DeIQ (Decentralized IQ) provides the most accurate and reliable IQ score based on IQ data accumulated on the blockchain ledger through UCT tests. Leveraging blockchain enables IQ Olympiad to issue reliable NFT certificates to prevent the existing certificate forgery issues. In contrast to existing IQ tests where the verification process is centralized, DeIQ achieves decentralization based on blockchain. Centralization of verification forces IQ scores to be determined by one entity. On the other hand, decentralization of verification enables an individual's IQ score to be determined by all users. DeIQ incorporates the results of different IQ tests. Existing IQ tests evaluate a person's intelligence with only one or two tests, and lack a way to derive relative IQ scores by comparing test results between users. IQ Olympiad provides the combined IQ scored through its integrated IQ calculation system. DeIQ fluctuates when changes are made to the scoring table for user-created tests (UCTs) to reflect the most up-to-date data. However, when a DeIQ certificate is issued, the certificate contains the IQ at the time of issuance.