When must a new DMCC company register for UAE corporate tax?

Generally within 3 months of incorporation, even if it expects to pay nothing (confirm your date with your specialist). Late registration carries an AED 10,000 penalty, which the Federal Tax Authority may waive if the first tax return is filed within 7 months after the first tax period ends. We register the company as part of setup.

Source: Corporate Tax registration service, Federal Tax Authority, UAE