Subtracting within 100
In 2nd grade, children learn to subtract numbers within 100, such as 82 - 56, by counting up, taking numbers apart into tens and ones, and using what they know about adding.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our 2nd grade practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
A baker made 75 cookies. If 20 cookies were sold, how many cookies are left?
- 95
- 55
- 65
Why this matters
Subtracting is how your child works out how many are left and how much more, and getting comfortable with it makes everyday math feel easier. It leads to subtracting within 1,000 later this year, then to multi-step problems, time, and money in 3rd grade. It also gives your child a way to check their own work, since adding the answer back should lead to where they started. You'll see it when you count change or find out how many pages are left.
If subtracting feels shaky, your child can review adding within 100, since the two work together.
Where kids can get stuck
- Subtracting the smaller digit from the larger in each place, so 82 - 56 becomes 34.
- Counting back one number at a time and losing track partway, so 53 - 18 ends up a few away from 35.
- Thinking subtraction only means taking away, so a question like "How many more is 64 than 48?" feels like a different kind of problem.
How you can help
- Count change together. If something costs 63 cents and you hand over a dollar, ask how much change should come back, and have your child count up from 63 to 100.
- Ask how many pages are left. If your child is on page 64 of a 90-page book, have them count up from 64 to 90, then check by adding the two parts back together.
- Compare scores after a game. If you have 83 points and your child has 59, ask how many more points you have, and how they know.
Want a little more? Watch the kid-friendly video below together, or try Bobby's Math Club for free practice that adapts to your child.
Kid-friendly explanation
Questions parents ask
Why does my child count up to subtract?
Subtraction can mean finding how far apart two numbers are. For 82 - 76, counting up is quicker than taking away: 4 gets you from 76 to 80, and 2 more gets you to 82, so the answer is 6. It is a real strategy, and it shows your child how adding and subtracting fit together.
Should I teach my child to borrow?
Borrowing is a shortcut for trading one ten for ten ones, so it is best to follow what your child's school is teaching. If your child already borrows, ask them to show what it means: for 82 - 56, 8 tens and 2 ones becomes 7 tens and 12 ones. Understanding the trade matters more than the method.
What if my child can add within 100 but finds subtracting harder?
That's common, and it isn't your fault or your child's. Subtracting is its own skill, because it asks children to think about taking numbers apart and how far apart two numbers are. Keep the numbers friendly at first, and have your child check each answer by adding it back.
Make learning math fun
Bobby's Math Club turns 2nd grade math practice into something fun to do together.
- Unlimited practice, completely free
- A few minutes a day, at just the right level
- You see their progress and what to work on next
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
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Join the clubNote for teachers: This skill is covered by Common Core math standard 2.NBT.B.5: “Fluently add and subtract within 100 using strategies based on place value, properties of operations, and/or the relationship between addition and subtraction.” Learn how Bobby's Math Club can help your students grow. (Common Core 2.NBT.5)