在我的情况下，需要计算从开始日期到下个月这一天的前一天或从月初到月底的完整月份。

例如:从1/1/2018到31/1/2018是一个完整的月 例2:从5/1/2018到4/2/2018是一个完整的月

基于此，我的解决方案如下:

public static DateTime GetMonthEnd(DateTime StartDate, int MonthsCount = 1)
{
    return StartDate.AddMonths(MonthsCount).AddDays(-1);
}
public static Tuple<int, int> CalcPeriod(DateTime StartDate, DateTime EndDate)
{
    int MonthsCount = 0;
    Tuple<int, int> Period;
    while (true)
    {
        if (GetMonthEnd(StartDate) > EndDate)
            break;
        else
        {
            MonthsCount += 1;
            StartDate = StartDate.AddMonths(1);
        }
    }
    int RemainingDays = (EndDate - StartDate).Days + 1;
    Period = new Tuple<int, int>(MonthsCount, RemainingDays);
    return Period;
}

用法:

Tuple<int, int> Period = CalcPeriod(FromDate, ToDate);

注意:在我的情况下，需要计算完整月份之后的剩余天数，所以如果不是你的情况，你可以忽略天数结果，甚至可以将方法返回值从元组更改为整数。

如果您想要完整月份的确切数目，总是正的(2000-01-15,2000-02-14返回0)，则考虑完整月份是当您到达下个月的同一天时(类似于年龄计算)

public static int GetMonthsBetween(DateTime from, DateTime to)
{
    if (from > to) return GetMonthsBetween(to, from);

    var monthDiff = Math.Abs((to.Year * 12 + (to.Month - 1)) - (from.Year * 12 + (from.Month - 1)));

    if (from.AddMonths(monthDiff) > to || to.Day < from.Day)
    {
        return monthDiff - 1;
    }
    else
    {
        return monthDiff;
    }
}

编辑原因:旧代码在某些情况下不正确，如:

new { From = new DateTime(1900, 8, 31), To = new DateTime(1901, 8, 30), Result = 11 },

Test cases I used to test the function:

var tests = new[]
{
    new { From = new DateTime(1900, 1, 1), To = new DateTime(1900, 1, 1), Result = 0 },
    new { From = new DateTime(1900, 1, 1), To = new DateTime(1900, 1, 2), Result = 0 },
    new { From = new DateTime(1900, 1, 2), To = new DateTime(1900, 1, 1), Result = 0 },
    new { From = new DateTime(1900, 1, 1), To = new DateTime(1900, 2, 1), Result = 1 },
    new { From = new DateTime(1900, 2, 1), To = new DateTime(1900, 1, 1), Result = 1 },
    new { From = new DateTime(1900, 1, 31), To = new DateTime(1900, 2, 1), Result = 0 },
    new { From = new DateTime(1900, 8, 31), To = new DateTime(1900, 9, 30), Result = 0 },
    new { From = new DateTime(1900, 8, 31), To = new DateTime(1900, 10, 1), Result = 1 },
    new { From = new DateTime(1900, 1, 1), To = new DateTime(1901, 1, 1), Result = 12 },
    new { From = new DateTime(1900, 1, 1), To = new DateTime(1911, 1, 1), Result = 132 },
    new { From = new DateTime(1900, 8, 31), To = new DateTime(1901, 8, 30), Result = 11 },
};

我在VB中检查了这个方法的用法。NET通过MSDN，它似乎有很多用途。c#中没有这样的内置方法。(即使这不是一个好主意)你可以在c#中调用VB。

将Microsoft.VisualBasic.dll添加到 你的项目作为参考 使用 Microsoft.VisualBasic.DateAndTime.DateDiff 在代码中

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void button1_Click(object sender, EventArgs e)
    {

        label3.Text = new DateDifference(Convert.ToDateTime("2018-09-13"), Convert.ToDateTime("2018-11-15")).ToString();
        label2.Text = new DateDifference(Convert.ToDateTime("2018-10-12"), Convert.ToDateTime("2018-11-15")).ToString();

        DateDifference oDateDifference = new DateDifference(Convert.ToDateTime("2018-11-12"));
       label1.Text  =   oDateDifference.ToString();

    }
}




public class DateDifference
{
    public DateTime start { get; set; }
    public DateTime currentDAte { get; set; }
    public DateTime origstart { get; set; }
    public DateTime origCurrentDAte { get; set; }

    int days { get; set; }
    int months { get; set; }
    int years { get; set; }

    public DateDifference(DateTime postedDate, DateTime currentDAte)
    {
        this.start = this.removeTime(postedDate);
        this.currentDAte = this.removeTime(currentDAte);
        this.origstart = postedDate;
        this.origCurrentDAte = currentDAte;

