Short answer

A fake IW371618 is a counterfeit of the IWC Portugieser Chronograph. The real reference sits in the IW3716xx block, the Portugieser Chronograph line that IWC moved to an in-house calibre 69355 in 2019. Counterfeits copy the case and dial shape. They do not copy the movement, the caseback engraving, or the service record. A listing that uses the exact reference number in the title and sells far below market is a warning sign, not a bargain.

Reference facts to check

Fix the specification you are comparing against before you look at photos.

  • Case diameter: IWC lists the IW3716 case at 41 mm. Measure a suspect watch with calipers. Counterfeit cases show up at 40 mm and 42 mm.
  • Movement: calibre 69355, automatic, 28,800 vph, power reserve quoted by IWC at about 46 hours.
  • Dial layout: two subdials, 30-minute counter at 12 o'clock, small seconds at 6 o'clock, date window at 3 o'clock.
  • Caseback: reference number and serial number engraved on the back. Check character shape, spacing and cut depth.

Public reference lists do not agree on every IW3716xx dial, strap and metal pairing. Confirm the IW371618 specification with an IWC boutique or the IWC service department before you pay. This guide covers the checks that apply to the whole IW3716 block.

Movement and caseback checks

Ask the seller for a photo of the movement with the rotor visible and a photo of the caseback under direct light. Counterfeit listings hide the movement and show the dial alone. A real IW371618 has a serial number that IWC can check in its own records. Call or email IWC with the reference number and the serial number. IWC answers these requests. A seller who blocks that step is selling a fake.

Dial, hands and crown

Check the printed text under a loupe. On a genuine dial the letters sit on one baseline and the stroke width is even. Counterfeit dials show uneven spacing, thick serifs, and a date window cut with rounded corners. Hands should be flat, polished on the top face, with clean edges. Run the chronograph. Counterfeit chronograph hands often snap back to a position left or right of 12 o'clock.

Unscrew the crown and wind the watch. Smooth threads that stop at a firm point match IWC case construction. Threads that feel gritty or catch point to a cheap case tube that can strip in weeks.

Price signals

The IW371618 is a stainless steel Portugieser Chronograph. New retail sits in the high four figures in USD; confirm the current figure with IWC. Used examples trade below retail, and full sets with box and papers trade above loose watches. Offers at 20 percent of retail, sellers who accept wire transfer alone, stock photos lifted from IWC product pages, and listings with no serial number photo all point to a counterfeit.

Checklist before payment

  1. Match the reference number on the caseback to the number in the listing.
  2. Ask for the serial number and confirm it with IWC.
  3. Get photos of the movement, the caseback and the clasp.
  4. Pay with a method that allows a chargeback.
  5. Meet a watchmaker for a movement check on high-value buys.

If you already bought a fake

Stop the payment if you can. Credit card chargebacks and PayPal disputes cover counterfeit goods when you file inside the window. Keep the listing page, the chat history and the photos. Report the sale to the platform. US law treats trafficking in counterfeit goods as a federal crime under 18 U.S.C. 2320, and US Customs can seize counterfeit watches at the border. A counterfeit has no IWC service record, and its parts do not interchange with IWC parts.