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How does credit/debit card numbering work?

How does credit/debit card numbering work?

How does credit/debit card numbering work?

The number on a bank card, which could be a debit or credit card, is made up of various segments of numbers strung together. Usually, a bank card number is 16 digits in length, and the standard format of a bank card number is controlled under the ISO/IEC 7812 international standard published by the International Organization of Standards.

Let’s get cracking at the code itself. The first digit of any card number is the Major Industry Identifier (MII). For all financial/banking-related cards, this is 4, 5 or 6. So the code on your bank card begins with one of these numbers only. Other numbers are assigned to other sectors.

The next 5 digits, along with the first one, make up the Issuer Identification Number (IIN). These identify the banks or organizations issuing the card. Different banks have different ranges of IIN, for instance, MasterCard numbers all begin with the digits 51,52,53,54,55.

Credit and debit card numbering follows a specific format known as the Bank Identification Number (BIN) or Issuer Identification Number (IIN). The numbering system is standardized, and each part of the card number serves a particular purpose.

Here’s a breakdown of how credit/debit card numbering works:

  1. Issuer Identification Number (IIN/BIN): The first six digits of a credit/debit card are known as the Issuer Identification Number (IIN) or Bank Identification Number (BIN). These digits identify the issuing institution or bank. For example:
    • Visa cards typically start with a “4.”
    • Mastercard numbers start with a “5.”
    • American Express cards start with “34” or “37.”
  2. Account Number:
    • The digits following the IIN constitute the account number. The length of the account number can vary, but it typically ranges from 10 to 12 digits.
  3. Check Digit:
    • The last digit of the card number is known as the check digit. It is calculated using the Luhn algorithm (modulus 10 algorithm) and is used to verify the integrity of the card number.
  4. Additional Numbers:
    • Some cards have additional numbers, such as the Card Verification Value (CVV) or Card Verification Code (CVC). The CVV is a three-digit code on the back of Visa and Mastercard cards, while American Express cards have a four-digit code on the front.
  5. Expiration Date:
    • The expiration date is also part of the card information. It indicates the month and year until which the card is valid.

The structure of credit/debit card numbers is standardized to ensure consistency and compatibility with various financial systems and card processing networks. It’s important to note that while the card number identifies the card and its issuing institution, it does not contain information about the cardholder’s account balance or other sensitive details. The security of cardholder information is maintained through encryption, secure transmission, and other security measures implemented by card issuers and payment processors.

The next 9 digits, simply enough, identify a particular account in the bank/organization.

The last digit is usually a checksum. A checksum is a digit that is the result of performing some calculations on the other digits in the code. It is used to check the correctness of the code. This works in the following way: you use an algorithm to perform calculations on the other digits to form a value, and add that as the 16th digit. This number can be checked to detect various kinds of errors in the rest of the code that can occur during transmission.

The most popular method used for computing the checksum digit of a bank code is the Luhn Algorithm, defined in Annexure B of the 7812 standard. It can detect most single-digit errors in the code.

That makes your 16 digits.

In addition to this, another code on credit/debit cards is the Card Verification Value or the Card Security Code. This code is used now for validating transactions where the card/card holder is not physically present, to effectively verify that the card is indeed in the holder’s hand, also used as a substitute for the PIN.

Nowadays, almost all cards have the CVV printed in small letters on the back of the card. The CVV is generated by combining personal information like the holder’s PAN number, service code, and expiration date of the card, together, using encryption algorithms like the Data Encryption Standard (for Visa cards) and encryption keys known to the issuer, and then encoding the result as a three-digit code.

How does credit/debit card numbering work?

 I’ll add just two more points that may also be helpful to you if you’re trying to understand bankcard numbering from a more practical (versus purely technical) perspective.

  1. Not all bank card numbers are 16 digits in length. As one of many examples, American Express card numbers have only 15 digits. Others range from a low of 12 to a high of 19.
  2. As Himanish indicated, the Major Industry Identifier or first digit in the card number can be used to identify the card network although you may also have to look at the second digit (the first number in the Issuer Identification Number) to complete that network identification process. Cards beginning with 34 or 37 will bear the brand of American Express, 4 will have the Visa brand, 51 through 55 will have the MasterCard brand and many of the cards beginning with 6 will bear the Discover brand. Wikipedia (Bank card number) offers a much more complete list if you’re interested in or need more detail.
  3. Although I don’t believe there is any industry requirement or rule for it, I’ve worked for a couple of issuers that used the first two digits after the MII and IIN to segregate the card population by product type. For example, an issuer might use 00 for non-reward credit cards, 01 for reward credit cards, 02 for premium rewards credit cards, and 03 for debit cards. This greatly limits the number of available, unique card numbers, however, and thus only works if the issuer has a relatively small population of cards within each product type.

