The Interpretation Act 1957 applies to the interpretation of all laws, so it is a useful act to know.

The act was last amended to incorporate the 1993 Interim Constitution. While there are some archaic and strange provisions, like the mention of the former colonies and the Royal Letters Patent of His Majesty King William the Fourth of 1832, most of the act is still highly relevant.

Here are some things to know:

When interpreting any definition

  • ‘Month’ means a calendar month. In the absence of any clear indication to the contrary to be found in the words used in any particular legislation a calendar month running from an arbitrary date expires with the day in the succeeding month immediately preceding the day corresponding to the date upon which the period starts. Thus, if a calendar month commences on the 10th of one month it will expire at the end of the 9th day of the succeeding month.
  • The word ‘person’ includes councils, companies and any body of persons corporate or unincorporated.
  • With good foresight, the act says that ‘writing’ includes typewriting, photography and all other modes of representing or reproducing words in visible form.
  • When any particular number of days is prescribed in an act, you must exclude the first and include the last day, unless the last day happens to fall on a Sunday or on any public holiday, in which case the Sunday or public holiday is also excluded.
  • The act was drafted before the days of gender neutrality, and says that words importing the masculine gender include females.

Service of documents by post

There is often confusion around service of documents by post. Some acts like the National Credit Act have specific requirements. However, in other cases, where a law requires any document to be served by post then, unless the contrary intention appears, service is deemed to be effected by properly sending a registered letter. And unless the contrary is proved, service is effected at the time at which the letter would be delivered in the ordinary course of post.


The Interpretation Act applies to statutes, and not to contracts. The common law applies to the interpretation of contracts, unless a contract specifically imports the provisions of the Interpretation Act (which is unlikely).