Transfer GP Ultimate membership

this should answer you're question

"All conversions to Xbox Game Pass Ultimate are final: Once converted, you cannot re-convert your Xbox Game Pass Ultimate membership back to a previous membership."

This statement covers ONLY the conversion of currently stacked memberships; that is, memberships that are active or prepaid subscriptions that are currently redeemed. With the conversion, all those memberships become Game Pass Ultimate, and will
run until the end of that subscription period. So, let's say you have 12 months of Gold that expire on 1 July 2019. If you do the conversion, your renewal date moves to 1 August 2019, as you get the first month of GP Ultimate for $1, then your existing 12
months will become GP Ultimate.

Translation:

I have Xbox Live Gold payment for 12 months, how can I go to ultimate?

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Answer:

Hi, you can upgrade to Gamepass Ultimate if you have other subscription simply by purchasing one (or more) month of Gamepass Ultimate.

If this is the first time that you try GP Ultimate your active subscription will be added to the purchased months of GP Ultimate (ie. if you have 12 months of gold and you buy 1 months of GP Ultimate you will have
13 months of GP Ultimate)

if this is not the first time that you upgrade to Ultimate your active subscription will be combined with a fixed ratio (ie. if you have 12 months of gold and you buy 1 months of GP Ultimate you will have
5 months of GP Ultimate, since 12 months of gold correspond to 4 of GP Ultimate)

More information about GP Ultimate upgrade here: https://www.xbox.com/es-es/xbox-game-pass?source=lp

Yes it is allowed. You can still do the conversion on your first account as well, but that account would not be eligible for the promotional price since it has already had Ultimate.

@Gaelunafn - That conversion only applies if you are adding a prepaid Gold or Game Pass card while you have an active Game Pass Ultimate subscription. If you only gave standard Gold or Game Pass and are purchasing Game Pass Ultimate, it will upgrade at a
ratio of 1:1 regardless of if you have previously had Game Pass Ultimate or not.

But if you do the whole process on a new account, a second account, is it allowed?

Hello,

after the first time you couldn‘t use the conversion of this kind again. It is not possible to buy it again for 1 Euro. If you buy as example 12 months of Gold and buy 1 month of Ultimate the 12 months convert into 4 months of Ultimate. Down in this Link in
the FAQ section is a conversion table with further information about conversion.