The legal length of one month
<p>Referring specifically to employment contracts in England, I've seen contracts that specify "one month of notice" to be given before termination of the contract.</p>

<p>This does not specify whether this means one calendar month or a specific number of days/weeks. So, in cases like this, what can be inferred in England?</p>

<blockquote>
  <p>English common law has centuries of experience on this issue, and has developed some settled principles that are applied by the courts.</p>
  
  <ol>
  <li>Prior to 1925, references in contracts to months were interpreted as
  lunar months.  There are 13 lunar months in a year.  By section 61
  of the Law of Property Act 1925, references in contracts to months
  are to be interpreted as calendar months, unless the context
  otherwise requires.</li>
  <li>Calendar months are counted from a specified date. It is not necessary to consider the period from the 1st of a
  month to, say, 31st (unless the notice period starts on 1st of a
  month).  This contrasts with the usual understanding of calendar
  year, which tends to be thought of as the period from 1st January to
  31st December.</li>
  <li>The “corresponding date rule” requires that one looks
  at the same date in the diary the relevant number of months ahead. 
  Thus a period of 3 months from 20th April expires on 20th July.  In
  the case of Dodds v Walker [1980] 1 WLR 1061, in the Court of
  Appeal, Templeman LJ said:</li>
  </ol>
  
  <p><em>"…if an act is authorised to be performed on any arbitrary day in any month of the year, then one month elapses on the corresponding day of the next month, provided that the day of the act itself is excluded from computation."</em></p>
  
  <p>In the same case, in the House of Lords, Lord Diplock said:</p>
  
  <p><em>"The corresponding date rule is simple.  It is easy of application.  …all that the calculator has to do is make in his diary the corresponding date in the appropriate subsequent month."</em></p>
  
  <p>In the same case, Templeman LJ clarified that if the period expired on a date that did not exist in a particular month (eg 31st February), then the period would expire on the last day of that month.</p>
  
  <p><a href="https://ipdraughts.wordpress.com/2012/04/20/invalid-notices-of-termination-calculation-of-time-periods/" rel="noreferrer">Source</a></p>
</blockquote>

<p>See also the <a href="http://www.legislation.gov.uk/ukpga/1996/18/section/210" rel="noreferrer">Employment Law Act 1996</a>, which discusses statutory notice periods specifically, and in particular, s.210:</p>
<blockquote>
<p>(2) In any provision of this Act which refers to a period of continuous employment expressed in months or years—</p>
<p>(a) a month means a calendar month</p>
</blockquote>
<p>On this basis, as well as dw's answer about the Common Law, one month's notice refers to a calendar month.</p>

contract-law england-and-wales employment