Four columns: thousands, hundreds, tens, ones. Line them up, one digit per square, and start from the ones as always. The rule does not change with the size.
Step 1: Let's Learn
Read it, or press Listen and follow the words.
Try it first
Add 348 and 276 in columns. What is the total?
Stuck is fine. Let’s Learn shows the way next. Got it first time? You can jump ahead to Watch an Example.
Carry after carry
2,648 + 1,975. Ones: 8 + 5 = 13, write 3 carry 1. Tens: 4 + 7 + 1 = 12, write 2 carry 1. Hundreds: 6 + 9 + 1 = 16, write 6 carry 1. Thousands: 2 + 1 + 1 = 4. The answer is 4,623.
A carry past the front
7,859 + 4,386. The thousands make 7 + 4 + 1 = 12. There is no column to the left, so write both digits: 12. The answer is 12,245, a five-digit number.
The comma
A comma every three digits from the right makes 12,245 readable. It does not change the columns; write the digits one per square and add the comma when you read the answer.
Estimate to check
2,648 + 1,975 is about 2,600 + 2,000 = 4,600. 7,859 + 4,386 is about 8,000 + 4,000 = 12,000. An answer far from the estimate means a column slipped.
Step 2: Try It Yourself
Press Next step. Three carries, then a fourth column.
2648+1975
Step 0 of 4
2,648 + 1,975 = …
11117859+438612245
7,859 + 4,386 = 12,245
- 1Ones: 9 + 6 = 15. Write 5, carry 1 to the tens.
- 2Tens: 5 + 8 + the carried 1 = 14. Write 4, carry 1 to the hundreds.
- 3Hundreds: 8 + 3 + the carried 1 = 12. Write 2, carry 1 to the thousands.
- 4Thousands: 7 + 4 + the carried 1 = 12. Write 2, carry 1 to the ten thousands.
- 5Ten thousands: only the carried 1. Write 1. 7,859 + 4,386 = 12,245.
Step 3: In Real Life
A town’s two schools
One school has 2,648 pupils, the other 1,975. The council adds them in columns: 8 + 5 = 13, 4 + 7 + 1 = 12, 6 + 9 + 1 = 16, 2 + 1 + 1 = 4. 4,623 pupils, carried three times.
Step 4: Watch an Example
One step at a time.
Watch Ana Add 2,847 and 4,596
Ana estimates first: about 3,000 and 5,000 make around 8,000. Then she adds on the board. Press Next step to watch each move.
2847+4596
Step 0 of 4
2,847 + 4,596 = …
Watch Leo Add 6,738 and 5,684
Leo estimates first: about 7,000 and 6,000 make around 13,000. He leaves a spare square on the left. Watch what he writes when the thousands make 12.
6738+5684
Step 0 of 5
6,738 + 5,684 = …
Step 5: Your Turn
Practice makes it stick.
The Stadium
Problem 1 of 11
A stadium has 4,568 seats below and 2,796 above. How many seats?
4568+2796
Add the ones: 8 + 6. Write the ones digit.
Square 1 of 7
4,568 + 2,796 = …
The Bike Fund
Problem 2 of 11
A club had $8,675 saved and raised $3,948 more. How much now?
8675+3948
Add the ones: 5 + 8. Write the ones digit.
Square 1 of 9
8,675 + 3,948 = …
Four Columns
Estimate first. Then write each one out on the board.
Problem 3 of 11
3,241 + 2,536 = ?
3241+2536
Add the ones: 1 + 6. Write the ones digit.
Square 1 of 4
3,241 + 2,536 = …
Problem 4 of 11
4,628 + 3,594 = ?
4628+3594
Add the ones: 8 + 4. Write the ones digit.
Square 1 of 7
4,628 + 3,594 = …
Problem 5 of 11
6,857 + 5,469 = ?
6857+5469
Add the ones: 7 + 9. Write the ones digit.
Square 1 of 9
6,857 + 5,469 = …
Find the Mistake
One line on each page is a slip. Find it, then fix it.
Problem 6 of 11
Dev adds 5,749 and 6,382. One line is a slip. Which?
Dev's page for 5,749 + 6,382
- 1Ones: 9 + 2 = 11. Write 1, carry 1.
- 2Tens: 4 + 8 + 1 = 13. Write 3, carry 1.
- 3Hundreds: 7 + 3 + 1 = 11. Write 1, carry 1.
- AnswerThousands: 5 + 6 + 1 = 12. Write 2. Answer: 2,131
Problem 7 of 11
What is 5,749 + 6,382 really?
5749+6382
Add the ones: 9 + 2. Write the ones digit.
Square 1 of 9
5,749 + 6,382 = …
Problem 8 of 11
Maya adds 4,375 and 2,948. One line is a slip. Which?
Maya's page for 4,375 + 2,948
- 1Ones: 5 + 8 = 13. Write 3, carry 1.
- 2Tens: 7 + 4 + 1 = 12. Write 1, carry 2.
- 3Hundreds: 3 + 9 + 2 = 14. Write 4, carry 1.
- AnswerThousands: 4 + 2 + 1 = 7. Answer: 7,413
Problem 9 of 11
What is 4,375 + 2,948 really?
4375+2948
Add the ones: 5 + 8. Write the ones digit.
Square 1 of 7
4,375 + 2,948 = …
Which Way?
Pick the way that starts right.
Problem 10 of 11
The columns give the digits 1, 0, 6, 3 and 7. Which way writes it?
Problem 11 of 11
Which way tells you fastest whether 7,462 + 8,375 has five digits?
Step 6: Quick Check
Show what you know.
Question 1 of 2
2,648 + 1,975
Question 2 of 2
The thousands column makes 12 and there is no column to the left. What do you write?
Ready for more?Optional. Past the lesson, for anyone who wants it.
Stretch 1 of 2
What must you add to 9,648 to reach five digits? Give the smallest.
Stretch 2 of 2
Without adding, which of these totals must have five digits?
What You Learned
- Four columns, the same rule: ones first.
- Carry in as many columns as needed.
- A carry past the front is the answer’s new first digit.
For the grown-up
This is lesson 1.5 written out. Nothing new happens at four digits except that carries pile up; a child who is unsure should say each column aloud, including the carry, before writing.
Insist on squared paper or a ruled grid. Most four-digit errors are a digit in the wrong column, not a wrong sum.
The slip this lesson targets is the thrown-away front carry: Dev's thousands column makes 12 and only the 2 goes down, so 12,131 comes out as 2,131. Ask what the small 1 counts. It is one ten thousand, and with no column to its left it becomes the answer's first digit. The other slip to watch is Maya's, swapping the two digits of a column total: 12 tens is 2 tens written down and 1 hundred carried, never 1 written down and 2 carried. Saying the total aloud as "twelve tens, so two tens and one hundred" removes both.