    }

    public DateDifference(DateTime postedDate)
    {
        DateTime currentDate_ = DateTime.Now;
        this.start = this.removeTime(postedDate);
        this.currentDAte = this.removeTime(currentDate_);
        this.origstart = postedDate;
        this.origCurrentDAte = currentDate_;
        if (start > this.currentDAte)
        {
            throw new Exception("Current date is greater than date posted");
        }
        this.compute();
    }

    void compute()
    {
        while (this.start.Year <= this.currentDAte.Year)
        {
            if (this.start.Year <= this.currentDAte.Year && (this.start.AddMonths(1) <= this.currentDAte))
            {
                ++this.months;
                this.start = this.start.AddMonths(1);
            }

            if ((this.start.Year == this.currentDAte.Year) && (this.start >= this.currentDAte.AddMonths(-1) && this.start <= this.currentDAte))
            {
                break;
            }
        }

        while (this.start.DayOfYear < this.currentDAte.DayOfYear)
        {
            ++this.days;
            this.start = start.AddDays(1);
        }

        if (this.months > 11)
        {
            while (this.months > 11)
            {
                ++this.years;
                this.months = months - 12;
            }
        }

    }


    public override string ToString()
    {
        if (this.start > this.currentDAte)
        {
            throw new Exception("Current date is greater than date posted");
        }
        String ret = this.ComposeTostring();
        this.reset();
        return ret;
    }

    private String ComposeTostring()
    {
        this.compute();
        if (this.years > 0)
        {
            if (this.months > 0)
            {
                if (this.days > 0)
                {
                    return String.Format("{0} year{1}, {2} month{3} && {4} Day{5} ago", this.years, plural(this.years), this.months, plural(this.months), this.days, plural(this.days));
                }
                return String.Format("{0} year{1}, {2} month{3} ago", this.years, plural(this.years), this.months, plural(this.months));
            }
            else
            {
                if (this.days > 0)
                {
                    return String.Format("{0} year{1},{2} day{3} ago", this.years, plural(this.years), this.days, plural(this.days));
                }

                return String.Format("{0} year{1} ago", this.years, plural(this.years));

            }
        }

        if (this.months > 0)
        {
            if (this.days > 0)
            {
                return String.Format("{0} month{1}, {2} day{3} ago", this.months, plural(this.months), this.days, plural(this.days));
            }
            else
            {
                return String.Format("{0} month{1} ago", this.months, plural(this.months));
            }
        }

        if ((this.origCurrentDAte - this.origstart).Days > 0)
        {
            int daysDiff = (this.origCurrentDAte - this.origstart).Days;
            this.origstart = this.origstart.AddDays(daysDiff);
            int HoursDiff = (this.origCurrentDAte - this.origstart).Hours;
            return String.Format("{0} day{1}, {2} hour{3} ago", daysDiff, plural(daysDiff), HoursDiff, plural(HoursDiff));

        }
        else if ((this.origCurrentDAte - this.origstart).Hours > 0)
        {
            int HoursDiff = (this.origCurrentDAte - this.origstart).Hours;
            this.origstart = this.origstart.AddHours(HoursDiff);
            int MinDiff = (this.origCurrentDAte - this.origstart).Minutes;
            return String.Format("{0} hour{1}, {2} minute{3} ago", HoursDiff, plural(HoursDiff), MinDiff, plural(MinDiff));
        }
        else if ((this.origCurrentDAte - this.origstart).Minutes > 0)
        {

            int MinDiff = (this.origCurrentDAte - this.origstart).Minutes;
            this.origstart = this.origstart.AddMinutes(MinDiff);
            int SecDiff = (this.origCurrentDAte - this.origstart).Seconds;
            return String.Format("{0} minute{1}, {2} second{3} ago", MinDiff, plural(MinDiff), SecDiff, plural(SecDiff));
        }
        else if ((this.origCurrentDAte - this.origstart).Seconds > 0)
        {
            int sec = (this.origCurrentDAte - this.origstart).Seconds;
            return String.Format("{0} second{1}", sec, plural(sec));
        }

        return "";
    }

    String plural(int val)
    {
        return (val > 1 ? "s" : String.Empty);
    }

    DateTime removeTime(DateTime dtime)
    {
        dtime = dtime.AddHours(-dtime.Hour);
        dtime = dtime.AddMinutes(-dtime.Minute);
        dtime = dtime.AddSeconds(-dtime.Second);
        return dtime;
    }

    public void reset()
    {

        this.days = 0;
        this.months = 0;
        this.years = 0;
        this.start = DateTime.MinValue;
        this.currentDAte = DateTime.MinValue;
        this.origstart = DateTime.MinValue;
        this.origCurrentDAte = DateTime.MinValue;
    }
}

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;
}

  var dt1 = (DateTime.Now.Year * 12) + DateTime.Now.Month;
  var dt2 = (DateTime.Now.AddMonths(-13).Year * 12) + DateTime.Now.AddMonths(-13).Month;
  Console.WriteLine(dt1);
  Console.WriteLine(dt2);
  Console.WriteLine((dt1 - dt2));