YOY
From ACT Wiki
Year On Year, particularly in the context of percentage growth.
For example if revenues have grown as follows:
Year 1: $100m
Year 2: $110m
Year 3: $132m
The related year-on-year (YOY) percentage growth figures are calculated as:
Years 1-2: [110-100=10]/100 - 1 = 10%
Years 2-3: [132-110=22]/110 = 20%.
Also known as Y/Y.