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IMEI

Everyday

International Mobile Equipment Identity

The 15-digit number that uniquely identifies a mobile device, ending in a Luhn check digit, used to track, block, or verify phones.

Definition

The IMEI (International Mobile Equipment Identity) is a 15-digit number that uniquely identifies a physical mobile device, independent of the SIM card or phone number in use. Carriers and law-enforcement systems use it to track, block, or unblock a specific handset, which is why checking a phone's IMEI against blacklist databases is a standard step before buying one secondhand, and why tools like the IMEI Validator exist to confirm the number is structurally valid in the first place.

Formula

The 15th and final digit of an IMEI is a Luhn check digit, calculated using the same algorithm used for credit card numbers:

  1. Starting from the rightmost digit (the check digit itself, excluded from this step) and moving left, double every second digit.
  2. If doubling a digit produces a number greater than 9, subtract 9 from it (equivalent to summing its two digits).
  3. Sum all 14 resulting digits.
  4. The check digit is whichever value (0-9), when added to that sum, produces a total that's a multiple of 10.

Worked Example

Take the 14-digit body 4917271284**3239** for illustration, running it through the Luhn doubling-and-summing steps above produces a specific check digit that makes the full 15-digit number pass validation. The IMEI Validator performs this exact calculation automatically when you paste in a number.

Key Things to Know

  • Always 15 digits: a valid IMEI is exactly 15 digits long, with the final digit existing purely as a Luhn check digit rather than part of the device's identifying data.
  • Same checksum as credit cards: the Luhn algorithm behind an IMEI's check digit is identical to the one used for Check Digit-verified payment card numbers, just applied to a different length of string.
  • *Dial #06# to retrieve it: this shortcode works on nearly every phone regardless of manufacturer or carrier.
  • Dual-SIM phones have two: each SIM slot gets its own independent IMEI, sometimes labeled IMEI1 and IMEI2.
  • Checked before resale, unlike a VIN's checksum: IMEI validation typically matters most at the point of buying a used device, similar in spirit to how a VIN check protects a used-car buyer, though the two use different checksum formulas.

Related Terms

Check DigitCheck Digit (Identifier Validation)VINVehicle Identification Number

Frequently Asked Questions

Where do I find my phone's IMEI number?
Dial *#06# on almost any phone and it displays instantly, or check Settings > About Phone, the original box, or underneath a removable battery. Once you have it, the [IMEI Validator](/imei-validator/) can confirm it's structurally valid before you rely on it.
Why does it matter when buying a used phone?
Checking the IMEI lets you confirm the device isn't reported lost or stolen and hasn't been blacklisted by a carrier, since a blacklisted IMEI means the phone won't connect to most networks even with a new SIM card. It's one of the first checks worth doing before paying for a secondhand device.
What's the difference between IMEI and IMEI2?
IMEI2 simply refers to the second IMEI number present on dual-SIM phones, since each SIM slot gets its own independent 15-digit identifier. The [US IMEI Validator](/imei-us-validator/) handles standard single or dual-SIM IMEI checks the same way.
How is the last digit of an IMEI calculated?
It's a Luhn check digit, computed by doubling every second digit from the right, subtracting 9 from any result over 9, summing all 15 digits, and choosing the check digit that brings that total to a multiple of 10, the same algorithm used to validate credit card numbers.
Can two phones ever have the same IMEI?
In theory no, since IMEIs are meant to be globally unique per device, though counterfeit or unlocked phones sometimes ship with duplicated or invalid IMEIs, which is exactly the kind of problem a validity check catches before you buy.