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POCalculate number of fractional month between two dates (C#)
 

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  1. POCalculate number of fractional month between two dates (C#)
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    <p>I would like the number of (potentially fractional) calendar months between two days e.g. 2 Jan 2013 - 15 Feb 2014 should be around 12.5 months.</p> <p>I was surprised not to find this already answered on Google.</p> <p>EDIT: I ended up writing some code - here's my answer if anybody needs the same (my Good Karma for the day :)</p> <pre><code>/// &lt;summary&gt; /// Number of total calendar months between two dates. If day of month is different, /// gives fractional approximation using average days per month. /// &lt;/summary&gt; public static double MonthsBetween(DateTime start, DateTime finish) { //handle if dates switched - calculation same but there's a negative result: double multiplier; if(finish &lt; start) { var temp = start; start = finish; finish = temp; multiplier = -1; } else { multiplier = 1; } //1) 20 Mar 2012 - 13 Jan 2014 --&gt; 2*12 months //2) 15 Jan 2011 - 30 Jul 2012 --&gt; 1*12 months //3) 20 Jan 2010 - 25 Jan 2010 --&gt; 0*12 months double totalMonths = (finish.Year - start.Year)*12; //1) 20 Mar 2012 - 13 Jan 2014 --&gt; 2*12 + 1 - 3 = 22 months //2) 15 Jan 2011 - 30 Jul 2012 --&gt; 1*12 + 7 - 1 = 18 months //3) 20 Jan 2010 - 25 Jan 2010 --&gt; 0*12 + 0 months = 0 months totalMonths += finish.Month - start.Month; ///Now we have "1st of the month to 1st of the month" difference. Days can only be approximated, ///since each month has a different number of days. Statistically (http://en.wikipedia.org/wiki/Month#Julian_and_Gregorian_calendars): const double averageDaysInMonth = 30.436875; ///Remove the days we've included in the starting month (not in actual period): totalMonths -= start.Day / averageDaysInMonth; ///Add the days in the finish month (weren't yet included, since had "1st to 1st"): totalMonths += finish.Day / averageDaysInMonth; //1) 20 Mar 2012 - 13 Jan 2014 --&gt; 2*12 + 1 - 3 - 20/30 + 13/30 = 22 - 7/30 = 21.76 months //2) 15 Jan 2011 - 30 Jul 2012 --&gt; 1*12 + 7 - 1 - 15/30 + 30/30 = 18 + 15/30 = 18.5 months //3) 20 Jan 2010 - 25 Jan 2010 --&gt; 0*12 + 0 - 20/30 + 25/30 = 0 + 5/30 = 0.17 months return totalMonths * multiplier; } </code></pre> <p>Likewise, I realised just after I need something similar for years. Here's that code too, in case it helps somebody:</p> <pre><code>/// &lt;summary&gt; /// Number of total calendar years between two dates. Gives fractional /// approximation if months/days differ. /// &lt;/summary&gt; public static double YearsBetween(DateTime start, DateTime finish) { //handle if dates switched - calculation same but there's a negative result: double multiplier; if (finish &lt; start) { var temp = start; start = finish; finish = temp; multiplier = -1; } else { multiplier = 1; } //1) 20 Mar 2012 - 13 Jan 2014 --&gt; 2 years //2) 15 Jan 2011 - 30 Jul 2012 --&gt; 1 year //3) 20 Jan 2010 - 25 Jan 2010 --&gt; 0 years double totalYears = finish.Year - start.Year; ///Now we have "1st of the year to 1st of the year" difference. Days/months can only be approximated, ///since each year has a different number of days. Statistically (http://en.wikipedia.org/wiki/Year): const double averageDaysPerYear = 365.2425; ///Remove the days we've included in the starting year (not in actual period): totalYears -= start.DayOfYear / averageDaysPerYear; ///Add the days in the finish year (weren't yet included, since had "Jan 1 to Jan 1"): totalYears += finish.DayOfYear / averageDaysPerYear; //1) 20 Mar 2012 - 13 Jan 2014 --&gt; 2 - ~(2*30+20)/365 + 13/365 = 1.82 years //2) 15 Jan 2011 - 30 Jul 2012 --&gt; 1 - 15/365 + ~(6*30+30)/365 = 1.53 years //3) 20 Jan 2010 - 25 Jan 2010 --&gt; 0 - 20/365 + 25/365 = 0.01 years return totalYears * multiplier; } </code></pre>
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    1. USEran Egozi
    1. USalpsystems.com
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      1. POCalculate number of fractional month between two dates (C#)
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    1. COWhat is a definition of '0.5 of the month'? How may days is it?
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      1. POCalculate number of fractional month between two dates (C#)
      1. USJakub Konecki
    2. CO0.5 is good enough for my purposes. I only need a reasonable and consistent fraction in the case of non-round numbers.
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      1. USalpsystems.com
    3. COThe notion of charging fractional months must spring from the mind of somebody that *likes* dealing with never-ending billing disputes. A lawyer perhaps?
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      1. POCalculate number of fractional month between two dates (C#)
      1. USHans Passant
 

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