The only caveat is that anything higher than 36 months will be lost.

As you join the Game Pass Ultimate service, the process will allow you to convert the time left to the new service up to 36 months. If you are a new Game Pass customer, you can add three years of prepaid Xbox Live Gold (which you can usually find online for $60 or sometimes even for $50). How Xbox Live Gold to Game Pass Ultimate works

How to convert Xbox Live Gold to Game Pass Ultimate.How Xbox Live Gold to Game Pass Ultimate works.Microsoft’s Xbox Game Pass is a subscription service that gives you unlimited access to download and play over 100 high-quality games using the Xbox Live network on Xbox One, Xbox Series X and S, or PC. This is possible because Microsoft wants to lure users to the service, so the company has a promotion that allows you to bring any prepaid time you have left on Xbox Live Gold to the Game Pass service at the same rate. The Xbox Game Pass Ultimate subscription costs $15 every month, but there is a trick you can use to get up to 36 months for only $180 (or even less), bringing the cost down to $5 per month.

Xbox game pass ultimate 3 months deal