What would be the significance of a legal provision specifying a period of 12 months, rather than 1 year?
<p>Is it just a matter of stylistic aesthetics? Could 12 months realistically ever be taken to mean anything other than what is totally synonymous with a year? The legalistic devil's advocate in me in tempted to look to differences in the numbers of months so that if month were defined as a definite period of say 30 days then you'd potentially end up with periods other than 365 or 366 days as with a year but I ultimately doubt there is any context in which this wouldn't be a pointless tree to bark up.</p>

<blockquote>
<p>Is it just a matter of stylistic aesthetics?</p>
</blockquote>
<p>Yes.</p>
<p>12 months is probably more common in a lease form sometimes used for tenancies of a fixed number of months different from 12. 1 year is probably more common in a lease form sometimes used for multiple years instead of just one, but rarely for part of a year.</p>
<p>This is assuming, of course, that the 12 months are consecutive and not some weird time share.</p>

<p>&quot;Month&quot; is more precise than &quot;year&quot;.</p>
<p>Specifying 12 months frees you from interpretative gray areas about what exactly &quot;one year&quot; means for periods that start in the middle of the calendar year.</p>
<p>Also, while there are <a href="https://en.wikipedia.org/wiki/Month" rel="noreferrer">5 different months</a>, there's <a href="https://en.wikipedia.org/wiki/Year" rel="noreferrer">over a dozen different years</a>. I doubt that there's a serious risk the opposition party would argue that &quot;year&quot; could have meant the Galactic Year or the Lunar Year, but you never know.</p>

<p>Many leases specify that they are for a period of twelve months, but the first month's rent payment will be prorated if the term of occupancy begins on any date other than the first of the month in question.  Thus, if someone is set to occupy a property starting on March 31 for $1,000/month rent plus $1,000 security deposit, the tenant would be required to pay $1,032.26 on before moving in [$967.74 of the first month's rent would be waived for the 30/31 days the property was not occupied], and $1,000 on April 1, and ten more payments of $1,000, and would be expected to move out by the end of February 28, whereupon they would be entitled to receive a refund of $1,000 if they left the apartment in good order.</p>

<p>In most, if not all, countries under <em>secular</em> law, it usually makes very little difference, if any at all, as other answers have explained.</p>
<p>However, under <a href="https://en.wikipedia.org/wiki/Halakha" rel="nofollow noreferrer">Jewish religious law</a>, it makes a <strong>huge</strong> difference.</p>
<p>The Jewish calendar is a combination lunar/solar calendar. There are 12 (regular year) or 13 (leap year) months in each year, with 29 or 30 days in each month. The current fixed calendar (in ancient times the calendar was somewhat dependent on both a judicial review to determine leap years as well as witnesses of the new moon to determine the start of each month) has a cycle of 19 years with 12 regular years and 7 leap years. In addition to leap months, there are adjustments which allow two months to be either 29 or 30 days depending on a number of factors. The reason for these complications is to make sure that <a href="https://en.wikipedia.org/wiki/Passover" rel="nofollow noreferrer">Passover</a> is in the spring season and to make sure that certain holidays do not fall on certain days of the week.</p>
<p>The end result is that in the Jewish calendar there are both religious observances that vary depending on leap years, such as:</p>
<ul>
<li>Bar Mitzvah and Bat Mitzvah (coming of age)</li>
<li>Yahrzeit (anniversary of death)</li>
<li>Regulations relating to mourning for a parent</li>
</ul>
<p>as well as civil effects:</p>
<ul>
<li>Salaries</li>
<li>Rentals</li>
<li>Contracts</li>
</ul>
<p>etc.</p>
<p>These issues have been around &quot;forever&quot; in Jewish law and have been discussed at length in the <a href="https://en.wikipedia.org/wiki/Talmud" rel="nofollow noreferrer">Talmud</a> and in thousands of years of Jewish literature since then. For more specific questions, head on over to <a href="https://judaism.stackexchange.com/">Mi Yodeya</a>.</p>

<p>(As per usual, in the US there are probably tons of local jurisdictions that do things differently, so this is just one common thing...)</p>
<p>In the US, the distinction between felony and misdemeanor charges is commonly the length of the sentence and the cutoff is commonly one year, which can usually be either a felony or misdemeanor sentence. For that reason, maximum misdemeanor sentences may be specified as 12 months and minimum felony sentences may be specified as 1 year, especially since they may be charged under the same law but treated as a different level of offense depending on circumstances (e.g. first offense may be a misdemeanor, subsequent offenses may be felony--but you could tell based on the sentence what level the charge was).</p>
<p>(There was some celebrity back in the 90s or early 2000s who ended up with a jail sentence of 12 months and this difference was a topic that got brought up.)</p>

<p>Some jurisdictions have laws that require certain things to be specified in months rather than years, and failure to specify in the appropriate unit could make the declaration/agreement technically null and void.  I recall observing a hearing where the judge gave a criminal jail sentence noting that &quot;due to quirks of &lt;jurisdiction&gt; law, the sentence must be specified in months&quot; though he also stated the years for easier interpretation.  I don't recall exactly what case or jurisdiction that was, and that line would've been skipped over in any reporting about it just as any other court formality.  I could imagine some quirky laws requiring that certain contracts be specified similarly.</p>

statute-of-limitations time-periods