Carrying in addition (also called addition with regrouping) is the method used to add multi-digit numbers when the sum of a column reaches 10 or more and a unit must be carried over to the next column. It's the standard column-addition method taught in elementary school, usually starting around 2nd or 3rd grade.
How to add in columns with carrying
To add two numbers with this method, always follow the same order:
- Line up the numbers by place value: ones under ones, tens under tens, hundreds under hundreds.
- Start adding from the rightmost column (the ones).
- If that column's result is less than 10, write it down and move to the next column.
- If the result is 10 or more, write only the ones digit of the result and carry 1 to the tens column, adding it together with the other numbers in that column.
- Repeat the same process for each column, from right to left, until you're done.
Why we "carry" a unit
Every time a column adds up to 10 or more, a new group of the next higher unit is actually being formed: 10 ones make 1 ten, 10 tens make 1 hundred, and so on. Carrying 1 isn't a trick, it's regrouping ten small units into a single one of the next order. That's why this method is also called "addition with regrouping": kids are really reorganizing quantities, not memorizing a mechanical step.
