Basic Calculator
Add, subtract, multiply, divide, find powers or remainders, and calculate percentages with signed decimal numbers.
How to use the basic calculator calculator
- Choose the calculator mode. Use Standard for everyday arithmetic or Scientific for roots, powers, logarithms, and trigonometry.
- Enter the expression. Use the on-screen keypad or a supported keyboard key, and check the expression shown above the result.
- Review the displayed result. Domain errors such as division by zero or an invalid real-number root are reported instead of silently returning a misleading value.
- Check important work independently. Finite-precision arithmetic can introduce small rounding differences.
Key inputs covered: First number, Operation, Second number, Maximum decimal places.
Result coverage: The basic calculator calculator reports 5 separate quantities so the primary estimate and its supporting purchase or planning values can be checked together.
Complete everyday arithmetic calculations
Enter positive or negative decimal numbers, choose an operation, and see the result, expression, absolute value, rounded integer, and scientific notation.
Arithmetic and powers
Add, subtract, multiply, divide, raise one number to a power, or find a remainder. Invalid division by zero and non-real powers are rejected before calculation.
Percentages and percentage change
Percentage-of finds the selected percent of a second number. Percentage change compares an ending number with a nonzero starting number.
How the estimate works
The selected arithmetic operation is applied to the first and second signed numbers. Percentage-of uses first ÷ 100 × second; percentage change uses (second − first) ÷ |first| × 100.
With 12 as the first number and 8 as the second number, addition returns 20, subtraction returns 4, and multiplication returns 96.
Assumptions, rounding, and limitations
Inputs are evaluated as real numbers using finite-precision floating-point arithmetic. Displayed results follow the selected precision, while invalid real-number domains are rejected before calculation.
- Division and modulo require a nonzero second number, and percentage change requires a nonzero starting number.
- Displayed digits are rounded for readability; the calculation uses JavaScript double-precision floating-point arithmetic.
- Very large integers and repeating decimals may not be represented exactly because binary floating-point has finite precision.
Sources and review
These references support mathematical definitions and numeric conventions used by the calculator.
Last reviewed: 2026-10-09
Editorial process
BuildPlanCalc publishes the formula, editable assumptions, limitations, and supporting references so the estimate can be checked rather than treated as a black box. See the calculation and review methodology, or report a correction.
Frequently asked questions
Can the basic calculator use negative numbers?
Yes. Both inputs accept positive or negative decimal numbers.
How is percentage change calculated?
It subtracts the starting value from the ending value, divides by the absolute starting value, and multiplies by 100.
Why can some decimal results have rounding differences?
Computers represent most decimals with finite binary floating-point values. The calculator rounds the displayed result to your selected precision.