Where Is the Serial Number on a Bike? How to Find, Read and Check It

Turn the bike upside down and look at the underside of the bottom bracket shell, the short tube where the crank axle passes through the frame. (In the UK the serial is often called the frame number.) Most bikes carry the serial number there, stamped into the metal or printed on a barcode sticker. If it isn’t there, check the head tube at the front of the frame, the rear dropouts, and the underside of the down tube. On some mid-drive e-bikes, Cannondale’s among them, the sticker sits behind or in front of the motor.

Once you have the number, register it free with Bike Index and 529 Garage. Buying a used bike? Search the seller’s serial on both before you hand over money. Only some brands encode the build year in the serial; the brand table below shows which ones.

Where to find the serial number on a bike

Bike Index, the nonprofit registry, says most bicycles have the serial engraved beneath the bottom bracket. Start there, then work down this list.

Full-suspension frame? The swingarm and shock can hide the bottom bracket. Santa Cruz’s instructions for its frames: remove the rear wheel, remove the lower shock bolt, then compress the swingarm until you can read the serial. When you register, Santa Cruz says to list every character on the front triangle.

Stamped digits hard to read? The Vintage Trek archive passes on an owner’s trick: rub candle wax in a color that contrasts with the paint over the stamp, wipe it lightly, and the wax stays in the grooves.

Not on the bike? Santa Cruz also prints the serial on the box the bike shipped in, and it may be on the retailer’s receipt.

Which number is the serial?

Many frames carry two or three codes, and only one is the serial. Use these rules:

• Cannondale: the serial sits on a barcode sticker and has 2 letters plus 5 numbers, 7 characters in all. Cannondale says other stickers on the down tube, with numbers in other formats or QR codes, are not the serial.
• Trek: look for a silver or grey sticker with a barcode. Trek serials typically start with a W, many with WTU. Trek’s own forms want the whole string with no spaces.
• Specialized: serials typically start with WSBC, WUD, STT or STE.
• Schwinn: the number engraved under the crank is the serial. The small silver sticker nearby holds the model number and date code.
• Huffy: the production code at the top of the white sticker under the frame (10 numbers and 1 letter) includes the serial, model number and date code. A separate Recovery Code is stamped into the frame under the crank housing. Write both down: Huffy’s manual says this information “is only available on the bicycle itself. It is not available from Huffy.”
• Brompton: the 10-digit serial is on a curved plate or sticker at the rear of the seat tube. The six-digit number stamped behind the bottom bracket is the frame number. If the serial sticker has worn off, Brompton support ([email protected]) can match the frame number to the serial.
• Two groups of characters stamped together: Bike Index’s example is a Look frame marked M4106I9CA1 and 200910427-2A, where the second group is a manufacturer number. If you can’t tell, record every group, separated by spaces.

Skip the frame hunt if you still have the receipt or a maker registration email; either may list the serial.

What year is my bike? What the serial number can tell you

Only some makers build the date into the serial. Trek publishes no key for its current serials and can identify a bike only if it was registered, though older stamped Trek serials can be dated. Specialized says its serials don’t indicate size, model or year. Schwinn and Brompton publish a key. Check your brand before you trust a “serial number decoder” site.

Reading a Schwinn date code

Schwinn lists these year letters for its current sticker:

• 2019: AI
• 2020: BJ
• 2021: BA
• 2022: BB
• 2023: BC
• 2024: BD
• 2025: BE

So a code ending in 1503BC reads as 15 March 2023 under Schwinn’s key (day first, then month). For bikes from 1976 on, some Schwinns also carry a four-digit Julian date on the head badge: the first three digits are the day of the year and the last digit is the year. A badge reading 2156 would be day 215 of a year ending in 6, which is early August (our worked example; the badge alone can’t tell 1976 from 1986). Schwinn’s serial records from before August 18, 1948, were lost in a factory fire, so a pre-1948 bike may need the crankset removed to find a stamped date inside.

Dating a Trek, Huffy or other brand without a key

Parts narrow the window when the serial won’t, and they confirm a decoded serial when it will. Our Trek 1000 guide shows how to date an older Trek from its crank, shifters, fork and Trek’s own catalogs, then settle it with the stamped serial. For a Huffy, keep the production code for parts orders, and our look at whether Huffy bikes are any good covers the model families and warranty terms that code unlocks.

