Apple - Does using a hotspot while connected to wifi use cellular data?

You cannot use your Wi-Fi connection for Internet connectivity while other devices are using Wi-Fi for Personal Hotspot. You can share only a cellular data connection; you cannot share a Wi-Fi connection.

As seen here: http://support.apple.com/kb/ht4517

Yes it does use your data. Even though it says you're connected to wifi the hot spot overrides it & uses your cellular data. I finally figured this out after months of questioning my cellular company as to how it was possible I could use that much data. My son puts it on in the car for his iPad & then when we get out & go inside our home my phone connects to wifi but his iPad still leeches my hot spot from my phone. Of course Rogers couldn't figure that out or at least they didn't want to tell me. It was only after going 4GB over my 10Gb plan & having them cut my data off completely that I was able to figure out what was going on & then called them to confirm. An expensive lesson to learn.