When I think about what you're looking for, I don't think I would use the month-to-date concept alone. If you consider for example that this October there are 5 sundays and last October there were 4 sundays, the business could have increased slightly and still sold less this October compared to last October. At first this sounds like poor analysis, but let's get a little more perspective.
A better analysis could be average sales per day in a month. This is easy to calculate given you only have sales on business days then you would divide total sales of the month so far by a count distinct of the number of days that at least one invoice was registered. In this way you can see if you business is growing regardless of the number of business days in the month. However what if you sell better on Friday's than Monday's and you have more Friday's in a month than Monday's? That doesn't seem like perfect analysis either.
So, we could also break down the average sales per day by each weekday to get an idea if you're selling better on the Friday's of this month compared to the Friday's of the same month last year, but what-if a holiday fell this month on a Friday when last year it fell on a Sunday? That same problem would occur if you base the month-to-date concepto on the same number of business days. So. nothing seems perfect at this point.
There might be more indicators to evaluate a month and I'm not a profesional statistician, but if we put these 3 indications together in the same dashboard, it would give the user a pretty good story about what's happening in the month and along with year-to-date information and his or her gut feeling, the user should have a pretty good idea of how the business is doing.
You make some very good points. Ideally I would want to compare business days completed only. I am not as worried about whether it is a monday or friday. What I would want to know is month to date GP based on business days compared to last years month to date GP based on the same amount of business days. What do you think is the best way to accomplish this?
Qlikview has three built in functions for working day calculations - see a short series on how to use these functions here.
One problem is although these functions allow you to add non-working days (for public holidays), they assume a work week that runs from Monday to Friday, and have no built in way for adding extra working days, so you will have to modify the output to account for your working Saturdays.
My suggestion would be that you add a working days field to you load script that shows (among others):
Working day in month
For non-working days, the working day field could be set to the previous working day, the next working day or zero, depending on your requirements.
Logic will get you from a to b. Imagination will take you everywhere. - A Einstein