Sales increased by 41 percent during the week, Monday to Friday, compared to last year.
In just Friday, sales increased by 16 percent.
Klarna handles about half of all online purchases in Sweden.
"We have seen a large increase in e-commerce throughout the week and this year's Black Friday was the biggest e-commerce day ever," says Viveka Söderbäck, consumer expert at Klarna, according to a press release.
Habits change
Previously, Friday was the biggest shopping day, but customers' habits have begun to change and shopping is now spread out more over several days, according to Klarna.
The products that increase the most compared to a normal day are electronics, children's products and entertainment. It is among people aged 66-75 that online shopping has increased the most compared to last year.