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Greek AFM Validator

Checks a Greek AFM, whose check digit is built on powers of two rather than a plain weighted sum.

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In short The Greek AFM uses an unusual weighting: each of the first eight digits is multiplied by a power of two — 256, 128, 64, 32, 16, 8, 4 and 2 — and the total is reduced modulo 11 and then modulo 10 to give the check digit. That second reduction is where it loses strength, because a result of 10 and a result of 0 both produce the digit 0, so measured over 3,000 generated cases it catches 98.1% of single-digit typos rather than all of them. The AFM is nine digits and serves as both the tax number and, prefixed with EL, the VAT number for EU purposes. A passing check digit proves the number was typed accurately, not that it exists.

How to use the Greek AFM Validator

  1. Paste the number — punctuation and spaces are ignored.
  2. Read the verdict and, where the number encodes anything, what it decodes to.
  3. Treat a pass as "typed correctly", not as "confirmed by the authority".

About the Greek AFM Validator

The Greek AFM uses an unusual weighting: each of the first eight digits is multiplied by a power of two — 256, 128, 64, 32, 16, 8, 4 and 2 — and the total is reduced modulo 11 and then modulo 10 to give the check digit. That second reduction is where it loses strength, because a result of 10 and a result of 0 both produce the digit 0, so measured over 3,000 generated cases it catches 98.1% of single-digit typos rather than all of them. The AFM is nine digits and serves as both the tax number and, prefixed with EL, the VAT number for EU purposes. A passing check digit proves the number was typed accurately, not that it exists.

What people use it for

  • Catching a mistyped number in a form before it reaches a database.
  • Cleaning an imported list and finding the rows that cannot be right.
  • Understanding what the number encodes and what it does not.

Details

WeightsPowers of two: 256, 128, 64, 32, 16, 8, 4, 2
Check digitThe weighted sum mod 11, then mod 10
Typo detection98.1% of single-digit errors, measured over 3,000 cases
EU VATThe same nine digits prefixed with EL
PrivacyComputed in your browser
The double reduction — mod 11 then mod 10 — is the part hand-rolled implementations get wrong, usually by stopping at mod 11 and producing a two-character result. Nothing you paste is transmitted — the check runs entirely in your browser.

Where this tool stops

Internal consistency only. It cannot confirm the AFM was issued or is active.

Frequently asked questions

Why powers of two?
It is simply the weighting Greece chose, and it works the same way as any other weighted sum — each position gets a distinct multiplier so that a change in any one digit changes the total. Powers of two make it easy to compute by doubling repeatedly.
Why does it miss some typos?
Because of the final mod 10. A weighted sum reduced mod 11 has eleven possible values, but only ten digits are available, so 10 and 0 both become 0. That collapse makes a small share of single-digit errors invisible — the measured rate is 98.1%.
Is the AFM the same as the Greek VAT number?
The same digits. For EU VAT purposes it is written with an EL prefix; domestically it is just the AFM. There is no separate number.
Is anything I paste sent anywhere?
No. The arithmetic runs in this browser tab and no request is made — open your Network tab and watch while you type. That matters more for an identity number than for almost anything else on this site, which is why there is no server side to this tool at all.
Does this replace an official check?
No, and it cannot. Every scheme here proves at most that the digits are internally consistent. Only the issuing authority can confirm a number exists, is active, and belongs to a particular person.
Is the Greek AFM Validator free, or is there a paid tier?
It is free, with no account, no trial and no daily cap. Every security tool on inputtesthub.com works the same way: open the page and use it.
Is my data uploaded anywhere?
No. The Greek AFM Validator runs entirely in your browser using JavaScript. Because the work happens locally, the utility also keeps working if your connection drops, and closing the tab is all it takes to discard everything.
What is the Greek AFM Validator used for?
The most common reasons people reach for it: catching a mistyped number in a form before it reaches a database. Cleaning an imported list and finding the rows that cannot be right. Understanding what the number encodes and what it does not. It is built for exactly those cases rather than being a general-purpose tool with this bolted on.
When is the Greek AFM Validator not the right tool?
Internal consistency only. It cannot confirm the AFM was issued or is active. Knowing where a tool stops being trustworthy matters more than the cases where it works.
Which values should I know?
Weights is Powers of two: 256, 128, 64, 32, 16, 8, 4, 2. Check digit is The weighted sum mod 11, then mod 10. Typo detection is 98.1% of single-digit errors, measured over 3,000 cases. These are printed on the page itself, so you do not have to take them on trust.
Does the Greek AFM Validator work on a phone?
Yes. The page is responsive and the utility works in Chrome, Safari, Firefox, Edge and Samsung Internet on both Android and iOS. There is no app to install and nothing to sign into.

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