Don’t forget the Office estate nobody has audited since 2021

On 13 October 2026, Office LTSC 2021 and the perpetual Office 2021 apps stop getting security updates for good. The migration is the easy part. The problem is that most firms cannot tell you how many of those installs are still running, or where.

Who this is for

• IT managers who bought Office 2021 volume licences in 2021 and never tracked where they landed.
• Ops teams still running Office LTSC on air-gapped, kiosk, lab or shared-workstation machines.
• Anyone who inherited an estate through an acquisition and has no clean device inventory.
• Finance leads who assume “we moved everyone to Microsoft 365” is actually true.

What’s happening on 13 October 2026

Office 2021 is a fixed-lifecycle product. It never had the long mainstream-plus-extended runway that older Office versions enjoyed. Both the volume-licensed Office LTSC 2021 and the retail perpetual Office 2021 apps reach end of support on 13 October 2026. After that date Microsoft ships no more security updates, no bug fixes, no technical assistance. The applications keep opening, which is exactly why this one is dangerous: nothing breaks, so nobody notices.

This is not the same event as the Windows 10 end of support you have already been reading about. It is a separate lifecycle, on a machine you may have long since stopped thinking about.

Why it bites

Outlook, Word and Excel are among the most heavily targeted attack surfaces in any organisation, because they open files that arrive from outside. An unpatched Office install is a document-parsing vulnerability waiting for the next crafted attachment. Once the updates stop, every new CVE in that codebase stays open on your estate permanently.

The compounding problem is visibility. Perpetual Office tends to survive in exactly the places your management tooling does not reach: the reception PC, the meeting-room machine, the finance workstation that was excluded from the last rollout “because it runs that one add-in”, the developer laptop rebuilt from an old image. If your asset register cannot answer “how many Office 2021 installs do we have and on which devices”, the deadline is not really your problem. The blind spot is. This is the same gap I keep writing about in the context of asset registers that describe what should exist rather than what does — see ISO 15926 gives you a vocabulary, almost nobody has built the register.

The one thing to do before October

Run one query, today: pull every device with an Office click-to-run or MSI install and filter to product version 16.0 builds licensed as 2021 or LTSC 2021. Do it from your endpoint management or inventory tooling, not from a spreadsheet somebody maintained by hand. The output is your migration scope. Everything that does not appear in that query is a device you have lost track of, which is the finding that actually matters.

You have until 13 October 2026 to move those installs to Microsoft 365 Apps, Office LTSC 2024, or off Office entirely. Nine months is enough time to do it calmly. It is not enough time to first discover you have twice as many installs as you thought.

If the count comes back larger than you expected and you do not have the hands to remediate it before the date, that is a capacity problem, not a strategy problem. My sister-brand delivery team does exactly this — inventory sweep, migration packaging and rollout — as a fixed-scope build. See how I work, and bring me the device count you cannot close by October.

Engagements are scoped and priced up front, no open-ended retainers. The date is 13 October 2026.