Is it true that magnetic strips on your debit and credit cards are not encrypted and if a skimmer has been installed in the point-of-sale terminal, your card and possible bank information could be compromised?

Yes, this is true; credit card magnetic stripes are not encrypted. And perhaps more to the point, even if it weren’t true — even if magstripes were encrypted with the most fiendish scheme that could be devised — it would be of no help whatsoever.

The fundamental problem with magstripe credit cards is that the information on the magnetic stripe doesn’t change. The terminals in stores only read the card. They cannot and do not write to it.

So let’s suppose that your credit card had a magnetic stripe with encrypted data. And let’s suppose that I, a criminal, want to commit some crimes. Here’s how this would play out:

  • I install a skimmer at a point-of-sale terminal. This has become disturbingly easy to do; modern skimmers are incredibly small and can be installed without having to open up the terminal.
  • You make a purchase using that terminal. My skimmer reads the fiendishly-encrypted data from the magnetic stripe.
  • Later on, I collect the data from the skimmer, including your card’s fiendishly-encrypted data.
  • I make absolutely no attempt to decrypt the fiendishly-encrypted data.
  • Instead, I simply write the fiendishly-encrypted data, unmodified, onto another credit card.
  • Now I start making purchases using that credit card.
  • The point-of-sale terminal reads your fiendishly-encrypted data from my card and transmits it to the bank.
  • The bank approves the transaction.
    • It has to.
      • Because the encrypted information on my card is exactly the same as the encrypted information on your card. To the bank’s computer, my card and your card look exactly the same.
  • So I don’t need to know what information is on the back of your card. All I have to know is that it will cause my transactions to be approved, because if it didn’t, then your card wouldn’t work for you.
  • So the fiendish encryption of the card data is pointless.

This is why banks and merchants are spending so much money trying to push people kicking and screaming into using a chip-and-PIN system. Because the chip-and-PIN system is much, much more secure. Without going into the technical details, here are the key points:

  • Chip-and-PIN transactions don’t actually use the credit card number printed on the card. Instead they revolve around a secret that’s embedded in the chip and can’t be extracted.
  • Every time you perform a chip-and-PIN transaction, the terminal tells the chip what PIN you entered; the chip creates transaction data, which will only be correct if the PIN is correct.
  • Every time you perform a chip-only transaction — with no PIN entered — the chip still generates transaction data.
  • The terminal sends the transaction data to the bank.
  • Since the bank knows the secret, the bank can verify that the transaction data is legitimate. But nobody else along the line can.
  • For reasons that are pretty technical, I can’t simply record the transaction data that the chip generates during one transaction and use it again later.

So in general, it’s not possible — well, at least not financially viable — to perform these types of fraud with a chip-and-PIN-based card.

Of course, in the United States, the Achilles’ heel of all this is that we still perform Internet transactions the old-fashioned way, without the chip. So that’s a continuing source of vulnerability for these cards.

What’s the best way to keep your credit score high with just a debit card?

A debit card will do absolutely nothing for your credit score. Bank accounts don’t appear on credit reports, and a debit card is merely an alternative to writing a check.

Here’s a better idea for getting the best credit score: use a credit card for all or most of your day-to-day purchases. Pay it off in full each month to avoid having to pay interest.

If you can’t get approved for an unsecured card or because you have no credit history, get a secured card from your bank or credit union.

Credit cards are extremely useful and convenient. They are by far the easiest way to build credit—and they won’t cost you a penny if you pay them off each month.

Is it possible to use a debit or credit card without swiping it?

Credit and debit cards come in plenty of colors and each has a special feature attached to it. Right from the basic cards to the premium cards that charge a hefty annual fee. Credit and debit cards come in plenty colors and each has a special feature attached to it. Right from the basic cards to the premium cards that charge a hefty annual fee. However, there is a new symbol that can be found on credit and debit cards these days which looks like the symbol that denotes WiFi, just in the horizontal position.

If you have this symbol on your card, it means your credit or debit card has the contactless feature and can be tapped to pay. Contactless cards don’t necessarily need to be swiped to make a transaction. These cards come with a Near Field Communication (NFC) chip that allows short-range data transfer without the need to touch the point of sale (PoS) device.

As per Visa’s official website, “Contactless payments use short-range wireless technology to make secure payments between a contactless card or payment-enabled device and a contactless-enabled checkout terminal. When you tap your card on a PoS machine with a contactless symbol, your payment is sent for authorization.” Visa claims a contactless card works when it is within 4cm of the PoS and that the contactless payment terminal can only process one transaction at a time.

This payment technology is growing in developed countries. According to a report by Independent, one in every four card payments has been done using a tap to pay card. Visa claims, apart from the US, over half of retailers in countries like Australia, Canada, the UK, and France accept contactless cards.

In India, the trend has been catching up and many supermarkets have started using PoS machines with the tap-to-pay symbol.


