There are several calculators for Emacs out there. Here is a selection of modes for you to use if you need some calculations.

- PlainLispForMath describes how to write and evaluate simple arithmetic lisp expressions. This requires you to use lisp prefix notation. Example: (+ 1 3) ⇒ 4
- The SimpleCalculator is a little pocket calculator featuring various trigonometric functions, binary/octal/hexadecimal modes for input & display, etc. Expressions are entered using normal infix notation, parens are used as normal. Example: (1 + 3) ⇒ 4
- There is also a SimpleRpnCalculator available.
- AdvancedDeskCalculator is a very powerful package featuring RPN, arbitrary precision (floating point), complex numbers, error forms, vectors, matrices, dates, times, an interface to gnuplot, and symbolic calculus. Also known as GNU Calc.
- AbacusMode simulates a traditional Abacus for all your Math requirements.
- CalculationPad is a simple functional language that runs on Emacs buffer.

Other miscellaneous math related things:

- SpreadSheet – using Emacs as a spreadsheet calculator (like Lotus/Excel)
- ElectricFormMode – a minor mode for light computation in a buffer, like summing up columns of numbers
- AddNumbers helps you sum a column of numbers.
- See also RectangleAdd.

- LoanPaymentCalculator does what it says… calculates loan payments.
- ComputerAlgebraSystems – a list of external programs with Emacs interfaces
- MatrixOperations – EmacsLisp code to help you use multi-dimensional arrays and do matrix ops on them
- AddCommasToNumbers – format decimal numbers with properly placed commas