Magnetic stripes are thin strips of iron-based magnetic material bonded to the back of plastic cards like credit cards, hotel key cards, and ID badges. They store small amounts of data (your account number, name, and expiration date) by arranging microscopic magnetic particles into patterns that a card reader can decode. Despite being one of the most widely used data storage technologies for over 50 years, magnetic stripes are now being phased out in favor of chip technology.
How Data Gets Stored on the Stripe
The dark or light-colored band on the back of your card is coated with millions of tiny magnetic particles. When a card is first encoded, a device called a write head passes along the stripe, generating a magnetic field that forces these particles into specific orientations, essentially flipping them to point north or south in a precise sequence. That sequence of magnetic flips represents your data in binary code.
A magnetic stripe has three separate tracks running side by side, each holding different information:
- Track 1 holds up to 79 alphanumeric characters at a density of 210 bits per inch. This is where your name, account number, expiration date, and verification codes are stored. It was originally developed by the airline industry.
- Track 2 holds up to 37 numeric-only characters at 75 bits per inch. Developed by the banking industry for financial transactions, it carries your account number and expiration date in a more compact format.
- Track 3 holds up to 104 numeric characters at 210 bits per inch and is rarely used today. It was designed for the savings and loan industry to carry additional account data.
Most transactions only need Tracks 1 and 2. The total storage capacity of all three tracks combined is tiny by modern standards, just enough for a few lines of text.
How Card Readers Decode the Stripe
When you swipe a card, the stripe passes over a small electromagnetic read head inside the reader. As each magnetized particle moves past the head, the changing magnetic field induces a tiny electrical current in a wire coil. Those fluctuations in current are amplified and converted into digital data that the reader’s computer can process. The speed and direction of your swipe matter: too fast or too slow, and the reader can’t distinguish the magnetic transitions clearly, which is why a slow, steady swipe works best.
High Coercivity vs. Low Coercivity
Not all magnetic stripes are created equal. The key difference comes down to coercivity, which is how resistant the stripe’s magnetic particles are to being erased or rewritten.
High coercivity (HiCo) stripes operate at 2,750 or 4,000 Oersted and are much harder to accidentally demagnetize. Credit cards, debit cards, library cards, and employee ID badges use HiCo stripes because they’re swiped frequently and need to last for years. These stripes are typically dark brown or black.
Low coercivity (LoCo) stripes operate at around 300 Oersted and are easier to encode but also easier to damage. Hotel key cards and gift cards often use LoCo stripes because they’re disposable or reprogrammed regularly. They’re usually lighter in color, often a tan or light brown. If you’ve ever had a hotel key card stop working after sitting near your phone for a few hours, the low coercivity is why.
What Can Erase Your Magnetic Stripe
Because magnetic stripes store data as physical magnetic orientations, any sufficiently strong external magnetic field can scramble that data. The culprits aren’t always obvious. Refrigerator door magnets, which contain strong permanent magnets to hold the door seal shut, can erase a card’s data almost instantly on direct contact. Magnetic clasps on purses and wallets pose a lower but real risk with prolonged exposure. Security tag deactivators at store checkout counters generate strong enough fields to wipe a stripe if your card gets too close. Even the electromagnetic fields from phones and cameras can interfere with a stripe over time.
HiCo cards resist casual demagnetization well. A brief brush with a phone won’t hurt them. But LoCo cards are vulnerable to fields you encounter in everyday life, which is one reason the technology is losing ground to chips that don’t have this weakness.
Why Magnetic Stripes Are a Security Risk
The fundamental problem with magnetic stripes is that they store static data. Your account number, expiration date, and verification codes sit on the stripe in the same form every time you swipe. A device called a skimmer, which criminals attach to ATMs, gas pumps, and point-of-sale terminals, can read and copy that data in seconds. Once copied, scammers can create cloned cards, make unauthorized purchases, or drain bank accounts.
Chip cards solve this by generating a unique, encrypted transaction code every time they’re inserted or tapped. Even if someone intercepts that code, it can’t be reused for another transaction. Chips also use dynamic authentication, meaning the card and the terminal verify each other in real time. This makes cloning effectively impossible with current technology.
The Phase-Out Timeline
Mastercard announced a structured timeline to retire the magnetic stripe entirely. Starting in 2024, newly issued Mastercard credit and debit cards are no longer required to include a magnetic stripe in regions like Europe where chip readers are already universal. U.S. banks will no longer need to include stripes on new Mastercard chip cards starting in 2027. By 2029, no new Mastercard cards will be issued with a magnetic stripe anywhere. The full disappearance, where no Mastercard in circulation has a stripe, is targeted for 2033.
Other card networks are following similar paths, though on slightly different schedules. The transition is gradual because millions of older card readers worldwide still rely on swipe capability, and replacing that infrastructure takes time. For now, most cards still carry both a chip and a magnetic stripe as a fallback. But within the next decade, the magnetic stripe that has been on the back of nearly every payment card since the 1970s will largely disappear.