How long must I live in Denmark before I can apply for permanent residence?

Denmark's permanent residence rules are national and not based on the EU Long-Term Residents Directive (which Denmark does not apply). The standard requirement is 8 years of continuous lawful residence, reduced to 4 years if you meet all of Denmark's supplementary conditions (such as a higher Danish language test, an employment-history requirement, active citizenship and an income threshold). You must also pass the Prøve i Dansk 2 language test, be employed at the time of decision, have no disqualifying criminal record or significant overdue public debt, and not have received certain social benefits. Processing can take up to 12 months.