Subtraction facts can be tricky for students to memorize. That is why subtraction mental math strategies are so important for students. Even if students forget the subtraction fact in the moment, they can use a mental math strategy to find the answer quickly and accurately. 

So I thought I would share 3 subtraction mental math strategies your students need to know. Plus, 2 bonus higher level subtraction mental math strategies at the end. You won’t want to miss out on these one. They turn out to be my students’ favorite strategies!

 

Subtraction Mental Math Strategies

 

Make Ten

Students have worked with the number ten a lot. The number ten is naturally in their lives. They can easily know what numbers make up ten. So it’s easy to subtract from ten. 

Students can use this to solve harder math facts. For example, if a student sees the equation 12-4, they can break apart the 4 into 2 and 2. My 2nd graders know that 12-2=10 and 10-2=8. So they know 12-4 is 8.

It’s important for students to get a lot of practice with this subtraction mental strategy. I like to model for students and let them see it visually with ten frames. We fill in the first number, cross off until we get to ten, and then cross off the rest of the number we are subtracting. This helps students see how to break apart the number to get to ten easily.

Then I have students practice using this mental strategy using task cards. I laminate these task cards so that students can use dry erase markers on them. Then I have them work around the room with a partner. I also hang up an anchor chart showing this strategy so students have plenty of support. It also helps when I walk around the room guiding students.

Then for independent practice I have students do a Subtraction Make Ten worksheet. This helps me see how students are really understanding this strategy. It shows me which students need a little more practice. I will set out other worksheets or task cards as center activities. Find these Subtraction Make Ten task cards and worksheets here.

I like to keep reviewing this strategy with students. It is easy to do this with my Math Fact of The Day warm up activity. First, I display a subtraction math fact. Then I give students some time to think of the answer and how they got to the answer. After that, I have students turn and talk and tell their neighbor how they figured out the answer. I call on a few students to share their reasoning with the class. As students are sharing their reasoning, I’ll write up the numbers and equations they are saying up on the board and as they explain. This makes it so other students can follow along and I can add to their explanation as needed. Find this Math Fact of the Day resource here.

 

Doubles and Near Doubles

We make doubles facts a big deal in my classroom. Whenever we come across a doubles fact in our regular math lesson I get really excited. We have a chant that goes with each doubles fact so I have my students say it with me.

For example, 7+7 is 14, let’s lean! I do this because I want students to get in the habit of recognizing doubles facts and using them to help them with subtraction mental math strategies. For more on teaching doubles facts, read this blog post here: What Are Doubles Facts

If students come across the math equation of 13-6, we can reason through it to find the answer. I would model this to students by saying. “Oh, I know 6+6 is 12, so 6+7 is 13. That means 13-6=7.” After modeling it so many times, students start using the same reasoning.

Students need lots of practice to master this subtraction mental strategy. So I have them get with a partner and solve subtraction facts with the doubles and near doubles strategy together. I walk around the room and help give support to students. It’s helpful when I hang up an anchor chart for students to reference as well.

Then I’ll give them a Subtraction Doubles and Near Doubles worksheet as independent practice so I can really see where students are at with this mental strategy. Find the task cards, anchor chart, and worksheets I use with my students here.

I’ll continue to give students opportunities to use this mental strategy during our Math Fact of the Day warm up time, like mentioned above. Find my Math Fact of the Day resource here.

 

Use Addition to Subtract

It is easier for students to master addition facts than subtraction facts. But what if they could use their addition facts to help with subtraction?

When students figure out that they can use addition to solve subtraction facts quickly it is a game changer.

I help students do this with fact families. Fact families show how addition and subtraction are related. For example, if a student knows that 2 and 9 make 11. Then they can know that 11 take away 2 is 9.

I like to help my students master fact families with my fact family triangles resource. I laminate them so students can write on them with dry erase markers and I set them around the room. Then students work with a partner writing the 2 addition equations and the 2 subtraction equations that go with the related numbers.

This helps students see that if they memorize one addition equation they automatically know two subtraction equations, making this one of the most powerful mental math strategies for subtraction.

Find the fact family triangles I use in my classroom here. To learn more about teaching fact families to your students, read this blog post: 3 Reasons Why You Need to Teach Fact Families

 

Mental Math Strategies For Subtraction Grade 2

 

Now math facts are not the only subtraction that students do. For 2nd graders, they learn 2-digit subtraction and 3-digit subtraction. Students can use subtraction mental math strategies for these as well.

 

Break Apart Subtraction

For 2-digit subtraction I love break apart as a mental strategy. To help students understand this visually, I have them write out the equation and then draw a tens box and a ones box for the number they are subtracting. Then they can easily subtract the tens. 

For the ones, if they need to regroup they will need to break apart the ones again. You want them to break about the ones so that they can get down to the next tens number. Then they can subtract the other part to get their answer.

To better explain this, let’s look at an example. For the equation 85-28 you break the 28 apart into tens and ones. Then you subtraction your tens. 80-20 is 40. So you for a 4 for your tens number. Next you break apart your ones into 5 and 3. 5-5=0. So you put a 0 for your ones number. Now you are at 50. Then you subtract 3 more to get your answer which is 27. 

Find my 2-digit break apart practice activities here. 

For more teaching tips for 2-digit subtraction strategies, read this blog post here: How to Teach Those Tricky 2-Digit Subtraction Strategies

 

For 3-digit subtraction I have students write out their equation like 436-217=. We look at the hundreds. 4-2=2. We look at the tens 3-1=2. Then we look at the ones, but if we have 6 ones we can’t take away 7. So we need to break apart 7 into easier numbers. We need to break it apart into 6 and 1. That way we can do 6-6=0. So the number is 220 and then we just need to take away 1 more, so the answer is 219.

For this 3-digit strategy, students need instruction and practice. But soon it turns out to by my students’ favorite 3-digit subtraction strategy that I teach them. Breaking apart the number to make easier equations just makes sense to them. Learn more about how to teach this strategy plus the other 3-digit subtraction strategies I teach my 2nd graders here in this blog post: Subtraction Strategies For 3-Digit Numbers: How 2nd Grade Students Best Understand Them

Want to teach this strategy to your students but not sure where to start? I have a resource that makes it very straight forward to teach. There are display pages that help you with direct instruction. It includes scaffolded worksheets that help students think through all the steps. There are other fun practice activities like scoot activities and math puzzles that help students get the extra practice they need. Soon they are able to subtract 3-digit numbers completely in their heads! Find this resource here. You can also find it in a money-saving bundle with my other 3-digit subtraction strategy resources here.

 

Mental math strategies for subtraction help students get to the answer quickly and accurately. When you teach them explicitly to your students, let them get lots of practice, and then review them often, students can find success with them. Students will build their number sense and also their confidence in their mathematical abilities.

 

Getting students to math fact mastery can be hard work. I’m sharing what has helped my students best to reach math fact fluency here in this free workbook for 1st and 2nd grade teachers: The 7 Steps to Ensure Math Fact Fluency

Download your free copy here.