A 4.0 GPA is right in UC San Diego's admitted middle-50% GPA range of 3.85–4.0.
That puts you in the typical admitted band. It's a solid baseline, but GPA alone won't get you in — the rest of your profile carries real weight here.
A GPA is the single biggest academic factor, but it's necessary, not sufficient — especially at a 28.4%-acceptance school like UC San Diego. Your test scores, course rigor, extracurriculars, essays, and any standout achievements all move the number. The estimate above assumes typical scores and rigor; your real odds depend on your full profile.
Estimates are CDS-based and for a typical applicant. Run your full profile for your real, calibrated odds.