Big number calculator

Add, subtract and multiply large decimals exactly, or divide them as a reduced exact fraction.

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Privacy details

Big number calculator processes your input in this browser. Inputs and results are excluded from analytics. Recent tools save tool names, visit counts and last-visit times. Saved tools store only their names. Draft saving is optional and stays on this device; delete saved text with the draft controls. Loading text from a URL is optional and contacts that server; its URL and your IP address are visible to the server. An optional “Use in” action keeps a handoff in this tab. The next tool removes it on arrival and ignores it if more than a minute has passed.

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First decimal

Second decimal

More inputs and assumptions

Operation

Answer

…

Add, subtract and multiply large decimals exactly, or divide them as a reduced exact fraction.

More results

Precision and calculation record

Decimal places in numeric results and text downloads

Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Saved scenario

Save the current answer, then change an input to compare. This clears when you leave.

Formula and assumptions

Whole-number and finite-decimal arithmetic is exact within the stated input limits. Any requested rounding uses the selected setting. Thousands separators such as 1,000 are accepted; use a dot for decimals.

Scratch calculator

Check another calculation

Use +, −, ×, ÷, parentheses and %. A percentage is divided by 100. This does not change the main tool.

Reset reloads the tool with its starting values and releases open files and device controls. Saved drafts stay on this device until you delete them.

Links include your inputs and settings. Anyone with the link can see them, so leave out private text. Files and generated results are left out; random draws run again.

Keyboard shortcuts

Updated 2026-09-20

Using Big number calculator

Add, subtract and multiply large decimals exactly, or divide them as a reduced exact fraction.

Next: Fraction calculator

Next: Decimal to fraction calculator

A worked example

Example inputs: first decimal = 9007199254740993, second decimal = 1, operation = 0. Exact result = 9007199254740994.

Before you use the result

Base-ten digits are converted to bounded integer coefficients. Up to 1,000 input digits and exponents of ±1,000; no binary floating-point rounding. Division retains a fraction rather than silently truncating recurring decimals. Whole-number and finite-decimal arithmetic is exact within the stated input limits. Any requested rounding uses the selected setting.

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ToolOctopus. “Big number calculator.” Updated 2026-09-20. https://tooloctopus.com/big-number-calculator.

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