Help My Fat Arms

[KnitKnot]

Hi everyone, long time since I've been here but I've kept knitting and haven't forgotten all the help I've received here and used well. Thank you.
Now about my fat arms....
I just finished a pullover in chunky Denim Ultra and after sewing in one of the arms I suddenly thought "good grief that armhole looks small".
Boo hoo! The sweater is a deliberate size up for me so is a kind of slopppy joe, so I thought for sure the arms would be roomy, but although I kept the right guage the armholes are just too small - I'd say a good inch to inch & 1/2. I know I'll have to take it apart and rework it. Big sighs.....
The big question is, how can I avoid it in the future. I can't find any advice on how to recalculate increases to take me to the sleeve top and corresponding along the body of the sweater to end up with the added inches needed.
Has anyone encountered this problem and found a way to do it without a maths degree?
Please help the sad chubby armed knitter?