On a betting exchange there are two types of odds quoted - back and lay odds whereas traditional bookmakers deal only with back odds. Taking a lay position on outcome 1 is equivalent to taking a back position on outcomes X2 (double chance bet). Respectively 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 taking also into account the commission charged by the exchange.