The IGCSE is opted for grades 9-10, whereas the IBDP for grades 11-12. Hence, the most obvious difference is their difficulty levels as they are taken up by different age groups.
IGCSE merits students based on a three-tier grading system— Distinction, Merit, and Pass. Whereas, IB uses a points system (the perfect score is 45 points), where 24 points and above secures an IB Diploma.
The IB provides a much more holistic education. It not only conducts exams but also emphasises on writing and developing critical thinking skills. Students are required to engage in research and much more in the form of internal assessments, the extended essay and TOK. The IB requires you to have good time management skills and provides a holistic development, whereas the IGCSE is more straightforward and focuses on teaching subject specific content and tests your knowledge through exams.