Which Credit Card Should I Use? A Checkout Guide
Which credit card should you use for a purchase? A three-step check for checkout, the traps that cost points, a wallet cheat sheet and how to automate the decision.
Key Takeaways at a Glance
- Category first: Most earn rates depend on how the merchant codes the charge (its merchant category code), not on what you buy [1]
- Caps and credits: A 4x or 5% rate can drop to 1% after a spending cap; a credit only counts if you use it
- Acceptance and fees: Some merchants take only one network, like U.S. Costco warehouses with Visa only [3]; abroad, a foreign transaction fee can cancel the reward
- Interest beats rewards: If you carry a balance, interest usually costs more than any reward earns; pay in full to keep the grace period [2]
Which credit card should you use for this purchase? With two cards it is easy; with five or more, the answer changes by merchant, by month and by how much you have already spent. This guide gives you a quick check for the checkout, the traps that cost the most points, a cheat sheet you fill once, and the cases where the card with the highest rate is not the best choice.
The three-step check
- Find the category. Dining, grocery, gas, travel, online shopping or other. The category comes from the merchant category code the business uses with the card network, for example 5411 for grocery stores and supermarkets or 5812 for restaurants [1]. See MCC codes
- Pick the highest rate you still have. Look up which card pays the most for that category and whether you already hit its cap in the current period (month, quarter or year)
- Check acceptance and cost. Network, surcharge, foreign transaction fee abroad, and interest if you will not pay the statement in full [2]
How categories really work
Card issuers do not see your receipt. They see the merchant category code that comes with the payment, and they map ranges of codes to their bonus categories [1]. That is why a supermarket inside a superstore, a coffee shop inside a bookstore or a pharmacy inside a grocery store can earn a different rate than you expect. Each issuer defines its own categories, so the same purchase can be “grocery” on one card and “other” on another.
| Purchase | Often codes as | Watch out for |
|---|---|---|
| Warehouse club | Wholesale club (5300) [1] | Many grocery bonuses exclude it |
| Gas at a supermarket station | Service station or fuel dispenser (5541/5542) [1] | Pay at the pump vs inside can code differently |
| Food delivery app | The app or the restaurant, depending on the setup | Dining bonuses may not apply |
| Hotel booked through a travel portal | The portal or online travel agency | Hotel-card bonuses often need direct bookings |
| Restaurant inside a hotel | Often lodging, not dining | Charge to the room vs pay at the table |
Your issuer’s app usually shows the category it assigned to a past purchase. Look up one charge from the merchant you are unsure about; it tells you more than any list.
Common traps
- Warehouse clubs and superstores often do not count as grocery
- Third-party delivery apps may code as the app, not the restaurant
- Category caps reset yearly, quarterly or monthly; after the cap the rate drops, often to 1%
- Rotating quarterly categories usually need activation before you spend
- Abroad, a 3% foreign transaction fee can wipe out a 2% reward. See no foreign transaction fee cards
- Some merchants accept only one network: U.S. Costco warehouses take Visa credit cards only [3]
Make a wallet cheat sheet
Fill this table once with the cards you carry and keep it on your phone. Note the cap and its period next to each card, so you know when to switch.
| Category | First card | Cap and period | Backup card |
|---|---|---|---|
| Dining | |||
| Groceries | |||
| Gas | |||
| Travel | |||
| Online shopping | |||
| Abroad | |||
| Everything else |
Update it when you add or close a card, when a cap resets, and when a rotating category changes.
A worked example
Say you hold three cards: card A earns 4% at supermarkets up to $6,000 a year, then 1%; card B earns 3% on dining; card C earns 2% on everything. A $150 grocery run in March, with $2,000 spent so far, goes on card A for $6. The same run in November, after you passed $6,000, earns $1.50 on card A but $3 on card C. Without tracking the cap, you would lose half the reward on every trip for the rest of the year.
When the highest rate is not the best card
- Signup bonus: you need to reach a minimum spend on a new card by a deadline; the bonus is usually worth far more than a few extra points elsewhere
- Protection: one card has purchase protection, extended warranty or travel insurance you want for this purchase
- Credits: a statement credit only triggers on one card, such as a dining or streaming credit
- Points value: 2 points worth 1.5 cents each beat 2.5% cash back only if you really redeem at that value
If you carry a balance, the purchase APR usually costs more than any card earns. Paying the statement balance in full by the due date generally avoids purchase interest when your card has a grace period [2].
Points or cash back: compare in cents
Rates are only comparable when they are in the same unit. Convert points and miles into cents per dollar spent: the earn rate times the value you really get per point. Use the value of the redemption you actually make, not the best case from a blog post.
| Card earns | You redeem at | Value per $1 |
|---|---|---|
| 2% cash back | 1 cent per percent | 2.0 cents |
| 3 points per $1 | 0.6 cents (gift cards) | 1.8 cents |
| 3 points per $1 | 1.0 cent (statement credit) | 3.0 cents |
| 3 points per $1 | 1.5 cents (transfer you really use) | 4.5 cents |
The same 3x card can be worse than a 2% card or more than twice as good, depending only on how you redeem. If you are not sure how you will use the points, value them at the cash or statement-credit rate your program offers.
Paying abroad and online
- Abroad, choose a card without a foreign transaction fee first, then the best rate among those
- When a terminal offers to charge in your home currency, decline and pay in the local currency; the conversion rate offered at the terminal is usually worse
- Online, a merchant’s payment processor or marketplace can set the category, so a shop that codes as grocery in person may not online
- Saved cards in shopping apps stay the default until you change them; update them when your best card for that store changes
Let an app answer it
Pointalize does this check for you: add the cards you carry from the catalog, then search a merchant or pick a category, and the Best Card Finder ranks your cards, factors in caps and rotating categories and shows the next-best card once a cap is reached. It needs no bank login. Missed Rewards shows in dollars what a purchase on the wrong card cost, so you learn where you lose points.
Check it once a month
- Open last month’s statements
- Mark every purchase where another card would have earned more
- Look for patterns: delivery apps, a warehouse club, travel booked through a portal
- Fix the cheat sheet or the app settings so the same mistake does not repeat
Two or three patterns usually explain most of the missed rewards. For merchant-specific advice, see our guides to Costco, grocery stores and gas stations.
Frequently asked questions
How do I know which card to use?
Find the merchant's category, pick the card that returns the most value below its cap (rate times what a point is worth to you), and check acceptance and fees. A card finder app does this in seconds.
What is a merchant category code?
A four-digit code a business uses with the card network, for example 5411 for grocery stores. Issuers use it to decide which bonus category a purchase earns.
Why did my grocery purchase not earn the bonus?
The store probably coded as a warehouse club or superstore, which many grocery bonuses exclude, or you passed the category cap.
Should I use a rewards card if I carry a balance?
Paying down the balance comes first. Interest on a carried balance usually costs more than the card earns.
Do I need an app for this?
Not with two or three cards: a cheat sheet works. With more cards, caps and credits, an app saves time and catches mistakes.
This guide is general information, not financial advice. Card terms change; confirm current terms with the issuer.