When is the Château d'Amboise closed?

The pattern
Amboise is privately owned — see who owns it — so it does not follow the French national-monument rhythm of weekly closing days. There is no closed Monday and no closed Tuesday. What there is instead is a short winter closure, usually spanning part of late December and January, and the two fixed dates of 1 January and 25 December.
The exact winter dates move from year to year, and they are the one thing on this page I would check directly with the château if you are travelling between mid-December and early February.
Opening hours change more than closing days
The seasonal variation in hours is far larger than most visitors expect: long summer days, and a winter close that can come mid-afternoon. Arriving at four in January is a different proposition from arriving at four in July. The detail is on the opening hours page.
The days to aim at and avoid
Because it opens on Mondays, Amboise is a good Monday plan in a region where a number of sites are not. Public holidays are open and busy. The busiest days of the year are the long summer weekends and the days around 15 August; the quietest are weekday mornings in November and February. Timing is on the best time page.
There is nothing to lose by turning up without booking — there is no online entrance ticket for the château anyway, as this page explains. Just do not turn up in the first week of January.
What there is to book
Not the entrance ticket — that is bought at the château’s own desk when you arrive. What is bookable is the guiding, and the day trips that include entry to Amboise along with the other Loire châteaux.
Frequently asked questions
Is the château open on Mondays?
Yes. It is privately owned and does not have a weekly closing day.
Is it open in winter?
Yes, apart from a short annual closure and the 1 January and 25 December dates, but with much shorter hours.
Do I need to book ahead?
No online entrance ticket exists — you buy at the desk. See this page.