There's been a lot of confusion about who gets free upgrades to Windows 10 on July 29th, but this flowchart should make it nice and simple to determine if you do.
Click the expand button on the graphic for a closer look.
This chart, inspired and expanded upon from this original chart by Amit Agarwal, spells everything out so you know exactly where you stand. If you have a legitimate copy of Windows 7, 8, or 8.1, you're all set to get a free upgrade and you can reserve it now. If you're running the Windows 10 preview, and it was installed over a valid license of Windows 7, 8, or 8.1, you also have access to the free upgrade. If you're running anything older than Windows 7, or installed the Windows 10 preview beta without a previous license, you'll have to fork over the $119 for the standard edition or $199 for the Pro edition. You can, however, continue to use further betas of Windows 10 no matter what.
And if Microsoft changes their mind again, we'll be sure to update this flowchart as soon as possible. [Hat tip to Digital Inspiration]