einvoice-preflight now has a Denmark page, the 22nd in its country set.
Searching for "Denmark e-invoicing deadline" returns confident answers that conflict. One source says every business over DKK 300,000 turnover must e-invoice from 1 January 2026. The better-documented ones say there is no such rule. Denmark's route is the Bookkeeping Act: businesses must keep books in a registered digital system, phased in from July 2024 to January 2026. Those systems must produce SAF-T 2.0 files from 1 January 2027, and users are to be registered on NemHandel, the Danish Peppol network, by default. Sources give 1 July 2026 or 1 March 2027 for that, and the amending rules were still in consultation until 17 August 2026.
The page lays out each date next to who reports it, marks draft text as draft, and says what the checker does not do (OIOUBL, NemHandel BIS 4, SAF-T). The Danish Business Authority's own site was unreachable from the build container, so every date is from secondary sources. That is stated on the page.