How is subscription upgrade pro-rate amount calculated?

[Dazz]

I have a member that purchased one of the tiers ($25)of subscriptions on my site on 7/2022 and expires 7/2023. They are wanting to upgrade to a higher tier ($60). The system is trying to collect quite a bit higher than it should for the rest of the year ($50.14).  Since they are half way through their initial year subscription; I'd expect it to be around $30 for the difference in upgrade costs. 

Why is this calculating the pro-rate like this?

[Marc]

I think the confusion here is you are looking at a calendar year. Thats incorrect. What its doing is charging for a year, starting today, then taking off what they have already paid for the month, minus what they already used for this month. So it would indeed be almost a full year. 

[Dazz]

Thanks Marc.  I think that explains it!