The Wertpapierkennnummer, or WKN, is Germany’s six-character alphanumeric code for identifying a security on a German exchange. WM Datenservice introduced it in 1955 and still assigns the codes today.1WM Datenservice. WKN / ISIN The ISIN officially replaced the WKN as Germany’s primary identifier in 2003, but German brokers, exchanges, and investors still use the WKN daily because six characters are faster to type and read than twelve.2Deutsche Börse. WKN – Börse Frankfurt If you are a US investor looking at German securities, you will see the WKN everywhere on German sites, and you need to know how it maps to the ISIN, how to actually buy the underlying share, and what the IRS expects from you if you do.
How a WKN Is Built
A WKN is exactly six characters long and uses digits 0–9 and most capital letters. The letters I and O are excluded to prevent confusion with 1 and 0. Early codes were purely numeric, but the system shifted to alphanumeric as the number of listed instruments outgrew six-digit numbering.3Deutsche Börse Group. WKN – Deutsche Börse AG
Every financial instrument that participates in German clearing and settlement receives one: ordinary shares, government and corporate bonds, investment funds, ETFs, warrants, and structured certificates. If it trades on a German exchange, it has a WKN, whether the issuer is German or foreign.
WM Datenservice, Germany’s National Numbering Agency, assigns every code and makes sure no two instruments share one.1WM Datenservice. WKN / ISIN Unlike the ISIN or the US CUSIP, the WKN carries no check digit of its own. Validation happens at the ISIN layer, once the WKN is wrapped into the international format.
How the WKN Maps to the ISIN
The International Securities Identification Number is the ISO 6166 global standard that replaced domestic codes as the official identifier for cross-border trades. It did not erase national codes; it absorbed them.4ISO (International Organization for Standardization). ISO 6166 – Financial Services – International Securities Identification Number (ISIN) An ISIN has three parts:
- A two-character country prefix from ISO 3166, identifying where the issuer is legally registered. German securities use “DE.”
- A nine-character basic code holding the national identifier. When the national number is shorter than nine characters, as the six-character WKN always is, zeros are inserted in front to pad it out.
- A single check digit, calculated with the modulus 10 “double-add-double” formula to catch transcription errors.
These rules are administered worldwide through the Association of National Numbering Agencies.5Association of National Numbering Agencies. Identifiers
A worked example clarifies the relationship. Siemens AG carries the WKN 723610. Its ISIN is DE0007236101. Taken apart: “DE” for Germany, “000” as padding, “723610” as the original WKN, and “1” as the check digit.6Deutsche Börse. Siemens AG Equity Knowing the WKN gets you most of the ISIN; only the final check digit requires calculation.
Both codes point to the same security, so the choice is a matter of context. International clearinghouses and foreign brokers require the ISIN. German retail platforms still default to the WKN.
How the WKN Compares to the US CUSIP
The CUSIP is the familiar US national identifier, and it feeds the ISIN the same way the WKN does. The structures differ. A CUSIP is nine characters: the first six identify the issuer, the next two describe the specific security type, and the ninth is a check digit. A WKN packs everything into six characters with no embedded issuer segment, no issue-type segment, and no check digit. It is simply a unique label assigned sequentially by WM Datenservice.
Inside an ISIN, the CUSIP fills the nine-character basic code for securities with a “US” prefix, just as the WKN fills it, with leading-zero padding, for securities with a “DE” prefix. A US investor researching a German stock will encounter the WKN on German exchange sites and the ISIN on international platforms, and will never need a CUSIP for that instrument.
How to Find a WKN
The fastest source is a German exchange’s website. Börse Frankfurt, operated by Deutsche Börse, has a public search tool that accepts a company name, WKN, or ISIN and returns the full listing.7Deutsche Börse. Equities Search Börse Stuttgart and other regional exchanges offer similar lookups. These are the most reliable references because the exchange is the point of record.
If you already hold the security, the WKN sits next to the ISIN on your brokerage asset overview, on trade confirmations, and on custody statements. German financial portals show it alongside charts and performance data.
