Cashback cards are among the easiest financial products to compare, because the comparison is arithmetic and the arithmetic is not difficult. What makes them confusing is that almost everybody runs the sum in the wrong direction: they start from the offer and try to imagine spending that fits it, rather than starting from their spending and finding the offer that fits.
Run the right way round, the answer usually surprises people. A card advertising a high rate in one category frequently returns less over a year than a modest flat rate applied to everything, because the impressive number sits on spending you do not do much of. This piece is about how to run that comparison, and nothing in it is financial advice — it is arithmetic you can check yourself.
Start with your statements, not the offers
Download twelve months of statements and sort the spending into rough categories: groceries, fuel, travel, dining, utilities, everything else. Twelve months matters because spending is seasonal, and a three-month sample taken over a summer will overstate travel and understate heating.
You now have the only input that matters. Every offer can be evaluated against it directly, and the exercise takes about twenty minutes once rather than being repeated every time an advertisement appears. If sorting the transactions by hand sounds tedious, a budgeting app will do the categorising for you.
Two things usually become obvious immediately. The first is that spending is far more concentrated in one or two categories than people expect. The second is that a substantial share falls into categories no card rewards at all — rent, mortgage, council tax, and anything that cannot be paid by card without a fee.
The comparison, done properly
Take each candidate card and multiply your actual annual spending in each category by that card’s rate for the category. Add it up. Subtract any annual fee. That number, and only that number, is what the card is worth to you.
| Step | What to do | Common mistake |
|---|---|---|
| 1. Categorise | Twelve months of real spending | Using a typical month, which does not exist |
| 2. Apply rates | Each card’s rate against each category | Applying the headline rate to everything |
| 3. Apply caps | Most enhanced rates are capped | Ignoring the cap, which is where the value goes |
| 4. Subtract the fee | Annual fee, and any foreign transaction charges | Comparing gross rather than net returns |
| 5. Check the exclusions | What does not earn at all | Assuming all spending counts |
Caps are where most of the disappointment lives. An enhanced rate that applies to a limited amount of spending per month or per quarter converts a headline figure into a modest fixed sum, and once you are past the cap the card frequently earns less than a flat-rate alternative would have on the same spending.
Introductory rates and what happens afterwards
Many cards offer a raised rate for an initial period. That is genuinely worth something, and it is worth exactly what it says: a fixed benefit over a fixed window, after which the card reverts to its standard terms.
The mistake is treating the introductory rate as the card’s value. If you intend to keep a card for years, the standard rate is what matters and the introductory period is a rounding error. If you are willing to move regularly, the introductory rate is the point — but then you are running a different strategy, with its own admin and its own effect on your credit file.
Be honest about which of those you are. Most people intend the second and do the first.
Sign-up bonuses sit in the same category and are usually the largest single number attached to a card. They are also one-off, conditional on a minimum spend within a window, and frequently structured so that meeting the condition requires bringing spending forward or inventing it. A bonus you reach naturally is free money. A bonus you reach by spending more than you would have is not a bonus at all, and the arithmetic that makes this obvious is the same arithmetic as everywhere else on this page.
The part that undoes everything
Cashback is calculated as a percentage of spending. Interest on a balance carried month to month is calculated at a rate that is, in every case, dramatically higher. If you do not clear the balance in full, the interest overwhelms the reward comprehensively and the card becomes an expensive way to borrow with a small discount attached.
This is the single most important sentence in the piece: a cashback card only makes sense if you clear it every month, without exception. If there is any chance you will not, the correct product is a card with a low interest rate and no rewards, or no card at all.
The same logic applies to spending more because a card rewards it. A percentage back on a purchase you would not otherwise have made is not a saving; it is a discount on money you did not need to spend.
Who this isn’t for
Skip cashback cards entirely if you carry a balance, or if you have found in the past that having credit available changes how much you spend. Both are common and neither is a character flaw; they simply make this product the wrong tool.
Skip them too if your spending is dominated by things cards do not cover — rent, mortgage, tuition. If most of your outgoings cannot earn cashback, the maximum achievable return may not justify the annual fee or the administration.
And skip the complexity if you know you will not track it. A multi-card strategy that returns marginally more but requires you to remember which card to use where is a strategy most people abandon within months, at which point the flat-rate card you rejected would have earned more.
What to know before you buy
- Use twelve months of your own statements as the input. Everything else is guesswork.
- Find the caps before the headline rate. They usually decide the outcome.
- Compare net of fees, including foreign transaction charges if you travel.
- Check the exclusions. Utilities, tax and rent are commonly excluded.
- Only proceed if you clear in full monthly. Interest destroys the arithmetic.
- Prefer simplicity unless the extra return is large enough to justify the tracking.
Is a flat-rate card ever better than a category card?
Frequently, yes — particularly where spending is spread across categories, or concentrated in one that no card rewards well. It is also better for anyone who will not track which card to use where, because a flat rate cannot be used incorrectly.
Does cashback affect my credit score?
The cashback itself does not. Applying for cards leaves a record, and opening several in a short period can affect how lenders view an application. If you expect to apply for a mortgage or a loan soon, that is worth factoring in.
Are annual-fee cards worth it?
Only if your calculated return exceeds the fee by a comfortable margin — and the margin should be comfortable, because spending changes. A card that breaks even on last year’s spending will lose money on a quieter year. The same framework applies as in five questions before any large purchase, and the fine-print habit is the one described in reading a zero percent offer.
The whole category rewards twenty minutes of arithmetic and punishes reading advertisements. Sort your spending, apply each card’s actual rates and caps to it, subtract the fees, and pick the largest number. If the largest number is small, the honest conclusion is that no cashback card is worth the effort for you, which is a perfectly good outcome to reach.
