# Horizontal Line in footer which ignores the margin

How can I add a horizontal line in the footer which spans the entire width of the page?

\renewcommand{\footrulewidth}{0.4pt}


is giving a line which is inside the margin only.

You need to update the \footrule macro provided by fancyhdr. Here's a possible way:

\makeatletter
\def\footrule{{\if@fancyplain\let\footrulewidth\plainfootrulewidth\fi
\vskip-\footruleskip\vskip-\footrulewidth
\leavevmode\rlap{\hspace*{-2in}\rule{2\paperwidth}{\footrulewidth}}
\vskip\footruleskip}}
\makeatother


In a regular document, this should jump left (negative \hspace) far enough to land outside the page border, then set a horizontal \rule of width \footrulewidth that is twice the width of the paper (ensuring it spans across the entire page).

Here's a working example showing a regular page and the updated footer rule on page 2 (the above change is done mid-document, but you'll want to add it to your preamble for a global effect on your document):

\documentclass{article}
\usepackage{fancyhdr}% http://ctan.org/pkg/fancyhdr
\pagestyle{fancy}
\renewcommand{\footrulewidth}{.4pt}
\begin{document}
Stuff

\clearpage

\makeatletter
\def\footrule{{\if@fancyplain\let\footrulewidth\plainfootrulewidth\fi
\vskip-\footruleskip\vskip-\footrulewidth
\leavevmode\rlap{\hspace*{-2in}\rule{2\paperwidth}{\footrulewidth}}
\vskip\footruleskip}}
\makeatother

Stuff
\end{document}