Key Points:

• A points blogger discovered that adding his Amex Platinum card to a National Car Rental profile inflated a 10-day Cancun rental from $133.79 to $654.33, a $520 swing.
• The issue traces back to third-party discount codes and status perks stacking incorrectly with base rates, not a flaw unique to Amex.
• Readers should always price-check rentals both with and without their elite status or discount codes attached before booking.

Most of us add our premium credit cards to rental profiles assuming the built-in discounts and elite status can only help. A recent real-world example proves that assumption wrong. One traveler pricing a 10-day rental at the Cancun airport found that having his Platinum Card® from American Express linked to his National Car Rental profile pushed the price to $654.33, while the same car booked in an incognito browser, with no card or status attached, came in at $133.79. That is not a rounding error. It is a $520 lesson in why elite perks deserve a second look before you assume they are saving you money.

What Actually Happened

The Amex Platinum card comes loaded with rental car perks: complimentary Avis Preferred Plus, Hertz President's Circle, and National Emerald Club Executive status, plus a 20 percent discount code through National. On paper, that should mean a cheaper rental, not a more expensive one.

In this case, the card's linked discount code appears to have overridden a much cheaper base rate rather than stacking on top of it. When the traveler logged out entirely and searched the same dates anonymously, National's own base price was roughly five times lower than the "discounted" rate tied to his Amex Platinum profile. Removing the card from his account, then rebooking, let him lock in the lower rate.

This is not necessarily an Amex-specific glitch. Rental agencies run dozens of overlapping promo codes, corporate rates, and loyalty discounts at once, and the algorithm does not always pick the lowest one. Any status or discount code, whether it comes from Amex Platinum, Chase Sapphire Reserve, or a co-branded airline card, can theoretically cause the same problem.

Why This Matters for Points and Miles Travelers

If you carry a premium travel card specifically for perks like complimentary elite rental car status, this is worth paying attention to. The entire value proposition of cards like the Amex Platinum depends on those perks actually functioning as discounts, not silently inflating your total.

For travelers who rent frequently, especially on international trips where local rate structures behave differently than domestic ones, a five-figure price gap on a single booking can wipe out an entire year's worth of card-related savings. This is exactly the kind of hidden cost that a rewards optimization strategy is supposed to prevent, not cause.

How to Protect Yourself Before You Book

Run this quick check every time you rent a car, regardless of which card or status you're using:

• Search the rental in a normal browser while logged into your loyalty account with your card attached.
• Open an incognito or private browser window and search the identical dates, location, and car class with no account or card linked.
• Compare both totals, including taxes and fees, not just the headline rate.
• If the logged-out rate is lower, call the rental agency or use a travel advisor to confirm whether the discount can be applied on top of the base rate instead of replacing it.
• If not, book the cheaper rate and skip the "discount" entirely. You can typically still request elite upgrades and perks at the counter using your loyalty number, even on a rate that did not include the discount code.

This five-minute habit costs nothing and has the potential to save hundreds of dollars per rental, particularly on international bookings where pricing tends to be less transparent.

The Bottom Line

Elite status and discount codes are supposed to work in your favor. This case is a reminder that "supposed to" and "actually does" are not always the same thing, and the only way to know for sure is to check. Before your next rental, do the side-by-side comparison above rather than trusting that your premium card is automatically getting you the best deal.

If you're building out a car rental strategy around your points and miles cards, our Amex Platinum review breaks down whether the $895 annual fee still pencils out once you factor in real-world quirks like this one. This article contains affiliate links. If you apply through our links, we may earn a commission at no cost to you, which helps us continue sharing points and miles strategies with the community.