LaTeX Superscript & Subscript

The two-second answer

% Single character
$x^2$       % superscript: x squared
$x_i$       % subscript: x sub i

% Multiple characters — use braces
$x^{n+1}$   % superscript with multi-char
$x_{i,j}$   % subscript with multi-char

% Both at once
$x_i^2$     % x sub i, squared

% Nested
$e^{x^2}$   % e to the (x squared)

The rules

1. Must be in math mode. Wrap inline math with $...$ or use a display environment like \[ ... \], equation, or align.
2. Single-token shortcut. Without braces, only the next single token is super/subscripted. x^n+1 means (xn) + 1, not xn+1. Use braces: x^{n+1}.
3. Order doesn't matter. x_i^2 and x^2_i typeset identically. Most style guides prefer subscript first.
4. Outside math mode, use \textsuperscript{...} and \textsubscript{...}. Example: 1\textsuperscript{st} → 1^st.

Common patterns

Powers and exponents

$x^2$        % x squared
$x^3$        % x cubed
$x^{10}$     % x to the 10
$x^{n+1}$    % x to the n+1
$2^{32}$     % 2 to the 32
$e^{i\pi}$   % e to the i pi

Indexed variables

$a_1, a_2, \ldots, a_n$    % indexed sequence
$x_{ij}$                  % matrix element
$\sum_{i=1}^{n} x_i$      % indexed sum

Combined sub and superscript

$T_n^k$                    % stirling-style notation
$\binom{n}{k}$             % preferred binomial
$\sigma_x^2$               % variance
$\hat{\theta}_{\text{MLE}}$  % MLE estimator

Chemistry (text-mode subscripts)

H\textsubscript{2}O          % H2O — works
% Better with mhchem package:
\usepackage{mhchem}
\ce{H2O}                     % gets full chemical formatting
\ce{H2SO4}                   % sulfuric acid
\ce{Na+}                     % cation

Ordinals (text mode)

1\textsuperscript{st}        % 1st
21\textsuperscript{st}       % 21st
2\textsuperscript{nd}        % 2nd
N\textsuperscript{th}        % Nth

Common errors

"Missing $ inserted"

You forgot math mode. x^2 in plain text fails. Fix: $x^2$.

"Double superscript" / "Double subscript"

You wrote x^2^3 or x_i_j without braces. LaTeX can't tell what you mean. Fix: brace one of them, e.g. x^{2^3} or x_{i_j}.

Only one character is superscripted

You wrote x^n+1. Only n is in the superscript. Fix: x^{n+1}.