The two researchers, one a university lecture and the other a former lecturer, said that the study was carried out on 1,500 first year high school students, when the pupils are on average 15 years old, in an unnamed central Sweden municipality.
"Far too many students have very poor knowledge when it comes to simple competencies like adding and multiplying basic fractions or figuring out percentage calculations," they wrote in an opinion piece in the Dagens Nyheter newspaper on Thursday.
They added that it seemed some Swedish pupils ground to a halt in math class after sixth grade.
"Understanding simple calculations is roughly the same in the eighth-grade as in the sixth," the wrote. "Even during the first year of high school, half of the students had problems with basic calculations that they should have learned in middle school."
The researchers argued that this slow down in math skills probably meant that the student simply did not understand what they were being asked to learn in earlier grades.
"It's remarkable. It makes you wonder how it's possible that a pupil can go year after year lacking basic maths skills without the teachers reacting."
Here are some of the questions from the testing process, followed by how many of the 1,500 students answered incorrectly.
7x8+5 (38 percent answered incorrectly)
What's 15 percent off a 720 kronor item? (54 percent were wrong)
Divide 0.16 by 4 (50 percent wrong)
Add four fifths and two thirds (44 percent wrong)