Btukfyl

I'm trying to keep body text inside its box but it overlaps the header. I tried using voffset, headsep and headheight, but it seems they do not work as I expect

documentclass{article}

usepackage[utf8]{inputenc}

usepackage{showframe,blindtext,fontawesome} 

usepackage{fancyhdr}

usepackage[a4paper, nomarginpar,margin=1in]{geometry}

pagestyle{fancy}

rhead{

    {

        fontsize{40pt}{60pt}selectfont

        Foo Bar\

    }

    555faPhone\

    555faPhone\

    555faPhone\

noindentmakebox[linewidth]{rule{linewidth}{0.4pt}}

}

begin{document}

blindtext

end{document}

Please have a look into the logfile of your code. There you find:

Package Fancyhdr Warning: headheight is too small (12.0pt): 

 Make it at least 80.59785pt.

That means you have to add an command to enlarge the headheight to 81pt:

setlength{headheight}{81pt}

With the following MWE

documentclass[a4paper]{article}

usepackage[utf8]{inputenc}

usepackage{blindtext,fontawesome} 

usepackage{fancyhdr}

usepackage[showframe, nomarginpar,margin=1in]{geometry}

pagestyle{fancy}

rhead{

    {

        fontsize{40pt}{60pt}selectfont

        Foo Bar\

    }

    555faPhone\

    555faPhone\

    555faPhone\

noindentmakebox[linewidth]{rule{linewidth}{0.4pt}}

}

setlength{headheight}{81pt} % <=======================================



begin{document}

blindtext

end{document}

you get the result:

Your header is too tall and fancyhdr warns you about this:

Package Fancyhdr Warning: headheight is too small (12.0pt): 

 Make it at least 80.59785pt.

 We now make it that large for the rest of the document.

 This may cause the page layout to be inconsistent, however.

The important part here is that you'll see the header fitting better from page two onward.

Below is a similar example with an oversized image requiring at least 63.60004pt; setting headheight to 65pt is sufficient:

documentclass{article}

usepackage{fancyhdr,graphicx,blindtext}

usepackage{geometry}

geometry{

  margin = 1in, % Set all margins to 1in

  headheight = 65pt, % Update header height to accommodate for large content

  tmargin = dimexpr1in+65pt % Update top margin to accommodate for large header content

}



rhead{includegraphics[height=5baselineskip]{example-image}}% Something big

pagestyle{fancy}



begin{document}



blindtext[50]



end{document}