I wish there were a magic elixir you could whip up to get a free or low-cost cabin upgrade on a cruise ship. We’d be chugging it all the time. But sorry — no can do.

If you’re sitting by the phone, waiting for the upgrade fairy to call, there are a few basic things to know about upgrades. First off, understand that cruise lines deem certain cabins better than others, even within the same cabin type (inside, outside, balcony, suite). An upgrade means you’re moved to a cabin in a better category than the one you originally booked. Does that mean you will relocate from the lowest inside cabin on the ship to a balcony suite? Yeah, right, and the upgrade fairy do have wings and a magic wand. More likely, you’d be moved to a cabin that’s very similar to the one you booked but is somehow better in the eyes of the cruise line (on a higher deck, in a more convenient mid-ship location, etc.). You might not notice a difference, but you can brag about being upgraded later.

Second, free upgrades — where your cabin is relocated to a better one at no additional cost — are fairly rare. More common are “upsells,” or upgrades for a reduced cost.

But if you’re still yearning for that upgrade, how do you get one? I contend the best way to land an upgrade offer is to hope and pray because there’s little rhyme or reason to who gets a bump.

There are some strategies that have increased the odds of getting offered a cabin upgrade. The best recommendations include these five tips — and one warning why a free upgrade isn’t always what it’s cracked up to be.

1. Book a Guaranteed Cabin

A “guarantee” means you’ve assured a cabin in the category you requested, but are not assigned a specific cabin until a short time before departure — usually, a week, give or take. If you book a guarantee in a certain category and it’s full, you might get upgraded for free. On the other hand, someone else (perhaps a member of the past-passenger program with higher status) might nab the upgrade, and you’d get his or her cabin in your category. There’s no way to know.

Bottom line: Don’t book a guarantee in any given category unless you would be satisfied with any cabin in that category.

2. Cruise the Same Line Often

Just like airlines and hotels reward their loyalty program members, cruise lines do, too. An important point to remember is that the more frequent the cruiser, the more likely he or she would be offered a free or paid upgrade. Merely joining a cruise line’s loyalty program won’t get you automatically upgraded — even after you’ve taken a handful of cruises.

Complimentary or reduced-rate upgrades are generally reserved for those in the highest echelons of loyalty programs but exceptions certainly happen.

3. Book a Free Upgrade Promotion

Cruise lines occasionally offer special promotions in which two different cabin grades are priced equally — so if you book the usually pricier cabin at the lower-cabin cost, you’re theoretically getting a free upgrade. These “free upgrade” offers can either be for cabins within the same category type or from one category to another (i.e., outside cabins at inside rates or balcony cabins for outside prices).

If you truly want the inside scoop on when such a promotion might happen, book your sailing through a travel agent who’s well-versed in cruising. Travel agents get advance notice of promotions such as this and are then able to offer the upgrade to their clients. You can also sign up for cruise line promotional emails to get notices of sales in your inbox.

Sale during low demand seasons

Ships tend to sell out during peak periods. But during slow times, they may set sail with some cabins left open. Those open spots thus create wiggle room to provide passengers with upgrades.

If your off-peak cruise isn’t full and the cruise line decreases fares in an effort to boost bookings, that’s a good time to ask your travel agent or cruise line representative for a free upgrade — especially if you’re not eligible for the price reduction.

What’s considered off-peak? The periods between Thanksgiving and Christmas and right after New Year’s often see fewer bookings, in general. For specific destinations, low seasons include: May and September in Alaska (when the weather is often chillier than in the summer), September through November in the Caribbean (peak of hurricane season, kids back in school), and early January and May in the Mexican Riviera (when young ones return to school after holidays). 

5. Just ask

You’re really rolling the dice with this one, but why not just ask? What do you have to lose?

Cruise line directors or other higher-ups in the revenue department make most free upgrade decisions. If you’re willing to pay for an upgrade, call your agent or cruise line about two weeks before departure.

But make sure you work with an agent who has experience in this arena. Some have relationships with the lines or know their workings. Others do not.