I have a task where I need to calculate

• Length
• Active
• Start month
• End month

I take my data from a table that contains periods like this:

• Start date (startdt)
• End date (enddt)

I need to know for a given month

• The length of all current (up to the beginning of current month)
• If beginning of current month is in the middle of the range
• Whether they started in the current month
• Wehther they ended in the previous month

Given month is the beginning of the current month:

To get the length I'm using this formula

if (enddt < month)
    length = startdt.diffInDays(enddt)
else
    if (startdt < month)
        length = startdt.diffInDays(month)

In the range

if (monthOf(startdt) <= monthOf(month) && monthOf(enddt) >= monthOf(month))
    active = true

To dertermine if is the start

if (monthOf(startdt) === monthOf(month) && yearOf(startdt) === yearOf(month))
    start = true

And finally if last day was in previous month

if (monthOf(enddt) === monthOf(lastMonth(month)) && yearOf(lastMonth(month)) > 2016) // everything happens in 2017
    end = true

Everything seems fine, however when I try to sum the numbers they don't add up. If I take active - end it should equal the sum of start, right?