IMEI Comparison Tool for TAC and Checksum Matching

The IMEI Comparison Tool checks two supplied identifiers side by side. It validates each value, compares all fifteen positions and reports whether the TAC, serial portion and check digit are identical. The calculation is useful when checking a phone against packaging, repair paperwork, inventory records or another trusted copy of the identifier.

Everything happens locally in the browser. The comparison does not search a global database and does not determine which value belongs to a genuine device. It answers a narrower and reliable question: are these two entered strings structurally valid, and where do they differ?

What the comparison includes

The first eight positions are compared as the Type Allocation Code. Positions nine through fourteen are compared as the serial portion, and position fifteen is compared as the Luhn check digit. The result lists every differing position so that a one-digit transcription error is easy to locate.

Both values are also validated independently. Two identifiers can be different while both pass the checksum, or they can look nearly identical while one fails. Matching text alone is therefore separate from mathematical validity.

Useful comparison situations

A buyer can compare the value shown in the phone's settings with a trusted label or purchase record. A repair team can compare intake and return records. An inventory manager can investigate mismatched exports without uploading identifiers to another service. On a dual-SIM phone, IMEI 1 and IMEI 2 are normally different, so a difference does not automatically indicate a problem.

Always consider the source of both values. Matching an untrusted screenshot with an untrusted listing proves very little. The strongest comparison starts with the identifier displayed by the physical phone and evidence you can independently inspect.

What matching IMEIs do not prove

An exact match does not establish ownership, warranty, carrier-unlock state, blacklist status or authenticity. It only establishes that the two supplied values are the same after permitted formatting normalization. A copied or altered label can still display matching text.

For a purchase decision, combine the comparison with physical inspection, account-lock checks, official manufacturer support and the legitimate blacklist process available in the relevant country.

How to compare two values

1. Paste exactly two IMEIs, separated by a line break, comma or space.
2. Confirm that each normalized value contains 15 digits.
3. Review the independent checksum status of both entries.
4. Inspect the reported differing positions and structural sections.
5. Resolve any mismatch before relying on the associated record.

How an IMEI comparison is performed

A reliable comparison begins with normalization rules that are narrow and visible. Spaces and ordinary display hyphens may be removed, but digits must never be reordered, guessed or silently replaced. Each normalized value is then checked for exactly fifteen decimal digits before its Luhn result and structural fields are calculated. Only after those independent checks should the two strings be compared position by position.

The tool reports exact equality and the number of changed positions. It also groups the comparison into TAC, Serial Number and check-digit sections. This makes a mismatch more understandable than a single red badge. A difference in position 4 belongs to the TAC; a difference in position 11 belongs to the SNR; and a difference in position 15 affects the displayed check digit.

Comparing the Type Allocation Code

Positions 1 through 8 make up the TAC under 3GPP TS 23.003. GSMA documentation explains that TAC is allocated for a device type and is used within the official IMEI ecosystem. When two IMEIs have different TAC values, their allocated device-type identifiers differ. That does not automatically tell a browser the exact commercial model, because accurate model resolution requires maintained allocation data.

Comparing the six-digit serial portion

Positions 9 through 14 form the SNR within the TAC. Two standard IMEIs for different physical units would normally differ somewhere in the combined TAC-and-SNR body. A dual-SIM handset can legitimately expose IMEI 1 and IMEI 2 as different equipment identities, so “different” is not synonymous with “fraudulent.” The correct interpretation depends on why the records were expected to match.

Comparing the Luhn check digit

Position 15 is the human-readable check digit calculated from the first fourteen digits. If the bodies match, the mathematically expected check digit also matches. If only the entered final digit differs, at least one displayed value fails the formula unless both strings contain some earlier normalization problem. Validate both values rather than choosing the one that looks more familiar.

Checksum comparison boundary

The Luhn formula detects many ordinary entry errors, but it is public and non-cryptographic. Two values can both pass while referring to different equipment identities, and an intentionally constructed number can pass without proving that a genuine handset carries it.

Source quality matters more than visual equality

Comparison evidence is only as strong as its sources. A value read directly from the phone's settings or device information screen generally provides better evidence than text copied from an advertisement. A label on packaging is useful when the packaging can be linked reliably to the phone. A seller-controlled screenshot can be altered or taken from another unit, so matching two seller-provided images should not be treated as independent confirmation.

For repair intake, preserve when and how each identifier was captured. “Read from device before repair” and “read from device after repair” are more informative labels than “old” and “new.” For inventory, store identifiers as strings, retain leading zeros and avoid spreadsheet transformations. For purchasing, perform the comparison while the physical phone is available and before transferring money.

Evidence hierarchy for comparison

A practical evidence hierarchy starts with the physical device, then trusted intake or purchase records, original packaging or invoices, and finally secondary screenshots. Conflicting evidence should trigger investigation, not an automatic verdict.

Understanding common comparison outcomes

An exact match means the normalized strings are identical. It does not mean the handset is authentic, paid off, unlocked or absent from a blacklist. A one-position mismatch often suggests a transcription problem, especially when one value fails Luhn. Multiple mismatches may indicate that records from different devices were combined, but the tool cannot determine intent.

Matching TAC with different SNR fields is consistent with different units from the same allocation. Different TAC values can be consistent with different device types or allocations. Matching first fourteen digits with different final digits indicates inconsistent check-digit text. Two valid but completely different IMEIs simply represent two mathematically valid identifier strings; further context is required.

Dual-SIM and multi-device considerations

On dual-SIM equipment, do not assume IMEI 1 and IMEI 2 should be identical. Compare each identifier with the correspondingly labelled record. Similarly, a smartwatch, tablet or secondary connected device can have its own identifier. A shared account, phone number or data plan does not collapse multiple physical devices into one IMEI.

Comparison workflow for used-phone checks

1. Display the identifier on the phone using the manufacturer's documented method.
2. Record whether it is IMEI 1 or IMEI 2.
3. Compare it with the corresponding packaging or transaction record.
4. Validate both strings and inspect every reported difference.
5. Resolve unexplained mismatches with the seller or responsible organization.
6. Continue separately to official warranty, account-lock and blacklist checks.

This sequence prevents a format check from becoming an all-purpose “clean phone” claim. The comparison tool establishes string and structure relationships only; it does not have access to time-sensitive external records.

Privacy and operational handling

Avoid pasting production IMEI lists into public collaboration tools merely to compare two values. Local browser processing keeps the submitted text out of this site's server flow, but the identifiers can still be exposed if the computer is shared, the result is screenshotted or the user copies it into an untrusted message. Mask examples when complete values are unnecessary.

For organizations, limit access to staff with a defined purpose, set retention periods and separate identifiers from unrelated customer information.

Research references

The 8-6-1 display structure and Luhn purpose follow ETSI 3GPP TS 23.003 Release 19. TAC allocation and database-resolution limits are supported by the GSMA IMEI Database overview.