How to Number Only Some Equations in align Environment
When writing multi-line derivations in LaTeX, you often want to number only the final result or key steps — not every intermediate line. The align environment numbers every line by default, but you can suppress numbering selectively with \nonumber or \notag. Bibby AI shows equation numbers live in the preview panel, so you can instantly verify which lines are numbered without recompiling like you would in Overleaf.
Suppress Numbering with \nonumber
Place \nonumber (or equivalently \notag) before the \\\\ on any line you don't want numbered:
\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align}
f(x) &= (x+1)^2 \nonumber \\
&= x^2 + 2x + 1 \nonumber \\
&= (x+1)(x+1) \label{eq:expanded}
\end{align}
Only Equation~\eqref{eq:expanded} is numbered.
\end{document}Custom Tags with \tag
Use \tag{} to assign a custom label like a star, name, or letter instead of the automatic number:
\begin{align}
E &= mc^2 \tag{Einstein} \\
F &= ma \tag{Newton} \\
E &= h\nu \tag{$\star$}
\end{align}Mix align and align* for Full Control
Alternatively, use align* (no numbering) and add \tag or \numberthis to specific lines you want numbered:
\usepackage{mathtools}
\begin{align*}
x + y &= z \\
2x + y &= 3z \numberthis \label{eq:key} \\
3x + 2y &= 5z
\end{align*}
Only the middle equation (\ref{eq:key}) has a number.💡 Tips
- •\nonumber and \notag are functionally identical — use whichever reads more naturally to you.
- •Always pair \label{} with numbered equations and use \eqref{} to reference them (adds parentheses automatically).
- •Loading mathtools gives you \numberthis, which is the inverse of \nonumber — it adds a number inside align*.
- •Bibby AI's equation panel lists all labeled equations in your document, making cross-referencing instant.
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