Size and depth: the Certificate is roughly half the credits (about 34 vs 60 at OTHM), covering core theory with limited clinical assessment; the Diploma is the full qualification with the supervised 40+ case portfolio and observed assessments. When insurers, employers or universities say ‘Level 7’, they almost always mean the Diploma.
The Certificate suits practitioners who want the theoretical grounding at postgraduate level without the full portfolio commitment, and it is a legitimate stepping stone. But check what your insurer and intended employers recognise before choosing it as a destination. The market’s default meaning of ‘Level 7 qualified’ is the Diploma, and upgrade routes from Certificate to Diploma vary by awarding body. We enrol most candidates directly onto the Diploma for exactly that reason, and say so before taking a deposit.