I run Sweepbase, a small site that compares crypto debit and credit cards. It's a Next.js app that reads one CSV file instead of a database, and every couple of weeks I re-pull the data and re-check the claims. The cashback column is the one that always gets me.

Here's the shape of it across 136 active cards (5 of the 141 I track are dead now): 88 advertise some kind of cashback, and 43 of those slap a number of 5% or higher on the marketing page. The top of the list says 100%, 90%, 85%.

You've shopped for a normal card. You know 2% flat is already a good deal. So how does a crypto card "pay" 100%?

It doesn't, not the way the hero image wants you to read it. That number is usually a first-purchase promo capped at a few dollars, or a staking tier where you lock up the native token and the "cashback" is really just yield on money you parked. Sometimes it only applies to one spending category up to a tiny monthly cap. The everyday, no-strings rate on most cards sits somewhere between 0.5% and 2%.

Then there's the part that never makes the marketing page: FX markup. A card can shout "0% fees" and still take 1-2% on anything outside your home currency. Spend abroad and your "3% cashback" quietly becomes about 1.25% after the conversion. On a card you'd actually travel with, the markup can eat the reward whole.

I'm not saying skip crypto cards. I'm saying read the cashback line like you'd read a function's edge cases: what's the cap, what triggers the rate, and what's the fee waiting on the other side.

I keep a sortable list of crypto cards with cashback and update it as rates move, with the real everyday rate, the caps, and the FX sitting next to each other. It's open data, so you can pull it and check my math.

— Mihail B.