There are two types of odds quoted on betting exchanges — back and lay odds, whereas traditional bookmakers work only with back odds. Taking a lay position on outcome 1 is equivalent to taking a back position on outcomes X2 (double chance bet). Accordingly, taking a lay position on outcome 2 is equivalent to taking a back position on outcomes 1X. Since laying an outcome can be regarded as backing the alternative outcomes, lay odds can be converted into equivalent back odds. This calculator finds that equivalent, also taking into account the commission charged by the exchange.
The odds in the formula are in decimal format.