The gap test
Look at where your current card earns its lowest rate, then check how much you spend there. If a meaningful share of your budget is sitting in that low-earning bucket, a second card aimed at exactly that category is doing real work. If it is not, you are adding admin for nothing.
Two cards, two clear jobs
The setup that actually holds up over time is simple: one card for a category where you spend heavily, one flat-rate card for everything else. The moment you need a rule more complicated than that, you will stop following it within a month.
The hidden costs of more cards
Each additional account is another due date, another set of terms and another opportunity to miss a payment. Missed payments cost far more than optimised earning rates gain. Complexity has a real price and it is usually underestimated.
The best card setup is the one you will still be using correctly in two years, not the one that maximises a spreadsheet today.
Timing the application
Space applications out rather than clustering them. Give a new account time to settle and report before adding another, particularly if your file is still relatively young.
When to stop at one
If your spending is spread fairly evenly with no dominant category, a single strong flat-rate card is genuinely the right answer. There is no prize for carrying more cards than your budget justifies.
