Looks like VFINX returned 8.8% since 2022-05-01. How did you get to 18%?
https://totalrealreturns.com/n/VFINX,VBMFX,USDOLLAR?start=20...
https://totalrealreturns.com/n/VFINX,VBMFX,USDOLLAR?start=20...
Edit: tweaking your link to May 11 gets it up to 14.8%, and I'm not sure if it's just using the opening price or the lowest of the day