The “missing $ inserted” LaTeX error means you used a character that only works inside math mode, but you used it in regular text. LaTeX is telling you it tried to insert a $ to enter math mode because it had no other way to process the character. The fix is almost always escaping a special character or removing an invisible character from copy-paste.
What you see:
! Missing $ inserted.
$
l.27 The growth rate was 15%
of the baseline.
Quick answer
Check the line number in the error for any of these characters used without a backslash:
_(underscore) – write\_in text, or wrap in$...$for subscripts^(caret) – write\^{}in text, or wrap in$...$for superscripts%(percent) – write\%(without the backslash, LaTeX treats it as a comment)&(ampersand) – write\&#(hash) – write\#
If the line looks correct, delete it and retype it manually. The cause is an invisible Unicode character from copy-paste.
The 10 Reserved Characters in LaTeX
LaTeX reserves 10 characters for special purposes. Using any of them in regular text without escaping produces an error. Here is the complete list with the correct way to type each one:
_ → \_ ^ → \^{} % → \% & → \& # → \# $ → \$ { → \{ } → \} ~ → \textasciitilde{} \ → \textbackslash{}
The underscore and percent sign cause the most errors because they appear naturally in filenames, URLs, and scientific text.
Underscores in Filenames and Paths
This catches people constantly. \includegraphics{my_figure.pdf} fails because LaTeX interprets the underscore as a subscript command. The same happens in \bibliography{my_refs} and \input{chapter_1}.
The fix: escape the underscore (\includegraphics{my\_figure.pdf}) or rename the file to remove underscores (myfigure.pdf). Renaming is cleaner because it avoids the issue everywhere the filename is referenced.
Percent Signs Eaten as Comments
This one is especially confusing because the error message does not mention comments. When you write 15%, LaTeX treats everything after the % as a comment. The rest of the line disappears. The next line then starts in an unexpected state, which often triggers “missing $ inserted” because LaTeX is now in the middle of a broken command.
The fix: 15\%. Always escape percent signs in text.
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Characters Pasted From Word or the Web
If the error appears on a line that looks perfectly correct, the problem is an invisible character from copy-paste. Word, Google Docs, and websites insert characters that look identical to their LaTeX equivalents but are different bytes.
Smart quotes (\u201C \u201D instead of ") cause LaTeX to misinterpret the line. Delete and retype using `` for opening and '' for closing quotes.
The degree symbol (\u00B0) pasted from Word triggers math mode errors. Use \textdegree{} from the textcomp package, or $^\circ$.
Em dashes and en dashes (\u2014 and \u2013) pasted as Unicode can cause unexpected errors. Delete and retype as --- for em dash and -- for en dash.
The micro sign (\u00B5) and other Unicode symbols from scientific text break pdflatex. Use the LaTeX command instead ($\mu$), or add \usepackage[utf8]{inputenc} to your preamble.
For other common LaTeX errors, see our complete guide to LaTeX compilation errors. If your error is specifically about fonts in the final PDF, see our font not embedded fix guide.
Frequently Asked Questions
It means LaTeX found a character that only works inside math mode (like _ for subscript or ^ for superscript) but you used it in regular text. LaTeX tried to fix the problem by inserting a $ to enter math mode, which usually causes a cascade of additional errors. The fix is to escape the character with a backslash (e.g., \_ instead of _) or delete and retype the line if the cause is an invisible Unicode character from copy-paste.
In LaTeX, the percent sign % is reserved as the comment character. Everything after % on a line is ignored by the compiler. To print a literal percent sign in your document, write \%. This is one of the 10 reserved characters in LaTeX that must be escaped with a backslash when used in text.
Escape the underscore with a backslash: \includegraphics{my\_figure.pdf}. Or rename the file to remove underscores entirely (myfigure.pdf), which is the cleaner solution because it avoids the escaping issue everywhere the filename appears in your document.
