Chelmsford — 01245 dialling code

About the 01245 dialling code in Chelmsford

01245 is the geographic UK area code anchored on Chelmsford, Essex, listed in Ofcom’s National Telephone Numbering Plan. The code reaches across the wider charging area surrounding Chelmsford rather than the town centre alone. When an inbound UK landline shows +44 1245 on Caller-ID, the originating exchange is most likely physically located in or near Chelmsford, with neighbouring exchanges on 01200, 01202, 01204.

Numbers in Chelmsford’s 01245 block were originally allocated to UK communications providers in 1,000-number sub-ranges (the legacy Ofcom block size for geographic codes), with newer allocations issued in 10,000-number blocks once the smaller blocks ran out. Each block is delegated to a Range Holder — typically Openreach (BT), Virgin Media O2, Sky, Gamma Telecom or one of a long tail of regional carriers — who is then responsible for assigning individual numbers to end-customers in the Chelmsford charging area. The full table further down this page shows every currently-allocated range on 01245 and the holder it was delegated to.

This is the same data Ofcom publishes every Wednesday in the public UK Numbering Data feed; we re-ingest the snapshot weekly, so the Chelmsford allocations you see here are at most seven days old. Because UK numbers are portable, the current carrier of any specific 01245 number in Chelmsford can differ from the Range Holder shown — see Range Holder vs current provider for the explanation. To identify a specific caller, paste the full number into the lookup above: you’ll get the Range Holder, the allocation status, the Chelmsford area-code metadata, and a live AI internet check summarising any public web reports about that exact number.

From abroad, a Chelmsford 01245 number is reached by dialling the international access prefix (00 from most of Europe, 011 from North America), then 44, then the local digits with the leading zero dropped. So a number written locally as 01245 123 4567 becomes +44 1245 123 4567 when dialled from outside the UK. Inbound calls to a Chelmsford landline are charged at the recipient’s standard call-receive rate (free in most consumer tariffs), and outbound calls from a UK mobile or landline to a 01245 number are billed at the caller’s own UK landline rate. Essex consumers and businesses with a 01245 CLI typically use Openreach copper or fibre, Virgin Media O2 cable, a Sky or TalkTalk retail bundle, or one of a long tail of regional or VoIP-based providers — the table further down this page shows the wholesale allocation that anchors each block, but the live retail carrier on a specific number can be different after porting.

If you have just received a missed call from a 01245 number and you don’t recognise it, the most reliable next step is to paste the full number into the lookup above before calling back. The Ofcom Range Holder data tells you which wholesale carrier the block was issued to, which often gives away whether the call is a local resident, a national business renting a Chelmsford-presenting CLI, or a VoIP service that could be operating from anywhere in the UK. The AI internet check then aggregates any public reports about the specific digits — Reddit threads, MoneySavingExpert forum posts, Trustpilot reviews, scam-reporting databases — so you have context before you decide whether to ring back.

01245 by the numbers

Chelmsford is one of 11 geographic dialling codes in Essex. The 01245 dialling code serving Chelmsford has 200 number ranges on file across 29 distinct Ofcom Range Holders, of which 60% are in active Allocated status. The allocated prefixes run from +44 12450 through +44 1245537.

The visible blocks on 01245 are predominantly geographic (01 / 02) (100%). A number sitting inside an Allocated 01245 block is in active service with a UK customer in or near the Chelmsford charging area, whereas one claimed to come from a Reserved, Designated or Free block almost certainly isn’t the genuine origin and points instead at a spoofed Caller-ID worth treating with caution. The full table below lists every visible block and the Range Holder it was delegated to.