For older versions of Windows and Office, Microsoft provides at least five years of mainstream support, followed by another five years of extended support. These life cycles apply equally to business and home versions of Windows and Office.
Generally, "supported" means you have access to at least one type of assisted support option (possibly paid) and no-charge security updates through channels like Windows Update and the Download Center.
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The calculations start with the general availability (GA) date for each product. The official date of retirement for support is the second Tuesday in the first month of the quarter following that anniversary (which also happens to be Patch Tuesday). That grace period typically means a few weeks or months of extra support tacked on at the end of the five- and 10-year support cycles for each product.
The Modern Lifecycle Policy, which applies to Windows 10, Windows 11, and Office 2021, no longer follows that calendar. Instead of mainstream and extended support phases, there's simply a retirement date, with regular updates required to maintain support along the way.
To find the official end-of-support date for any Microsoft product, use the Microsoft Product Lifecycle Search page. When you find the entry for a specific product, you can see the general availability date, the retirement dates for mainstream and extended support, and retirement dates.
Of course, it's worth noting that the end-of-support date is not a death sentence. PCs running Windows XP, Windows Vista, and Windows 7 are still out there, running merrily (if not securely) along. Likewise, PCs running Windows 10 will not stop working when the clock runs out less than three years from now.
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The only difference will be an eerie quiet on the second Tuesday of each month. When the product reaches its retirement date, so do those Patch Tuesday security updates.
Large enterprise customers who have custom support agreements with Microsoft and that are willing to pay a very steep price for a Premium Support agreement have, in the past, been allowed to receive custom updates after the official end of support. The last such support agreement for Windows 2000 ended in 2016, more than six years after extended support officially ended, and some large customers with Windows XP and Windows 7 deployment may still be operating under custom support plans, although Microsoft doesn't publicly acknowledge their existence.
But those options have effectively ended for recent versions of Windows and Office, and even the largest customers are required to pay for Microsoft 365 plans, which can include enterprise licensing, if they expect to receive continuing support.