# How to add a footnote to an equation number?

I would like to add a footnote to an equation number. For example, it should look like:

(This figure is taken from MS word.)

Does anyone know how to do this in latex? I have tried the following code:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
$$\label{eq1}\refstepcounter{equation} a=b \tag*{(\theequation)\protect\footnotemark}$$
\footnotetext{A footnote}

Equation \ref{eq1} is a good equation.

\end{document}


But each time the equation is referenced, a new superscript will appear like:

(This is from latex.)

When the equation is referenced, a new superscript shows up. How to avoid it?

• But why do you want to add the foot note to the tag, instead of at the end of the formula? – Bernard Jan 15 '16 at 23:51
• If adding a footnote at the end of the formula, it is confusing because the superscript of the footnote is similar to a symbol in the equation. – FengWang Jan 15 '16 at 23:55
• In such a case, I would write at the end of the formula something like \quad\footnotemark. – Bernard Jan 16 '16 at 0:04

Here is a solution, with the \newtagform, usetagform commands from mathtools. However, you can't use \eqref nor \cref for equations with footnotes.

\documentclass{article}
\usepackage{mathtools}
\newtagform{fn}{(}{)\footnotemark}

\begin{document}

\usetagform{fn}
$$\label{eq1} a=b$$
\footnotetext{Some text. }
Equation (\ref{eq1}) is a good equation.
\usetagform{default}
$$\label{eq2} c = d$$

\end{document}