Without much data, difficult to answer without assumptions, but her
goes...
Assuming each sheet is named bu month and you want to sum the same cel
(let's say B5) in all tabs, Insert a new tab at the end, named Yea
summary.
In Cell B5, on the Year summary, your formula would b
=sum(Jan

ec!B5)
This will of course only work if your furthest left tab is named Ja
and your second last to the right is named Dec with the Year Summar
being farthest rught.
Let me know if this works for you or provide more information regardin
how sheets are set up