You can also derive the WKN from the ISIN of any German security. Strip the “DE” prefix, drop the leading zeros, and remove the final check digit. For Siemens, DE0007236101 reduces to 723610.6Deutsche Börse. Siemens AG Equity
Buying WKN-Listed Securities from the United States
If you want exposure to a security identified by a WKN, you have three routes.
- American Depositary Receipts. Many large German companies have ADR programs that let you buy shares on US exchanges in US dollars. Depositary banks charge custody fees, usually a few cents per share, deducted from dividends or billed separately. The SEC puts the typical range at $20 to $50 per thousand ADRs held. A sponsoring bank can also terminate an ADR program, forcing you to sell or convert to the underlying foreign shares.8SEC. Investor Bulletin: American Depositary Receipts
- Foreign ordinary shares on US OTC markets. Some German stocks trade over the counter in the US without a formal ADR. Liquidity is lower, spreads are wider, and transaction costs are higher than for exchange-listed ADRs.
- Direct purchase on a German exchange. A handful of US brokers offer access to foreign local markets like Xetra and Frankfurt, letting you buy the actual WKN-identified shares. Liquidity is best there and you avoid ADR custody fees, but commissions are higher, you deal with currency conversion, and settlement conventions differ from US markets.
For widely traded German blue chips, ADRs are the simplest option. For smaller German issuers with no ADR, direct purchase through an international broker may be the only realistic path.
US Tax Reporting if You Own WKN-Listed Securities
Holding German securities, whether directly in a German brokerage account or through an international platform, can trigger US reporting obligations that many investors miss. Penalties are large enough to erase a year of gains.
FBAR and FATCA
If you hold financial accounts outside the United States with a combined value above $10,000 at any point during the year, you must file a Report of Foreign Bank and Financial Accounts (FBAR) with FinCEN. A German brokerage account holding WKN-identified securities counts.9Internal Revenue Service. Report of Foreign Bank and Financial Accounts (FBAR) Non-willful violations carry penalties of up to $10,000 per account. Willful violations can reach the greater of $100,000 or 50% of the account balance.
Form 8938 under FATCA is separate and kicks in at higher thresholds. For unmarried taxpayers living in the US, filing is required when specified foreign financial assets exceed $50,000 on the last day of the tax year or $75,000 at any point during the year. Married couples filing jointly get double those limits. Americans living abroad have significantly higher thresholds, $200,000 at year-end or $300,000 at any point for single filers.10Internal Revenue Service. Do I Need to File Form 8938, Statement of Specified Foreign Financial Assets?
One useful boundary: foreign stocks held in a US-based brokerage account, IRA, or 401(k) do not need to be reported on Form 8938 even if the underlying securities are foreign-issued. The account itself is with a US financial institution, so it falls outside FATCA’s foreign-account scope.11Internal Revenue Service. Basic Questions and Answers on Form 8938
Watch for PFIC Classification
Some foreign securities, particularly foreign-domiciled mutual funds and ETFs, qualify as Passive Foreign Investment Companies under US tax law. A foreign corporation is a PFIC if at least 75% of its gross income is passive or at least 50% of its assets produce passive income.12Internal Revenue Service. Instructions for Form 8621 Operating companies like Siemens or SAP rarely fall into this category, but foreign-domiciled funds routinely do.
The tax treatment is punitive by design. Gains and “excess distributions” from a PFIC are allocated across your entire holding period, taxed at the highest individual rate for each prior year (currently 37%), and hit with an interest charge on top of that.12Internal Revenue Service. Instructions for Form 8621 Form 8621 itself is complex enough that many tax professionals charge substantial additional fees to prepare it. Check PFIC status before you buy a German-domiciled fund, not after. Mark-to-market or QEF elections can soften the hit, but both require advance planning.
A small-balance exception applies: shareholders with $25,000 or less in a particular PFIC ($50,000 for joint filers) who receive no excess distributions and recognize no gains may be excused from the annual reporting portion of Form 8621, though the underlying tax rules still apply.13Internal Revenue Service. Instructions for Form 8621