DUCR Number Builder 2026 — Check Yours Before CDS Rejects It
Build a valid Declaration Unique Consignment Reference, or check the one you already have. The tool validates the format against HMRC guidance — the 35-character limit, the 18-character reference and the characters HMRC prohibits.
Format per HMRC — Simplified Customs Declaration Process · page updated 26 Mar 2026 · read 19 Sep 2026
GB prefix./ and colons : must not be used.Where it goes: the DUCR belongs in data element DE 2/1 of your declaration. The same number must appear on the SFD and on the SD — mismatched references between the two are a frequent cause of rejection. HMRC recommends sequential numbering, as it makes a missing consignment easy to spot.
Frequently asked questions
What is a DUCR made up of?
A DUCR follows the format <year><GB><EORI>-<reference>. The year is the last digit of the year it was allocated (6 for 2026), GB is the country of allocation, followed by the EORI number, a hyphen and the trader's own reference. The whole number must not exceed 35 characters.
Which characters are not allowed in a DUCR reference?
The reference may contain only digits 0–9, capital letters A–Z, a hyphen and brackets. HMRC explicitly prohibits forward slashes and colons, which is a common mistake when copying an invoice number across. The reference is limited to 18 characters.
Where does the DUCR go on a customs declaration?
The DUCR is entered in data element DE 2/1. The same number must appear on the simplified frontier declaration (SFD) and on the supplementary declaration (SD) for that consignment.
Does this tool check whether a number has already been used?
No. The tool validates the format only and does not connect to any customs system. Uniqueness is guaranteed by the trader whose EORI the DUCR contains.
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Message us on WhatsAppThis tool checks the format of a number against HMRC guidance. It does not connect to any customs system and cannot tell you whether a reference has already been used — uniqueness is guaranteed by the trader whose EORI the DUCR contains.