbers from a different angle. Same price conventions, so a decimal price in one is a decimal price in the other.

Read the guide to reading odds if you're new to the formats. Two minutes.

Reading a rounded result

Money is rounded to two decimals here. A real settlement applies its own rounding sequence, which can differ. Keep the original inputs written down if you're going to check the number later.

Unclear about an input? Find the stated market term. Don't guess. A quick sanity check: change one input by a small amount and see whether the result moves the way you expect.

That doesn't validate the market. It can flag a reversed sign, a mis-entered price format or a duplicated stake. Use the number to understand the arithmetic. It's not a reason to ignore a limit you set in advance.