title: AddDays() is not incrementing month
body: <p>In my code <code>AddDays(1)</code> is working correctly for all days except the last day of the month.</p>
  
  <p>I have a datatable containing data read in from a csv. Each row contains a date as string in format <code>yyyy-mm-dd</code>. I want to add a day this date.
  The code below is working for all dates where the day is not the last day of the month, but fails to increment the month otherwise.</p>
  
  <p>Example: </p>
  
  <p><code>2019-07-30</code> correctly increments to <code>2019-07-31</code>, but <code>2019-07-31</code> increments to <code>2019-07-01</code> rather than to <code>2019-08-01</code>.</p>
  
  <p>I've tried <code>Date.Parse</code>, and tried using <code>System.Globalization.CultureInfo.InvariantCulture</code> or <code>System.Globalization.DateTimeFormatInfo.InvariantInfo</code> without success.</p>
  
  <p>MS documentation says </p>
  
  <blockquote>
    <p>The AddDays method takes into account leap years and the number of days in a month when performing date arithmetic.</p>
  </blockquote>
  
  <p>What am I doing wrong?</p>
  
  <pre><code>Dim enUK As New System.Globalization.CultureInfo("en-UK")
  For Each row As DataRow In Outs.Select
     Dim Lastdate As Date = DateTime.ParseExact(row("EndDate"), "yyyy-mm-dd", enUK) 
     Dim DepDate As Date = Lastdate.AddDays(1)
     row("Date") = DepDate.ToString("yyyy-mm-dd")
  Next
  </code></pre>
  
  <p>I expect the value of <code>row("Date")</code> to be <code>2019-08-01</code> for a <code>row("EndDate")</code> value of <code>2019-07-31</code>, rather than the value I'm getting of <code>2019-07-01</code>.</p>