Where is the serial number on a Whirlpool dishwasher?

Open the door; the rating plate is fixed to the left or right side on the inside of the door.

Where the rating plate is1
  1. On the edge of the door: open it to see

Source: Whirlpool WIE 2B19 – Daily reference guide (retailer-hosted copy)

How old is my Whirlpool dishwasher?

Whirlpool doesn't publish how to read the production date from the serial number, and we haven't found a reliable rule. Ask the manufacturer's support with the model and serial number from the rating plate.

All Whirlpool appliances