Microsoft announced the date in a blog post and at its annual sales meeting Wednesday. The software company had said earlier that Windows 8 would go on sale in October.
Microsoft is releasing the software as a downloadable upgrade that day for PC owners, and letting PC makers start selling computers with Windows 8 the same day.
As an upgrade for users of Windows XP, Vista or 7, Windows will cost $40. That's much less than Microsoft Corp. has charged for previous operating system upgrades. People who bought a Windows 7 computer on June 2 or later can upgrade for $15.