SEDOL vs ISIN: Differences, Conversion & When to Use Each

Last updated: March 2026 · 12 min read

If you work with UK or international securities, you've encountered both SEDOL and ISIN codes. While both identify financial instruments, they serve different markets and have distinct structures. This guide breaks down every difference, shows you how to convert between them, and explains which one to use in different situations.

1. Side-by-Side Comparison

2. What Is a SEDOL?

SEDOL stands for Stock Exchange Daily Official List. It's a 7-character identifier created and maintained by the London Stock Exchange Group (LSEG). Originally designed for securities traded on the LSE, SEDOL has expanded to cover instruments globally — though it remains most commonly associated with UK and Irish markets.

SEDOL Structure

SEDOL:  B H 4 H K S 3
        ^ ^ ^ ^ ^ ^ ^
        ├─────────┤ │
        6 chars     Check digit
        (alphanumeric, no vowels)

Key rules for SEDOL codes:

• No vowels allowed — SEDOL codes never contain A, E, I, O, or U to avoid forming words
• Old SEDOLs (pre-2004) are purely numeric and start with 0–9
• New SEDOLs (post-2004) start with a letter (B, C, D, etc.) to expand the namespace
• The check digit uses a weighted sum with weights 1, 3, 1, 7, 3, 9, followed by modulo 10

Who Uses SEDOL?

• Fund managers tracking UK and European equity positions
• Custodian banks for settlement of LSE trades
• Data vendors — Bloomberg, Refinitiv, and FactSet all support SEDOL as a key identifier
• SWIFT messages — SEDOL is a recognized identifier in MT54x settlement messages
• Index providers — FTSE Russell uses SEDOL extensively for index construction

3. What Is an ISIN?

ISIN stands for International Securities Identification Number. Defined by ISO 6166, it's the global standard for identifying securities. Every country has a National Numbering Agency (NNA) responsible for assigning ISINs — in the UK, this is the London Stock Exchange itself.

ISIN Structure

ISIN:   G B 0 0 B H 4 H K S 3 9
        ^ ^   ^ ^ ^ ^ ^ ^ ^ ^ ^
        │ │   └─────────────┘ │
        │ │    9-char NSIN    Check digit (Luhn)
        └─┘
        Country code (ISO 3166-1 alpha-2)

The 9-character National Securities Identifying Number (NSIN) in the middle is country-specific. For GB securities, the NSIN is built from the SEDOL code padded with leading zeros.

4. How SEDOL and ISIN Are Related

This is the most important thing to understand: for UK securities, the ISIN literally contains the SEDOL. The relationship is:

GB-ISIN = "GB" + "00" + [SEDOL] + [Check Digit]

Example (Vodafone):
  SEDOL:  BH4HKS3
  ISIN:   GB  00  BH4HKS3  9
          ──  ──  ───────  ─
          Country Pad SEDOL  Check

Example (HSBC):
  SEDOL:  0540528
  ISIN:   GB  00  0540528  5
          ──  ──  ───────  ─
          Country Pad SEDOL  Check

What About Irish Securities?

Irish securities use the country code "IE" in their ISIN. The SEDOL is still used in the NSIN portion, but the prefix changes:

CRH plc (Irish building materials):
  SEDOL:  0182704
  ISIN:   IE  00  0182704  0

5. How to Convert Between SEDOL and ISIN

SEDOL → ISIN (Algorithmic for GB Securities)

For GB-listed securities, you can derive the ISIN from a SEDOL in three steps:

1. Prepend "GB00" — the ISO country code for the United Kingdom plus two padding zeros
2. Append the SEDOL — all 7 characters including the SEDOL check digit
3. Calculate the ISIN check digit — using the Luhn algorithm (convert letters to numbers: A=10, B=11, ..., Z=35, then apply double-alternate-sum mod 10)

Step-by-step: SEDOL BH4HKS3 → ISIN

1. Construct: GB00BH4HKS3?
2. Convert letters: G=16, B=11, B=11, H=17, H=17, K=20, S=28
   → 16 11 0 0 11 17 4 17 20 28 3 ?
3. Apply Luhn algorithm → check digit = 9
4. Result: GB00BH4HKS39

ISIN → SEDOL (Simple Extraction for GB Securities)

If you have a GB-ISIN, extracting the SEDOL is trivial:

ISIN:   GB00BH4HKS39
             ───────
             Characters 5-11 = SEDOL
             
Result: BH4HKS3

Automated Conversion Tool

For bulk conversions or non-GB securities, use our free tools:

• SEDOL → ISIN Converter — works for all securities in our database
• ISIN → SEDOL Converter — including non-GB securities
• Batch Converter — convert up to 50 identifiers at once

6. When to Use SEDOL vs ISIN

Rule of Thumb

7. Real-World Examples

Here are SEDOL and ISIN pairs for well-known securities:

8. How They Compare to CUSIP, WKN & Other Identifiers

SEDOL and ISIN are part of a larger ecosystem of financial identifiers. Here's how they all fit together:

Think of ISIN as the universal wrapper — it takes the local identifier (SEDOL in the UK, CUSIP in the US, etc.), adds a country code, and appends a check digit to create a globally unique code.

For detailed comparisons with other identifiers, see:

• ISIN vs CUSIP: Key Differences
• German Securities Identifiers (WKN & ISIN)
• Swiss VALOR Numbers Explained
• Complete Financial Identifier Conversion Guide

9. Frequently Asked Questions