Scheduling
The nature of democracy is that elected officials are accountable to the people, and they must return to the voters at prescribed intervals to seek their mandate to continue in office. For that reason most democratic constitutions provide that elections are held at fixed regular intervals. In the United States, elections are held between every three and six years in most states, with exceptions such as the U.S. House of Representatives, which stands for election every two years. There is a variety of schedules, for example presidents: the President of Ireland is elected every seven years, the President of Russia and the President of Finland every six years, the President of France every five years, President of United States every four years.
Pre-determined or fixed election dates have the advantage of fairness and predictability. However, they tend to greatly lengthen campaigns, and make dissolving the legislature (parliamentary system) more problematic if the date should happen to fall at time when dissolution is inconvenient (e.g. when war breaks out). Other states (e.g., the United Kingdom) only set maximum time in office, and the executive decides exactly when within that limit it will actually go to the polls. In practice, this means the government remains in power for close to its full term, and choose an election date it calculates to be in its best interests (unless something special happens, such as a motion of no-confidence). This calculation depends on a number of variables, such as its performance in opinion polls and the size of its majority.
Elections are usually held on one day. There are also advance polls and absentee voting, which have a more flexible schedule. In Europe, a substantial proportion of votes are cast in advance voting.
Read more about this topic: Election, Characteristics