Employees will work 34 hours over the four days, rather than 37.5 hours over five days.
Atom Bank is set to introduce four day working weeks for its 430 staff members, without decreasing pay.
Employees will have the option to not work either Monday or Friday, and will work 34 hours over the four days, rather than 37.5 hours over five days.
Mark Mullen, chief executive of Atom Bank, said: "Before COVID, the conventional wisdom was you had to commute in, sit at a desk all day and repeat that process when you commuted home.
"COVID showed us that it wasn't necessary. I think doing 9-5, Monday to Friday is a pretty old fashioned way of working.
"Everyone is expected to stick to the new way of working. I can't be sending my staff emails on a Friday, I can't expect to them to respond to them."