sumifs based on multiple criteria across multiple sheets

Hi, i have an excel leave tracker where staff forecast their leave. At the back of each month tab (columns AS to BF), i use a countif to check the number of the different types of leave of each staff taken for that month. All these goes into a "Tally" tab where it sums up the number from all the months. The number in the "Tally" tab is then used when the staff calls out the userform and will be able to see at a glance how many days of each type of leave they have taken. After I added all these counting functions, the speed of opening the workbook is dramatically slowed down, probably due to the amount of calculations excel has to do upon opening. What i want to ask is, is there any way to sum up everything in the "Tally" tab without having calculations in the individual month tabs, and in doing so will it speed up the opening process?

I looked up sumifs and countifs, but have no idea how to make it work.

Any help is appreciated.

Example with userform and not vba protected would be a good start

Cheers
Leo