Register your serial number

Registration ties your name to the serial before anything happens. In the US, that runs through free private registries like the ones below, and police departments can enroll with 529 Garage to search its records in the field. Register with more than one.

Bike Index holds more than 1.85 million registered bikes. As of October 15, 2026, it listed 182,265 of them as stolen and 18,422 as recovered. That works out to about 1 in 10 stolen listings recovered (our math).

What to record

• The serial, exactly as stamped, plus any second code beside it.
• Make, model, color and frame size.
• Photos of the serial, the drive side of the bike and anything that sets it apart: scratches, stickers, a swapped saddle.
• For an e-bike, the battery serial from its type label. On a Bosch smart system e-bike, the eBike pass in the Flow app stores the frame number, documents and photos in one place.
• The receipt. Ask the shop to print the serial on it.

Keep copies away from the bike: a photo in cloud storage, and the registry record itself.

Check a used bike before you buy

A search only finds bikes someone registered. BikeRegister points out that its check “will not help if the original owner did not register their bike.” Run it anyway: it takes two minutes and catches the ones that were.

1. Ask for the serial before you meet. A seller with nothing to hide can read it off the frame. Treat a refusal as a reason to walk away (Icebike’s rule).
2. Search Bike Index and 529 Garage. In the UK, add BikeRegister’s BikeChecker. Bike Index treats look-alike characters such as 0 and O, or S and 5, as the same, but it doesn’t do partial searches, so type the full serial. If the frame has two codes, search each one.
3. Read the frame yourself at the meeting. The stamped serial must match the one you searched and any receipt the seller shows.
4. Walk away from a ground-off, filed or painted-over serial, or a frame where the serial sticker has been cut or scraped away. In California, knowingly buying or possessing a bicycle whose serial number has been removed or altered is a crime under Penal Code 537e, punishable by up to six months in county jail for property worth $950 or less. Other states have their own rules.
5. Check e-bike batteries. Bosch invites buyers to enter a battery serial on its battery check page before buying, to see whether Bosch holds any information on that battery. A Bosch e-bike marked stolen in the Flow app is identified as stolen goods, Bosch says.
6. Sanity-check the price. Run the bike through our bike resale value calculator. A price far below that range needs a reason you can see, like damage or missing parts.
7. Get a written receipt with the serial, the date, the price and the seller’s name and phone number.

For the mechanical side of a used purchase (frame cracks, wheel wear, drivetrain checks), see our guide to buying a used road bike.

What to do if your bike is stolen

Few owners report theft, and few get their bikes back. A 2025 study in the journal Findings estimated that about 2.4 million adult bicycles are stolen each year in the US, against 157,669 bikes reported stolen to police in 2019. In a 2023 survey of 1,823 theft victims in the US and Canada, recruited mostly through Bike Index, 17% of theft incidents were reported to police and 15% of stolen bikes were recovered. Act in this order:

1. File a police report and write down the report number. Registries and insurers ask for it, and Schwinn releases registration details to police only on a written request.
2. Mark the bike stolen on Bike Index and any other registry you used. Report it stolen on 529 Garage, which pushes a Missing Bike Bulletin to riders nearby.
3. For a Bosch smart system e-bike, mark the bike and battery as stolen in the eBike Flow app and generate the digital theft report to send to police or your insurer.
4. Watch online marketplaces. In the same 2023 survey, 27% of recovered bicycles had been sold online, most often on Facebook in the US (9%) and Kijiji in Canada (8%).
5. Call the police when you spot it. Give them the listing and your report number rather than meeting the seller alone.
6. Tell your insurer, if a homeowner’s, renter’s or bike policy covers it.

To make the next theft less likely, our bike theft prevention guide covers locks, storage and where thieves strike.

Questions riders ask

Is there a bike serial number lookup?

Two kinds. A stolen-status lookup is open to anyone: Bike Index, 529 Garage’s Check a Bike and, in the UK, BikeRegister’s BikeChecker. A lookup of model and year sits with the maker: the Cannondale App fills in details for most bikes from model year 2019 on, Trek can identify a bike only if it was registered, Schwinn and Brompton print the date in a code you can read yourself, and Specialized can’t tell the model or year from the serial.

Is the serial number the same as the model number?

No. Schwinn prints the model number and date code on a silver sticker and engraves the serial into the frame. Huffy’s sticker code bundles the serial, model number and date code together, with a Recovery Code stamped in the frame. Register the serial, and add any other code in the notes.

