Add a rule after chapter title using titlesec

Question

I've been experimenting with chapter title formatting using titlesec but I can't seem to find the proper way to add a rule just below the chapter title. After reading the doc, I found that \titleline does that, but I'm not sure where in the \titleformat syntax to place it.

Answer 1

Here's one possible solution using the last optional argument for \titleformat to insert some vertical spacing and the rule:

\documentclass{book}
\usepackage{titlesec}

\titleformat{\chapter}[display]
{\normalfont\huge\bfseries}{\chaptertitlename\ \thechapter}{20pt}{\Huge}[\vspace{2ex}\titlerule]

\begin{document}

\chapter{Test Chapter}

\end{document}