Most people put every purchase on one cashback card. It's simple — but it usually leaves real money on the table. The smarter approach is what's often called "stacking": using a small set of cards together, each for the categories where it pays the most.
A typical flat-rate card pays about 1.5–2% on everything. That's fine, but category cards pay far more where it counts — for example, 6% at supermarkets, 4% on gas, or 3% on dining. If groceries and gas are big parts of your budget, earning 2% on them instead of 5–6% is a meaningful difference over a year.
A well-built stack often has three roles:
You simply use the right card for each purchase, and the catch-all handles the rest. The result is a higher effective cashback rate across your whole budget.
Stacking only pays off if you account for the details that most "best cards" lists gloss over:
Working all of this out by hand is tedious. CashStack takes your actual spending — from a quick questionnaire or a statement upload — and builds the optimal stack for you, accounting for fees, caps, exclusions, portals, and the cards you're likely to qualify for. It even shows how much more you'd earn versus the cards you already carry.