When is the best time to book your cruise? The answer depends on where you’re going.

The only part of your cruise where you can’t relax is in booking it. Planning on cruising Europe’s rivers next summer? Sorry, you missed the boat. Space is tight, even in the off-season.

You’re somewhat better off if planning an ocean cruise in Europe - or if you’re wanting to skirt the Alaskan coast. Ocean-going vessels have more capacity than European river cruisers, but even on big ships, it pays to book early. Savvy cruisers began booking their summer 2008 vacations in September, but take heart you procrastinator you, you’re not late - not yet.

November is still a good time to book next summer’s cruise, but don’t wait. Otherwise, “you take a significant chance,” says Rick Meadows, Holland America Line’s executive vice president marketing, sales and guest programs. “You may not get the dates or the accommodations you’re looking for.”

Be sure to ask about “off-season cruises” in Europe and Alaska, where you’ll find some of the best values, but “many of those dates go quite quickly,” Meadows says.

A good rule of thumb for when to book: nine months to a year out, unless you have your sights set on a balmy Caribbean cruise, which can be booked much closer in.