  • Using tap to pay is quicker than the usual card swipe
  • Don’t need to give your card away
  • No need to punch in a PIN for amounts up to Rs 2000
  • Leaves a digital trail of expenditure

How does credit/debit card numbering work?

Is there a better alternative to debit and credit cards?

Yes, there are! UPIs and related payment gateway services can come to your rescue. For an inside scoop, do read on!

As the modern world is evolving rapidly with digitization people tend to go cashless and prefer other payment mediums. Although cash is the obvious alternative to debit and credit cards it is certainly not what most people prefer.

While the former era has always managed to pay their dues through debits and credit cards issued by their bank the new era enables an advancement. Payments now can be conducted through smartphones with an application that offers electronic wallets. Popular platforms such as Google Pay PayTM enables any individual to fulfill their monetary transaction with a single press of a mobile.

The new solutions have been a fruitful endeavor offering an easy mode of payment. If paid with credit or debit you first have to look for an ATM counter and then get the required cash. Also, there was the factor of safety of those cards as they might get in the wrong hands accidentally which might lead to theft or burglary.

There were a lot of things you had to worry about while using a debit or a credit card regarding safety and its other issues. Using phone applications as a method of payment is easy to conduct while providing the necessary assurance of safety.

Why should you use credit cards and not debit cards?

This is an interesting one, most people aren’t aware of.

Once you make a payment with a debit card to a retailer, whether online or high st, or book a hotel room, and they take your card details, if you have any disput1e, you will not be able to do much at all, unless you wanna go through a long process. The hotel can take a full night’s cost, if you can’t show up because, you fell ill, even though they promised there are no cancellation fees, they can take money from your card, the one you gave for verifying.

Credit card is very consumer friendly, in this area… all dispute are covered. Careful, about where and to who you give your debit card details, especially online.

When is it better to use a debit card as opposed to a credit card?

There are many aspects to this.

  1. Which country do you live in? In certain countries like the US, building a credit score is important so one prefers to use credit to increase their score while in other countries like India, this is not the case
  2. How much liquid cash do you need to keep? If using a debit card brings you cash below what you want (maybe because you expect a big expense coming up or for an emergency) – perhaps use a credit card to delay shelling out directly from your bank account
  3. Frauds. These can be quite prevalent depending on where it’s being used. For example, I used my debit card in Hong Kong airport and days later a large sum got deducted without my authorization on my debit card. Turns out there are machines that copy your information. It eventually got refunded but we had to file a complaint and chase the bank which can be a pain. Prefer using a credit card when traveling abroad as you can choose to not pay the bill after necessary follow-ups with the bank with genuine proof and the risk is not on you
  4. Cashback/points/deals – this is obvious. Compare which card gives you more benefits. I have the new Apple Card which gives 2% instantaneous cash back. Some other credit card gives movie ticket discount, shopping deals, etc.
  5. Late payment interest also matters but it’s beat to avoid law payment altogether

How did someone get my debit card information?

There have been a few posts. Your card or numbers were stolen physically. A scammer called and was able to get that from you which is unlikely since you would have likely realized you gave out the numbers. There is a even more likely event. I used to work for an online company and had a customer call in and said that the only two places their brand new credit card were used with our company and Amazon. Now that company I worked for had never had a breach and Amazon who knows, but since it was only ever used in those two places only one thing was connecting, the device used to order from Amazon/us.

So if you’ve entered in the card information for any online ordering, whether that’s for Amazon, WalMart, or any other online retailer and it was used for fraud shortly after that, I would assume you downloaded a keylogger which is recording everything and transferring that to any number of places. I suggest looking up on google “how to find and remove a keylogger” I use malware bytes anti-malware and Avira anti-virus but there are plenty of other descent programs to help.

Can I learn my debit card number without my debit card?

Not unless you have it in your hand. Usually comes in 2 parts….the card and then the pin # and activation code. You can’t actually use the card until you set it up. If it’s a checking acct with the debit attached you can go to the bank and write a check to access your money. Most businesses won’t accept the starter checks you get when you open the acct, but your bank will.

It usually takes about 10 working days to get your card and checking acct established and working. This is why you don’t 9ut a large amount, if money in the startup. Most people open the acct with $50 or $100.

How do I get a 6-digit ATM card number?

Congratulations on becoming the latest member of the Quora “criminal wannabe” club!

Some banks are now requiring 6-digit PINs or use 6-digit one-time codes. For an ATM card you are authorized to use, the issuer either allows you to set the PIN or supplies the OTP app.

But you knew that, right? Somehow you got a hold of one or more stolen ATM cards and want to steal someone else’s money. Well, the issuers require such codes just to thwart crooks like you. If there was any easy way to obtain them, issuers would use something else.

So by asking your question, you show you lack the common sense or street smarts to be a successful thief. Full-time consideration of another endeavor might be in order.

Hope this helps

What is a POS debit card transaction?