D'Hondt formula

The D'Hondt method (mathematically but not operationally equivalent to Jefferson's method) is a highest averages method for allocating seats, and is thus a type of party-list proportional representation. The method described is named in United States after Thomas Jefferson, who introduced the method for proportional allocation of seats in the United States House of Representatives in 1791, and in Europe after Belgian mathematician Victor D'Hondt, who described it in 1878 for proportional allocation of parliamentary seats to the parties. There are two forms: closed list (a party selects the order of election of their candidates) and an open list (voters' choices determine the order).

Proportional representation systems aim to allocate seats to parties approximately in proportion to the number of votes received. For example, if a party wins one-third of the votes then it should gain about one-third of the seats. In general, exact proportionality is not possible because these divisions produce fractional numbers of seats. As a result, several methods, of which the D'Hondt method is one, have been devised which ensure that the parties' seat allocations, which are of course whole numbers, are as proportional as possible. In comparison with the Sainte-Laguë method, D'Hondt slightly favours large parties and coalitions over scattered small parties.

Legislatures using this system include those of Albania, Argentina, Armenia, Austria, Belgium, Brazil, Bulgaria, Cambodia, Cape Verde, Chile, Colombia, Croatia, Czech Republic, Denmark, Dominican Republic, East Timor, Ecuador, Estonia, Fiji, Finland, Guatemala, Hungary, Iceland, Israel, Japan, Kosovo, Luxembourg, Macedonia, Moldova, Montenegro, Netherlands, Paraguay, Peru, Poland, Portugal, Romania, Scotland, Serbia, Slovenia, Spain, Turkey, Uruguay, and Wales.

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