Insert a single leading zero into whichever segment is one digit short: 4-4-2 pads the first segment, 5-3-2 pads the second, 5-4-1 pads the third — always producing a 5-4-2 code, and never simply adding a zero to the front of the whole number.
Convert an NDC
Try , , .
Why the conversion exists at all
HIPAA electronic transactions define a fixed-width 11-digit NDC field. The FDA never required a uniform width, so its codes come in three shapes. Every 10-digit code therefore has to be normalised before it goes on a claim.
Medicaid drug rebate reporting and Medicare Part D claims use the same 11-digit form, which is why the conversion is unavoidable rather than a payer preference.
The three rules
| Source format | Pad this segment | Before | After |
|---|---|---|---|
| 4-4-2 | First | 0002-7510-01 | 00002-7510-01 |
| 5-3-2 | Second | 50242-051-01 | 50242-0051-01 |
| 5-4-1 | Third | 0169-4132-1 | 0169-4132-01 |
Then strip the hyphens. 00002-7510-01 transmits as 00002751001.
The two ways people get it wrong
Both errors produce syntactically valid output, which is what makes them dangerous: nothing rejects them at entry, and the mismatch surfaces later as a denial or an audit finding.
Where the converted code goes on a claim
On a CMS-1500 the shaded portion of box 24A carries the N4 qualifier immediately followed by the 11 digits, with no space or hyphen, then the unit qualifier and the quantity administered. On an 837P the same data sits in the LIN and CTP segments.
Questions
Is the 11-digit NDC ever printed on the package?
Rarely. Packages carry the FDA 10-digit form. The 11-digit code is a billing construct, which is why it has to be derived rather than read off the carton.
Do all payers require 11 digits?
All HIPAA-covered electronic claims do. A 10-digit code in an 11-digit field is normally rejected at the clearinghouse rather than denied by the payer.