What an informal vote is
An informal vote is a ballot paper that cannot be included in the count because it does not meet the legal requirements for a formal vote. Informality is about whether the ballot can be interpreted according to the electoral rules; it is not a judgement about the voter's political choice.
Informal ballots are recorded and included in turnout statistics, but they are not credited to a candidate during the distribution of preferences. This is why the informal-vote rate is often reported separately from the formal vote received by parties and candidates.
House and Senate rules are different
The House of Representatives and the Senate use different ballot papers and different preferential systems. A marking pattern that is sufficient for one chamber may not be sufficient for the other. The AEC therefore gives separate instructions for completing each ballot paper.
Voters should follow the instructions printed on the ballot and the current AEC guidance rather than relying on old social-media posts or memories from a previous election. Electoral legislation and ballot formats can change over time.
Common reasons a ballot can be informal
A ballot may be informal if the required sequence of preferences is incomplete, repeated or otherwise incapable of being interpreted under the applicable rules. A completely blank ballot is also informal. Some ballots containing extra marks may still be formal if the voter's intended preferences remain clear and the law permits them to be counted.
Because formality depends on the legal rules and the actual markings, broad claims such as 'any writing makes your vote invalid' are not reliable. Electoral officials assess ballots according to legislation and formal vote-saving provisions.
Informal voting is different from not voting
Australia has compulsory federal voting for enrolled electors, but the legal obligation relates to attending and voting as required by the Electoral Act. An informal ballot and a failure to vote are not the same thing in the election statistics or in the administrative process.
For practical questions about obligations, notices or penalties, the AEC is the authoritative source. This explainer describes the counting concept rather than giving personal legal advice.
How to reduce the risk of an accidental informal vote
Read the instructions on both ballot papers before marking them, use a clear numbering sequence and ask a polling official for a replacement paper if you make a mistake. Polling officials can explain the mechanics of voting without telling a voter which candidate or party to support.
The safest source for current instructions is the AEC. Campaign material from a party can explain that party's recommended preferences, but it should not replace official instructions about what makes a ballot formal.
Primary sources and further reading
We use authoritative Australian institutions as the starting point for this explainer. Follow these links for the underlying rules, official guidance and current details.