A Common App essay is written to reveal something about your character, background, or personal growth. A UCAS personal statement needs to show your academic interest in a specific course. You may be able to reuse some ideas or examples, but the statement should be rewritten for UCAS.
They are trying to do different jobs
The Common App essay is personal and applicant-focused, while the UCAS personal statement is course-focused.
A Common App essay might discuss personal growth, identity, family, values, challenges, or formative experiences. Those can work well in a US application, but they are the wrong centre of gravity for UCAS.
UCAS wants academic evidence
A UK admissions tutor needs to see why you want to study the subject, how you have explored it, what you have learnt from that exploration, and whether you are prepared for degree-level study.
Those points should drive the structure of the statement. A strong UCAS statement should be academically engaged with the course you are applying for, not a personal essay with the course added near the end.
Most Common App essays use the wrong structure
The structure is built for a different admissions system.
A Common App essay starts with a story, builds towards a personal lesson, and uses that experience to show character.
A UCAS personal statement should start from the course. The evidence should show subject interest, academic preparation, and readiness for the demands of the degree.
That means the same experience may need to be used differently.
Reuse material, not the essay
You can reuse relevant material from a Common App essay, including reading, research, projects, academic competitions, work experience, volunteering linked to the course, or a moment that sparked your subject interest.
But do not reuse the structure. Take the useful evidence and rebuild it around the UCAS course. Ask what each example proves about your academic interest or preparation.
Remove the personal essay elements
A UCAS statement does not need a dramatic opening, life lesson, or broad explanation of who you are.
Cut material that focuses mainly on personality, resilience, family background, moral values, identity, childhood memories, emotional turning points, or general life experience.
Those details may be powerful in a Common App essay. In UCAS, they take space away from the academic argument your statement needs.
What a UCAS version should do instead
A stronger UCAS statement should explain what draws you to the subject, which ideas, topics, or questions interest you, what you have done to explore those interests, what you learnt from that exploration, how your current studies prepare you, and why the course is the right academic next step.
Final advice
Do not copy your Common App essay into UCAS.
Start with the course, then select the experiences, reading, projects, and evidence that explain why you want to study it.
If your finished UCAS statement still reads like a personal essay about you, it has not been properly rewritten for UCAS.