In voting, a ballot is considered spoilt, spoiled, void, null, informal, invalid or stray if a law declares or an election authority determines that it is invalid and thus not included in the vote count. This may occur accidentally or deliberately. The total number of spoilt votes in a United States election has been called the residual vote. In Australia, such votes are generally referred to as informal votes, and in Canada they are referred to as rejected votes.
In some jurisdictions spoilt votes are counted and reported.
A ballot may be spoilt in a number of ways, including:
As an example, UK law specifically precludes ballots "on which votes are given for more candidates than the voter is entitled to vote for", "on which anything is written or marked by which the voter can be identified" or "which [are] unmarked or void for uncertainty".
If a voter makes a mistake while completing a ballot, it may be possible to cancel it and start the voting process again. In the United States, cancelled physical ballots may be called "spoiled ballots", as distinct from an "invalid vote" which has been cast.
In Canada, a spoiled ballot is one that has been handled by an elector in such a manner that it is ruined beyond use, or that the deputy returning officer finds soiled or improperly printed. The spoilt ballot is not placed in the ballot box, but rather is marked as spoilt by the deputy returning officer and set aside. The elector is given another ballot. A 'rejected ballot' is one which cannot be counted due to improper marking by the voter. Examples of this are ballots which have more than one mark, the intent of the voter cannot be ascertained, or the voter can be identified by their mark.
In many jurisdictions, if multiple elections or referendums are held simultaneously, then there may be separate physical ballots for each, which may be printed on different-colored paper and posted into separate ballot boxes. In the United States, a single physical ballot is often used to record multiple separate votes. In such cases one can distinguish an "invalid ballot", where all votes on the ballot are rendered invalid, from a "partially valid" ballot, with some votes are valid and others invalid.
A voter may deliberately spoil a vote, for example as a protest vote, especially in compulsory voting jurisdictions, to show disapproval of the candidates standing whilst still taking part in the electoral process. Intentionally spoiling someone else's ballot before or during tabulation is an electoral fraud.
The validity of an election may be questioned if there is an unusually high proportion of spoilt votes. In multiple-vote U.S. ballots, "voter roll-off" is calculated by subtracting the number of votes cast for a "down-ballot" office, such as mayor, from the number of votes cast for a "top-of-the-ballot" office, such as president. When the election jurisdiction does not report voter turnout, roll-off can be used as a proxy for residual votes. Some voters may only be interested in voting for the major offices, and not bother filling in the lower positions, resulting in a partially valid ballot.
While it is not illegal to advocate informal voting in Australian federal elections, it was briefly illegal to advise voters to fill out their ballots using duplicated numbers.Albert Langer was jailed for violating an injunction not to advocate incomplete preference voting for the 1996 Australian federal election.
Voter instructions are usually intended to minimize the accidental spoiling of votes. Ballot design can aid or inhibit clarity in an election, resulting in less or more accidental spoiling. Some election officials have discretion to allow ballots where the criteria for acceptability are not strictly met but the voter's intention is clear. More complicated electoral systems may be more prone to errors. Group voting tickets were introduced in Australia owing to the high number of informal votes cast in single transferable vote (STV) elections. When multiple Irish STV elections are simultaneous (as for local and European elections) some voters have marked, say, 1-2-3 on one ballot paper and 4-5-6 on the other; some returning officers consequently allowed 4-5-6 ballots to be counted, until a Supreme Court case in 2015 ruled they were invalid.
The United States Election Assistance Commission's survey of the 2006 midterm elections reported undervoting rate of 0.1% in US Senate elections and 1.6% in US House elections; overvotes were much rarer. Some paper-based voting systems and most DRE voting machines can notify voters of under-votes and over-votes. The Help America Vote Act requires that voters are informed when they have overvoted, unless a paper-ballot voting system is in use.