How to Calculate monthly Values in a daily view?

My shop takes Credit Card payments and the % fees depend on monthly sales volumes.

I have built a KPI Sheet, which gives me the cost per transaction including the credit card fees.

What I would like to do is the following:

calculate the fixed Volume for any given month which is then used to calculate the percentage Fees.

I am already doing this in a monthly view where I basically calculate the days completed in that month, and then extrapolate my numbers for the full month. i.e. on day 15 in a 30 day month, I would calculate "current volume x 2" for the full month.

Once I switch to Daily or Weekly, those volumes don't work anymore, because I keep multiplying the period's volume by 2, Instead of taking the total volume of 15 days again...

Here are the forumlas I am using:

To calculate the days in any full month:

AVG(DAY(DATEADD('day',-1,DATEADD('month',1,DATETRUNC('month',[created])))))

To calculate the days completed in a given month:

If MONTH([created]) = MONTH(TODAY()) AND YEAR([created]) = YEAR(TODAY()) THEN DAY(TODAY()-1)

ELSE 

DAY(DATEADD('day',-1,DATEADD('month',1,DATETRUNC('month',[created])))) 

END

Calculate the multiplier of the actual volume:

1/(AVG([Days Completed in given Month])/[Days in full Month])

To calculate the full month applicable Orders

[Sales]* [Full Month Multiplier]

How do I "not" calculate that Sales Volume for the selected period but for the days completed in the respective month?