我对两个日期之间总月差的理解有一个整数部分和一个小数部分(日期很重要)。

积分部分是整个月的差额。

对我来说，小数部分是开始月份和结束月份之间一天的百分比(到一个月的全部天数)的差值。

public static class DateTimeExtensions
{
    public static double TotalMonthsDifference(this DateTime from, DateTime to)
    {
        //Compute full months difference between dates
        var fullMonthsDiff = (to.Year - from.Year)*12 + to.Month - from.Month;

        //Compute difference between the % of day to full days of each month
        var fractionMonthsDiff = ((double)(to.Day-1) / (DateTime.DaysInMonth(to.Year, to.Month)-1)) -
            ((double)(from.Day-1)/ (DateTime.DaysInMonth(from.Year, from.Month)-1));

        return fullMonthsDiff + fractionMonthsDiff;
    }
}

有了这个扩展，这些是结果:

2/29/2000 TotalMonthsDifference 2/28/2001 => 12
2/28/2000 TotalMonthsDifference 2/28/2001 => 12.035714285714286
01/01/2000 TotalMonthsDifference 01/16/2000 => 0.5
01/31/2000 TotalMonthsDifference 01/01/2000 => -1.0
01/31/2000 TotalMonthsDifference 02/29/2000 => 1.0
01/31/2000 TotalMonthsDifference 02/28/2000 => 0.9642857142857143
01/31/2001 TotalMonthsDifference 02/28/2001 => 1.0

我写了一个函数来完成这个，因为其他的方法都不适合我。

public string getEndDate (DateTime startDate,decimal monthCount)
{
    int y = startDate.Year;
    int m = startDate.Month;

    for (decimal  i = monthCount; i > 1; i--)
    {
        m++;
        if (m == 12)
        { y++;
            m = 1;
        }
    }
    return string.Format("{0}-{1}-{2}", y.ToString(), m.ToString(), startDate.Day.ToString());
}

扩展的Kirks结构与ToString(格式)和持续时间(长ms)

 public struct DateTimeSpan
{
    private readonly int years;
    private readonly int months;
    private readonly int days;
    private readonly int hours;
    private readonly int minutes;
    private readonly int seconds;
    private readonly int milliseconds;

    public DateTimeSpan(int years, int months, int days, int hours, int minutes, int seconds, int milliseconds)
    {
        this.years = years;
        this.months = months;
        this.days = days;
        this.hours = hours;
        this.minutes = minutes;
        this.seconds = seconds;
        this.milliseconds = milliseconds;
    }

    public int Years { get { return years; } }
    public int Months { get { return months; } }
    public int Days { get { return days; } }
    public int Hours { get { return hours; } }
    public int Minutes { get { return minutes; } }
    public int Seconds { get { return seconds; } }
    public int Milliseconds { get { return milliseconds; } }

    enum Phase { Years, Months, Days, Done }


    public string ToString(string format)
    {
        format = format.Replace("YYYY", Years.ToString());
        format = format.Replace("MM", Months.ToString());
        format = format.Replace("DD", Days.ToString());
        format = format.Replace("hh", Hours.ToString());
        format = format.Replace("mm", Minutes.ToString());
        format = format.Replace("ss", Seconds.ToString());
        format = format.Replace("ms", Milliseconds.ToString());
        return format;
    }


    public static DateTimeSpan Duration(long ms)
    {
        DateTime dt = new DateTime();
        return CompareDates(dt, dt.AddMilliseconds(ms));
    }


    public static DateTimeSpan CompareDates(DateTime date1, DateTime date2)
    {
        if (date2 < date1)
        {
            var sub = date1;
            date1 = date2;
            date2 = sub;
        }

        DateTime current = date1;
        int years = 0;
        int months = 0;
        int days = 0;

        Phase phase = Phase.Years;
        DateTimeSpan span = new DateTimeSpan();

        while (phase != Phase.Done)
        {
            switch (phase)
            {
                case Phase.Years:
                    if (current.AddYears(years + 1) > date2)
                    {
                        phase = Phase.Months;
                        current = current.AddYears(years);
                    }
                    else
                    {
                        years++;
                    }
                    break;
                case Phase.Months:
                    if (current.AddMonths(months + 1) > date2)
                    {
                        phase = Phase.Days;
                        current = current.AddMonths(months);
                    }
                    else
                    {
                        months++;
                    }
                    break;
                case Phase.Days:
                    if (current.AddDays(days + 1) > date2)
                    {
                        current = current.AddDays(days);
                        var timespan = date2 - current;
                        span = new DateTimeSpan(years, months, days, timespan.Hours, timespan.Minutes, timespan.Seconds, timespan.Milliseconds);
                        phase = Phase.Done;
                    }
                    else
                    {
                        days++;
                    }
                    break;
            }
        }

        return span;
    }
}

这个简单的静态函数计算两个Datetimes之间的月份分数。

1.1. 到31.1。= 1.0 1.4. 到15.4。= 0.5 16.4. 到30.4。= 0.5 1.3. 到1.4。= 1 + 1/30

该函数假设第一个日期比第二个日期小。要处理负时间间隔，可以通过在开始时引入符号和变量交换来轻松地修改函数。

public static double GetDeltaMonths(DateTime t0, DateTime t1)
{
     DateTime t = t0;
     double months = 0;
     while(t<=t1)
     {
         int daysInMonth = DateTime.DaysInMonth(t.Year, t.Month);
         DateTime endOfMonth = new DateTime(t.Year, t.Month, daysInMonth);
         int cutDay = endOfMonth <= t1 ? daysInMonth : t1.Day;
         months += (cutDay - t.Day + 1) / (double) daysInMonth;
         t = new DateTime(t.Year, t.Month, 1).AddMonths(1);
     }
     return Math.Round(months,2);
 }

简单快速的解决方案，计算2个日期之间的总月份。 如果你只想得到不同的月份，而不计算From date中的月份-只需从代码中删除+1。

public static int GetTotalMonths(DateTime From, DateTime Till)
        {
            int MonthDiff = 0;

            for (int i = 0; i < 12; i++)
            {
                if (From.AddMonths(i).Month == Till.Month)
                {
                    MonthDiff = i + 1;
                    break;
                }
            }

            return MonthDiff;
        }

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。