One-time Office licences (Home, Home & Business, Professional Plus, Project, Visio) are licensed for one device at a time. "At a time" is the important phrase: when you retire a computer you are allowed to move the licence to its replacement. Here is the sequence that avoids the dreaded "this product key has already been used" message.
Before you touch the new computer
- Sign in to account.microsoft.com/services with the Microsoft account you used when you first activated Office. Your Office product is listed there with an Install button.
- Find your order confirmation e-mail. Even if you never need the key again, the order reference is your proof of purchase.
- On the old computer, open any Office app, go to File → Account and note the product name and the account shown under "Belongs to".
Step 1 — deactivate the old install
For Office 2021 and 2024, deactivation happens from your Microsoft account: on the services page, choose the Office product, then Installs → Deactivate next to the old computer. For Office 2019 the same page applies.
If the old computer is already dead or wiped, skip this — Microsoft treats the licence as moved when you sign in on the new machine, and if activation stalls, the phone activation route (below) sorts it out.
Step 2 — install on the new computer
Download from your Microsoft account rather than a random installer: services page → Install. Run the installer, open Word, and sign in with the same Microsoft account when prompted. In most cases activation completes silently.
Step 3 — if activation asks for a key or fails
- Enter the 25-character key from your order e-mail.
- If you see "This key has already been used", you have not deactivated the old install yet, or Microsoft's systems have not caught up. Try again after an hour, or deactivate from the services page.
- If the error persists, use phone activation: in any Office app, File → Account → Change Product Key, then choose "I want to activate the software by telephone". An automated line gives you a confirmation ID in a few minutes.
Mac specifics
On a Mac, remove Office completely before reinstalling — drag the apps to Trash and delete the licence file (Microsoft publishes a licence-removal tool). Then install from your Microsoft account and sign in.
What does not move
- A licence does not move between platforms: Office for PC stays on PC, Office for Mac stays on Mac. Office 2024 Home and Home & Business keys are issued for either, so if you switch platform you simply install the other version with the same key — but still only on one device at a time.
- A licence bought pre-installed on a PC (OEM) is tied to that PC and does not move. Retail licences, which is what we sell, do.
Stuck halfway through? Our setup guides cover each product step by step, and the support team can walk you through it on the phone.
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