Will I need to pay a Fee to upgrade from W7-Pro to W10?

There seems no time limit or restriction on this provided the license is valid and has not been previously activated.

However upgrading always carries uncertainty and may not succeed. Ensure you have a full disk image before attempting it and make the usual checks and preparations.

Mike Lynch said:

If so, how much?

As long as your installed Window 7 is activated, then it's free to upgrade to Windows 10. Ten Forums has a tutorial that shows how to upgrade from W7 to W10.

Upgrade to Windows 10 from Windows 7 for Free

Mike Lynch said:

If so, how much?

Personally, I would just use the Win 7 product key and do a clean install of Windows 10.
IMO, Win 7 and Win 10 are too un-alike to make an upgrade the best choice.

NavyLCDR said:

Just need to be careful to use the Windows 7 product key from a printed COA label. The actual installed key for Windows 7 may be the factory SLIC key which will not work with Windows 10.

I've never understood the logic behind that.
If MS allows an upgrade from an SLIC key, I can't see why they would disallow a clean install from the same key.

The OP could ofc, do the upgrade, then immediately do a clean install over top of the upgrade.

NavyLCDR said:

Why do you say that? On an upgrade, Windows 10 will assume the Windows 7 license. The Windows 7 license should be activated before upgrading.

- has not been upgraded to Win 10. Sorry if my wording didn't quite suit .

Ghot said:

I've never understood the logic behind that.
If MS allows an upgrade from an SLIC key, I can't see why they would disallow a clean install from the same key.

The OP could ofc, do the upgrade, then immediately do a clean install over top of the upgrade.

A SLIC key allows W7 users to reinstall W7 from a vendor pc disk and activate without needing to contact MS. The key is generic (to each manufacturer). If somebody got hold of the generic key (well known online), they could use it to activate W10 (if it was allowed to activate it) and basically anybody could pirate a clean install.

Allowing an upgrade is ok inasmuch as you are working from an existing activated installation. I guess the upgrader is clever enough to tell of Windows 7 is activated without using SLIC key or COA key.

Some claim they have used COA key on other pcs but that does violate the EULA in most countries. I tried it out of interest and it refused it and returned an obscure error message. So I have no idea if this was just an issue at my end.

I clean installed Win 10 on this machine, but I used a Win 7 Retail key.