I am considering applying for US PhD Program. In the UK, at many unis the first year does not count towards degree classification. Is this known in the US? Will they be wondering why I stated I have X %, but they calculate Y % ? Shall I explain to grad school admissions that 'the first year didn't count' towards my degree classification?
For the benefit of non UK members, the first year marks of a degree at a UK university is not used for calculating a student's final grade. The only requirement to continue on the degree is achieve at least 40%. It is therefore not uncommon for students to achieve marks in their first year which do not reflect their full abilities, and while it does not affect their grades it can affect how future employer or post graduate admissions view their application!
If this is the case you should address this in your personal statement. Tell them how you gained a new perspective and work ethic after your first year at university and demonstrate this with your improved results in your subsequent years along with appropriate participation in university clubs and societies.
If however your first year marks are consistent with your subsequent years, there is no need to mention it. Your application is about you as a potential student, not about explaining the intricacies of UK grade calculations.
Edit: The reasoning behind only requiring a mark of 40% for the first year is to allow students some adjustment to a more independent study style and also to give young adults entering university the freedom to have new life experiences outside of academia. The prevalent philosophy at UK institutions is that academic achievement is not the only goal of attending university (though it is obviously still important!)
Since the progression of students enrolled on a degree is decided on a department by department basis its impossible to find a single decree stating this how all UK universities operate it is by far how the majority work. Provided below are links to progression guidance from 2 UK universities, stating that only pass marks (40%) are required and that this mark will not be used to calculate degree classifications. University of York Progression, University of Durham Progression
I've served on a PhD admissions committee as a student member, and we considered many different kinds of extenuating factors that might explain low GPA. That committee would certainly have appreciated the info. I would mention it, being careful to frame it in a way that portrays myself as a successful future researcher.
The concern of a PhD admissions committee is primarily, "Will this individual successfully complete our program?" and secondary, "Will they be a leader in their field of research after completing our program?" What you do not want to do is imply that you blew off the entire year because you didn't have grades to motivate you. No grad school wants someone who's primarily motivated by grades. Even if your PhD program puts emphasis on grades in the program (mine doesn't, but I think the more STEM fields might), you won't have grades to motivate you after you complete the degree.
So mention it, but tell a valid story--something like:
"I've always been more concerned about learning than grades, although grades are important. In the UK they do _____, and this was ideal for me because I could get settled and embrace all the learning opportunities of my university without having to worry too much about a summative assessment. [Give an example of something valuable you learned that first year.] So I can understand your need to look at grades, but I'd point out that grades weren't my primary concern my first year because of the UK system, and that my GPA after that point was _____.
I don't think this feature of UK higher ed is well known in the US.