Adjusted R2 formula in Analysis Toolpak

I'm switching over a spreadsheet from using the ATP to using LINEST. Because LINEST doesn't calculate an adjusted R2, my thought was I could just do it manually based on the R2 value LINEST calculates. 

However, the Toolpak Adjusted R2 value does not come out the same as any Adjusted R2 formula I can find. Currently using the formulas as seen here  but the values I'm getting are waay off. I've checked my formula with known values so I know it's OK -I'm beginning to thing the Toolpak calculates adjusted R2 differently than the generally accepted methods I've found online. I am forcing the intercept to zero, which I know has caused problems in past versions but I'm using 2016. Any help would be much appreciated!