Changing a blank space to Appendix A/B/... in the Table of Contents

The code in the preamble of your document is quite convoluted. To the extent that I understood what's going on, it appears that various instructions contradict or override each other. My two main suggestions, which together let you achieve your stated formatting objective, are

• Don't execute \backmatter, at least not before the appendices.

• Repeat the \titlecontents macro after \begin{appendices}, but now with Appendix as the hard-coded prefix string.

If you don't need the "Appendices" line in the ToC, omit the toc option while loading the appendices package.

\documentclass[11pt,openany,twoside]{book} \raggedbottom \let\cleardoublepage\clearpage \usepackage[a4paper]{geometry} \usepackage{parskip} \usepackage{amsmath} %%\usepackage{amsfonts} % is loaded automatically by amssymb \usepackage{amssymb} \usepackage{amsthm} \usepackage{array} \usepackage[table]{xcolor} % note 'table' option (for 'colortbl') \usepackage{graphicx} \usepackage[dotinlabels]{titletoc} \usepackage{background} \backgroundsetup{contents={}} \usepackage{helvet} %%%\usepackage{color} % don't load both xcolor and color \usepackage{fancyhdr} \usepackage{hhline} \pagestyle{fancy} \usepackage{booktabs} \usepackage[noindentafter,calcwidth]{titlesec} \titleformat{\section}% {\normalfont\Large\bfseries\color{black}} {\thesection}{1em}{} \titleformat{\subsection}% {\normalfont\large\bfseries\color{black}} {\thesubsection}{1em}{} \usepackage{calc,pifont} \usepackage{longtable} \usepackage{multirow} %%%\usepackage{colortbl} % don't load colortbl independently of xcolor \newcommand*\myheaderfooterfont{\normalfont\bfseries} \makeatletter \renewcommand\@biblabel[1]{\textsuperscript{#1}} \makeatother \usepackage[nottoc]{tocbibind} \usepackage{verbatim} % are you sure you need this package? \usepackage[ragged]{sidecap} \usepackage{caption} \captionsetup[table]{skip=5pt} \usepackage[marginal]{footmisc} \renewcommand\footnoterule{\vspace*{-3pt}% \hrule width 2in height 1.4pt \vspace*{2.6pt}} \setlength\footnotemargin{10pt} \usepackage{tocloft} \renewcommand{\cfttoctitlefont}{\hfill\normalfont\bfseries\huge} \renewcommand{\cftloftitlefont}{\hfill\normalfont\bfseries\huge} \renewcommand{\cftlottitlefont}{\hfill\normalfont\bfseries\huge} \setlength{\cftbeforetoctitleskip}{-.3cm} \setlength{\cftbeforeloftitleskip}{-.3cm} \setlength{\cftbeforelottitleskip}{-.3cm} \setlength{\cftafterloftitleskip}{1.7cm} \setlength{\cftaftertoctitleskip}{1.4cm} \setlength{\cftafterlottitleskip}{1.7cm} \renewcommand{\cftchapfont}{\normalfont\bfseries} \renewcommand{\cftsecfont}{\normalfont} \renewcommand{\cftsubsecfont}{\normalfont} \renewcommand{\cftchapafterpnum}{\vskip-4pt} \usepackage{etoolbox} \usepackage{regexpatch} \usepackage{listings} \usepackage{float} \captionsetup[table]{labelsep=period, indention=45pt, justification=raggedright} \makeatletter \pretocmd{\chapter}{\addtocontents{toc}{\protect\addvspace{-4\p@}}}{}{} \makeatother \usepackage{hyperref} \hypersetup{ colorlinks=true, linkcolor=blue, } \usepackage[toc,header]{appendix} \begin{document} \frontmatter { \hypersetup{linkcolor=black} \sffamily \tableofcontents } \titlecontents{chapter}[7pc] {\addvspace{1pc}\normalfont\bfseries \filright} {\contentslabel [Chapter \thecontentslabel]{7pc}} {}{\hfill\contentspage} [\addvspace{2pt}] \mainmatter \chapter{XYZ} rhrrgrrgryryryfyfyfr \chapter{ABC} dgdegegegegeggdddrr \begin{appendices} %\addtocontents{toc}{\protect\renewcommand{\protect\cftchappresnum}{Appendix }} %% Rerun the \titlecontents macro, but now with 'Appendix' prefix string \titlecontents{chapter}[7pc] {\addvspace{1pc}\normalfont\bfseries \filright} {\contentslabel [Appendix \thecontentslabel]{7pc}} {}{\hfill\contentspage} [\addvspace{2pt}] \chapter{Derivation of X} The contents\dots \chapter{Derivation of Y} \end{appendices} \end{document}