Prior to 1877, the name was spelled "Frederiksstad", then from 1877–1888 it was written as "Fredriksstad", and finally since 1889 it has been spelled in its current form: "Fredrikstad".
До 1877 название города имело написание "Frederiksstad", в период с 1877 по 1888 годы — "Fredriksstad", после 1889 года современное написание "Fredrikstad".