Why Retailers Ask for Your Zip Code

Most stores ask for your zip code when you pay by card. Without blinking, we rattle off our digits. Here's the surprise: the zip code isn't needed for the transaction to go through. The cashier is collecting it for marketing — pure and simple.

What do stores actually do with your zip code?

Forbes contributor Adam Tanner wrote in 2013 about refusing to give his zip code to a cashier at the Mob Museum in Las Vegas — and the cashier's shock, saying nobody had ever refused before. Tanner went on to write a whole book, What Stays in Vegas, about how American companies harvest personal data.

Here's the mechanism: the retailer already has your name from the card. Add a zip code, and data brokers can often pin down your exact address. Then come the flyers and mailers — from every store, restaurant, museum, and bakery where you ever swiped your card and handed over those five digits.

Are you required to give it?

No. You are not required to give a zip code, email address, or phone number to complete a purchase. (The one exception: if the back of your card is unsigned, the clerk may legitimately ask for ID to verify your identity.) Consumer advocates have long advised saying no to any information beyond what the transaction needs — a shipping address for delivery, for instance, or a Social Security number when opening a line of credit.

What about your email address?

Same story. When the checkout asks for your email, it's collecting it to send store promotions. The store wants to reach you even when you're not shopping — that's marketing, not customer service.

So the next time the cashier asks for your zip code, remember: it's not for the transaction. It's for the mailing list. If you'd rather not get the hundred junk mails and coupon flyers, just say no.