在这个问题上没有很多明确的答案，因为你总是在假设事情。

这个解决方案在两个日期之间进行计算，假设您想保存一个月中的某一天进行比较，(这意味着在计算中考虑了这个月中的某一天)

例如，如果你的日期是2012年1月30日，2012年2月29日就不是一个月，但2013年3月1日就不是一个月。

它经过了相当彻底的测试，可能稍后我们会在使用时清理它，但这里:

private static int TotalMonthDifference(DateTime dtThis, DateTime dtOther)
{
    int intReturn = 0;
    bool sameMonth = false;

    if (dtOther.Date < dtThis.Date) //used for an error catch in program, returns -1
        intReturn--;

    int dayOfMonth = dtThis.Day; //captures the month of day for when it adds a month and doesn't have that many days
    int daysinMonth = 0; //used to caputre how many days are in the month

    while (dtOther.Date > dtThis.Date) //while Other date is still under the other
    {
        dtThis = dtThis.AddMonths(1); //as we loop, we just keep adding a month for testing
        daysinMonth = DateTime.DaysInMonth(dtThis.Year, dtThis.Month); //grabs the days in the current tested month

        if (dtThis.Day != dayOfMonth) //Example 30 Jan 2013 will go to 28 Feb when a month is added, so when it goes to march it will be 28th and not 30th
        {
            if (daysinMonth < dayOfMonth) // uses day in month max if can't set back to day of month
                dtThis.AddDays(daysinMonth - dtThis.Day);
            else
                dtThis.AddDays(dayOfMonth - dtThis.Day);
        }
        if (((dtOther.Year == dtThis.Year) && (dtOther.Month == dtThis.Month))) //If the loop puts it in the same month and year
        {
            if (dtOther.Day >= dayOfMonth) //check to see if it is the same day or later to add one to month
                intReturn++;
            sameMonth = true; //sets this to cancel out of the normal counting of month
        }
        if ((!sameMonth)&&(dtOther.Date > dtThis.Date))//so as long as it didn't reach the same month (or if i started in the same month, one month ahead, add a month)
            intReturn++;
    }
    return intReturn; //return month
}

假设这个月的日期不相关(即2011.1.1和2010.12.31之间的差为1)，date1 > date2为正值，date2 > date1为负值

((date1.Year - date2.Year) * 12) + date1.Month - date2.Month

或者，假设你想要两个日期之间的“平均月”的大致数字，下面的方法应该适用于所有日期，但日期差异非常大。

date1.Subtract(date2).Days / (365.25 / 12)

注意，如果您要使用后一种解决方案，那么您的单元测试应该声明应用程序设计使用的最宽日期范围，并相应地验证计算结果。

更新(感谢Gary)

如果使用“平均月份”方法，“每年平均天数”的更准确数字是365.2425。

除了所有给出的答案，我发现这段代码非常简单。DateTime。MinValue是1/1/1，我们必须从月，年和日减去1。

var timespan = endDate.Subtract(startDate);
var tempdate = DateTime.MinValue + timespan;

var totalMonths = (tempdate.Year - 1) * 12 + tempdate.Month - 1;

var totalDays = tempdate.Day - 1;
if (totalDays > 0)
{
    totalMonths = totalMonths + 1;
}

疯狂的方法，计算所有的日子，超级精确

Helper类:

public class DaysInMonth
{
    public int Days { get; set; }
    public int Month { get; set; }
    public int Year { get; set; }
    public bool Full { get; set; }
}

功能:

    public static List<DaysInMonth> MonthsDelta(DateTime start, DateTime end)
    {
        
        var dates = Enumerable.Range(0, 1 + end.Subtract(start).Days)
          .Select(offset => start.AddDays(offset))
          .ToArray();

        DateTime? prev = null;
        int days = 0;

        List < DaysInMonth > list = new List<DaysInMonth>();

        foreach (DateTime date in dates)
        {
            if (prev != null)
            {
                if(date.Month!=prev.GetValueOrDefault().Month)
                {
                    DaysInMonth daysInMonth = new DaysInMonth();
                    daysInMonth.Days = days;
                    daysInMonth.Month = prev.GetValueOrDefault().Month;
                    daysInMonth.Year = prev.GetValueOrDefault().Year;
                    daysInMonth.Full = DateTime.DaysInMonth(daysInMonth.Year, daysInMonth.Month) == daysInMonth.Days;
                    list.Add(daysInMonth);
                    days = 0;
                }
            }
            days++;
            prev = date;
        }

        //------------------ add last
        if (days > 0)
        {
            DaysInMonth daysInMonth = new DaysInMonth();
            daysInMonth.Days = days;
            daysInMonth.Month = prev.GetValueOrDefault().Month;
            daysInMonth.Year = prev.GetValueOrDefault().Year;
            daysInMonth.Full = DateTime.DaysInMonth(daysInMonth.Year, daysInMonth.Month) == daysInMonth.Days;
            list.Add(daysInMonth);
        }

        return list;
    }

你可以在。net中使用Time Period Library的DateDiff类:

// ----------------------------------------------------------------------
public void DateDiffSample()
{
  DateTime date1 = new DateTime( 2009, 11, 8, 7, 13, 59 );
  DateTime date2 = new DateTime( 2011, 3, 20, 19, 55, 28 );
  DateDiff dateDiff = new DateDiff( date1, date2 );

  // differences
  Console.WriteLine( "DateDiff.Months: {0}", dateDiff.Months );
  // > DateDiff.Months: 16

  // elapsed
  Console.WriteLine( "DateDiff.ElapsedMonths: {0}", dateDiff.ElapsedMonths );
  // > DateDiff.ElapsedMonths: 4

  // description
  Console.WriteLine( "DateDiff.GetDescription(6): {0}", dateDiff.GetDescription( 6 ) );
  // > DateDiff.GetDescription(6): 1 Year 4 Months 12 Days 12 Hours 41 Mins 29 Secs
} // DateDiffSample

下面是一个使用VB的更简洁的解决方案。只适用于年、月、日的净日期。你也可以在c#中加载DateDiff库。

Date1必须<= date2

VB。网

Dim date1 = Now.AddDays(-2000)
Dim date2 = Now
Dim diffYears = DateDiff(DateInterval.Year, date1, date2) - If(date1.DayOfYear > date2.DayOfYear, 1, 0)
Dim diffMonths = DateDiff(DateInterval.Month, date1, date2) - diffYears * 12 - If(date1.Day > date2.Day, 1, 0)
Dim diffDays = If(date2.Day >= date1.Day, date2.Day - date1.Day, date2.Day + (Date.DaysInMonth(date1.Year, date1.Month) - date1.Day))

C#

DateTime date1 = Now.AddDays(-2000);
DateTime date2 = Now;
int diffYears = DateDiff(DateInterval.Year, date1, date2) - date1.DayOfYear > date2.DayOfYear ? 1 : 0;
int diffMonths = DateDiff(DateInterval.Month, date1, date2) - diffYears * 12 - date1.Day > date2.Day ? 1 : 0;
int diffDays = date2.Day >= date1.Day ? date2.Day - date1.Day : date2.Day + (System.DateTime.DaysInMonth(date1.Year, date1.Month) - date1.Day);