What does this calculator do?
Column addition and subtraction organize numbers by place value. This combined calculator shows the aligned magnitudes and explains each carry or borrow. Signed inputs may turn a subtraction into magnitude addition, or an addition into magnitude subtraction.
For a general expression use the Scientific Calculator; for fractions use the Fraction Calculator.
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Optional place value learning blocks (paid link) can make regrouping tangible. No purchase is required.
How to enter numbers and read the columns
Choose Addition or Subtraction, enter both numbers and select Calculate. The top row of the magnitude working may be reordered for subtraction so that a smaller magnitude is subtracted from a larger one. The final step restores the sign for the original request.
Results start blank, clear after edits, and reappear only after a valid calculation. Reset clears both numbers and restores the default operation. Copy, Download and Print include the calculation steps and column working.
Optional squared exercise notebooks (paid link) can help keep handwritten digits aligned.
Exact method and place value
Append fractional zeros until both numbers have the same decimal scale, then use signed-integer addition. Equal signs require magnitude addition; unequal signs require magnitude subtraction. In addition, each column includes its incoming carry. In subtraction, subtract an incoming borrow and, if necessary, add 10 while borrowing 1 from the next column.
All supported operations use integer arithmetic and decimal scaling; the tool does not evaluate user-supplied JavaScript or silently approximate an unsupported input.
Worked examples
For 48 + 27, 8 + 7 = 15: write 5 and carry 1; 4 + 2 + 1 = 7, giving 75. For 1000 - 1, borrowing propagates through the zero columns to give 999. For 3.2 - 5.45, compare aligned magnitudes 3.20 and 5.45: 5.45 - 3.20 = 2.25, then restore the negative sign to get -2.25. For -3 - (-5), the result is 2.
Understand carries, borrowing and signs
The Carry in row indicates an extra 1 added at that column. The Borrow in row indicates 1 to subtract at that column because it lent to the column on its right. Individual steps explain any additional 10 received. The column display shows a nonnegative magnitude, while the large result gives the signed answer.
Optional place value charts (paid link) can support place-value practice. For digit-by-digit division, use the existing Long Division Calculator.
Accuracy and supported input limits
Use at most 20 entered digits per number and at most 10 fractional digits. Leading zeros count toward the input limit. A leading + or - and forms such as .5 or 5. are accepted. Empty entries, commas, fractions, exponent notation and arbitrary expressions are unsupported. Very long working scrolls horizontally inside its own box; steps may be lengthy. These tools teach base-ten arithmetic, not significant-figure or measurement-uncertainty rules.
Optional arithmetic workbooks (paid link) can provide extra exercises. The Rounding Calculator handles rounding as a separate task.
Long Addition & Subtraction Calculator FAQs
Yes. Each input supports at most 20 entered digits in total, including at most 10 digits after the decimal point. Use a decimal dot, without grouping commas.
Yes. The column layout works with magnitudes; the steps explain the signs and the main answer is the signed result of the original operation.
No. These supported finite-decimal operations use exact integer arithmetic and decimal scaling. Trailing fractional zeros are removed.
The steps follow the entered digits, carries or borrows, and the selected operation. Longer inputs need more working.
No. Use ordinary whole numbers or finite decimals. Expressions, fractions, exponent notation and thousands separators are rejected.
The arithmetic runs in your browser. Copy, Download and Print are optional result actions. Changing an input clears the previous answer.
Sources and methodology
Independently implemented exact base-ten arithmetic, reviewed October 30, 2026. Column working explains place value. Sources describe the mathematics; the linked organizations do not endorse this calculator.