The supermarket chain has been trialling quiet hours in a small number of stores over the last year after one of its staff with an autistic child suggested it would be a good idea.
The initiative will be rolled out nationwide from October 23.
During the quiet hour, noise, lighting and other distractions instore will be reduced.
That includes switching off the store radio, lowering checkout volumes, and keeping trolley collection and shelf-stocking to a bare minimum.
Countdown's general manager of corporate affairs, safety and sustainability Kiri Hannifin said they had had positive feedback from many customers about the quiet hour trial.
"We know grocery shopping can be an anxiety-inducing experience for some customers and we wanted to help with that. By making a few small changes and creating a quiet hour, we hope we can make a big difference," she said.
"Our older customers seem to really enjoy quiet hours too, as well as many other Kiwis who actually just find shopping a bit stressful and can now visit at a more peaceful time."
The quiet hour will run from 2.30pm on Wednesdays at most Countdown stores.
Countdown Silverdale and Countdown Northwest will hold their quiet hour from 9am to 10am.
At this stage, Countdown's two metro city stores will not hold a quiet hour.