How to use this calculator

When adding decimal numbers, align the decimal points before adding each place-value column. This tool performs the calculation with scaled whole numbers rather than binary floating-point addition. It is useful when a familiar sum such as 0.1 + 0.2 must be displayed exactly as 0.3.

The method

Sum = decimal_1 + decimal_2 + ... + decimal_n

Enter the values in the labeled fields, check the units or selected mode, and choose Calculate. The result includes the applicable working and a breakdown or visual when useful. Change an input and calculate again to update the result.

WORKED EXAMPLE

Decimal numbers to add: 12.35; 0.7; -2.05

Exact decimal sum: 11.00

Decimal-safe addition without binary rounding artifacts.

Scope and limitations

Supports plain decimal notation, including negative numbers. Fractions, exponent notation, currency symbols, and thousands separators are not accepted in this tool.

Common questions

Why do the values have trailing zeros in the table?

The tool aligns all values to the largest number of decimal places in your input. Those trailing zeros do not change their values.

Can I subtract by entering a negative number?

Yes. Adding -2 is equivalent to subtracting 2.

References & further reading

External references provide background, not an endorsement of this implementation. See our methodology for numerical conventions and limitations.