documentclass{article}
usepackage[utf8]{inputenc}
usepackage{booktabs}
usepackage{siunitx}

begin{document}

section{Introduction}

begin{table}[]
begin{tabular*}{textwidth}{@{extracolsep{fill}}c l r l r l r l r}
midrule
  textbf{År} &
  multicolumn{2}{c}{textbf{Avdrag}} &
  multicolumn{2}{c}{textbf{Renter}} &
  multicolumn{2}{c}{textbf{Terminbeløp}} &
  multicolumn{2}{c}{textbf{Restlån}} \
midrule
  2018 & kr & num{17446} & kr & num{6000} & kr & num{23446} & kr & num{182554} \
  2019 & kr & num{17969} & kr & num{5477} & kr & num{23446} & kr & num{164585}  \
  2020 & kr & num{18508} & kr & num{6000} & kr & num{23446} & kr & num{146076}  \
  2921 & kr & num{17446} & kr & num{6000} & kr & num{23446} & kr & num{127012}  \
  2022 & kr & num{17446} & kr & num{6000} & kr & num{23446} & kr & num{107377}  \
  2023 & kr &             & kr & num{6000} & kr & num{23446} & kr & num{}  \
  2024 & kr & num{20953} & kr & num{6000} & kr & num{23446} & kr & num{}  \
  2025 & kr & num{21}    & kr & num{6000} & kr & num{23446} & kr & num{44864}  \
bottomrule
end{tabular*}
end{table}

end{document}