Filing late is a minor offence: €100 to €600. Not filing at all, or keeping no register when you should, is serious: €601 to €30,000. Those are the only two bands that apply. The six-figure penalties you will see quoted belong to different offences entirely, and the decree itself sets no fines at all.
Almost everything written about this inflates the numbers, so it is worth starting with the structure rather than the figures.
The guest-registration decree sets no fines. It sorts conduct into two categories and hands the penalties to a separate law — the Public Safety Act of 2015. Everything below comes from there.
The two bands
That is the whole of it. Two bands.
Late is not the same as never
The distinction does more work than any other point on this page, and providers routinely blur it.
What happened
Category
Fine
Filed, but after the deadline
Minor
€100–600
Details incomplete or irregular
Minor
€100–600
Did not file at all
Serious
€601–30,000
No register kept, where required
Serious
€601–30,000
A missed deadline you then met is at the bottom of that table. Not bothering is at the top. If someone quotes you €30,000 against the 24-hour deadline, they have merged the two.
Why you will see much bigger numbers
They expire
Worth knowing, and rarely mentioned.
Who pays
Liability follows the act, not the contract.
If an owner and a managing agent are both obligated parties, "we thought the other one was doing it" is a conversation between them, not a defence. See who is responsible.