Is a bike serial number the same as a VIN?

Bicycles don’t have a VIN. The federal VIN rule (49 CFR Part 565) covers motor vehicles such as cars, trucks, trailers and motorcycles. On a bike, the frame serial does the same job: it identifies that one frame for registries, police and insurers.

Can I look up who owns a bike by its serial number?

The public can’t. Bike Index and 529 Garage show whether a bike is reported stolen, and Bike Index lets you message the owner through a stolen listing. Makers like Schwinn share owner details only with the owner or with police.

Do all bikes have serial numbers?

Nearly all. Bike Index says bikes without one are rare and are usually handmade or very old.

What if my bike has no serial number?

Register it anyway with photos and a description. A 529 Shield adds a unique 7-character ID you can register, and in the UK BikeRegister uses its own marking ID.

My bike was stolen and I never wrote the serial down. Can I get it?

Check the receipt, the shop that sold it and any maker registration email. Trek can identify a bike from its serial only if you registered it, so the shop’s sales record is often the best lead.

Sources

• Bike Index. Bike Serial Numbers (accessed October 15, 2026). Bottom bracket as the usual location, head tube, dropout and Schwinn non-drive dropout examples, manufacturer number vs serial, search rules.
• Bike Index. Home page statistics and About (accessed October 15, 2026). 501(c)(3) status, registered, stolen and recovered counts.
• Bike Index. How to Get Your Stolen Bike Back (accessed October 15, 2026). Stolen listings, police and pawn industry databases.
• Project 529. 529 Garage, 529 Shield and For Law Enforcement and Cities (accessed October 15, 2026). Free registration, optional Shield with 7-character ID, Check a Bike, field app, 15-mile bulletins.
• BikeRegister. BikeChecker (accessed October 15, 2026). Free check by frame number or marking ID and its limits.
• Trek Bicycle. Contact Us FAQ and Project One Owners Club (accessed October 15, 2026). Sticker location, W and WTU prefixes, serial identifies a bike only if registered.
• Specialized. FAQ (US) and FAQ (Canada) (accessed October 15, 2026). Serial locations and prefixes; serial does not indicate size, model or year.
• Cannondale. Where do I find my bike’s serial number? and The Cannondale App does not find my bike serial number (accessed October 15, 2026). Barcode format, e-bike sticker location, model year 2019 and later.
• Schwinn. Where is the model number, date code or serial number of my bike?, What’s my bike’s age and value and My bike was stolen (accessed October 15, 2026). Locations by era, date code key, year letters, registration release to police.
• Huffy. Bike FAQs and Owner’s Manual for Cruiser Bicycles (m0001, 2017) (accessed October 15, 2026). Production code on the white sticker includes serial, model number and date code; Recovery Code stamped under the crank housing; information not available from Huffy.
• Brompton. How Do I Find My Frame and Serial Number? (accessed October 15, 2026). Ten digits, first four are year and month.
• U.S. Consumer Product Safety Commission. Brompton Bicycle Recalls Bicycles Due to Fall Hazard (December 21, 2017). Serial on a curved plate or sticker at the rear of the seat tube; six-digit frame number behind the bottom bracket; [email protected] matches a frame number to its serial.
• Santa Cruz Bicycles. How to Find Your Serial Number (accessed October 15, 2026). Full-suspension steps, e-bike location, shipping box and receipt.
• Vintage Trek. Trek Frame Serial Numbers (archived August 18, 2025). Enthusiast decoding tables for stamped Trek serials, stamp locations, serialization date vs model year, candle wax tip.
• Code of Federal Regulations. 49 CFR Part 565, Vehicle Identification Number (VIN) Requirements, section 565.2 Application (accessed October 15, 2026).
• Bosch eBike Systems. eBike battery check and Digital theft protection (accessed October 15, 2026). Battery serial on the type label, digit counts by generation, mark as stolen, eBike pass, theft report.
• State of California. Penal Code section 537e (accessed October 15, 2026). Property with a removed or altered serial number; bicycles included in subdivision (b).
• Agarwal, S., Fitch-Polse, D. T., Nelson, T. and Herr, S. Bicycle Theft in the US: Magnitude and Equity Impacts. Findings, January 2025.
• Cohen, A., Nelson, T., Fitch-Polse, D., Schattle, E., Herr, S., Zanotto, M. and Winters, M. Patterns in Bike Theft and Recovery. Findings, November 2023.