 <p>A very crude way of doing it would be, simply subtracting the registration date from the current time, and get the total months from the number of days:</p> <pre><code>TimeSpan age = DateTime.Now - registrationDate; int months = (int) (age.TotalDays/30); </code></pre> <p>After a few years (about six or seven) you'll get extra months counted. Counting in months is not easy because a month is not an exact quantity. I'm guessing that a vehicle being six years old is probably very common, so this may not be a good fit.</p> <p>A better alternative would be to subtract the years and the months directly:</p> <pre><code>int fullYears = (now.Year - registrationDate.Year) * 12; int partialYear = now.Month - registrationDate.Month; int months = fullYears + partialYear; </code></pre>