How to Subtract 3-Digit Numbers: A Step-by-Step Guide

Learning how to subtract 3-digit numbers is an important math skill for 3rd graders. Students build on what they already know about place value and subtraction as they learn to subtract hundreds, tens, and ones. While some problems are straightforward, others require regrouping, which can make subtraction a little more challenging.

The good news? With a little practice and a clear set of steps, students can become more confident subtracting 3-digit numbers!

In this post, we'll walk through how to subtract 3-digit numbers with and without regrouping, along with a few tips to help students master this important skill.

What Does It Mean to Subtract 3-Digit Numbers?

A 3-digit number has three place values: hundreds, tens, and ones.

For example, in the number 456:

• 4 represents 4 hundreds, or 400.

• 5 represents 5 tens, or 50.

• 6 represents 6 ones, or 6.

When subtracting 3-digit numbers, students need to line up the hundreds, tens, and ones correctly. Keeping the digits in the correct columns helps students subtract accurately.

How to Subtract 3-Digit Numbers Without Regrouping

Let's start with a problem that doesn't require regrouping.

Example: 586 − 243 = ?

Follow these steps:

1. Subtract the ones. Subtract 3 from 6 to get 3.

2. Subtract the tens. Subtract 4 from 8 to get 4.

3. Subtract the hundreds. Subtract 2 from 5 to get 3.

The answer is 343!

When the top digit in each column is greater than or equal to the bottom digit, students can subtract without regrouping.

How to Subtract 3-Digit Numbers With Regrouping

Sometimes, the top digit is smaller than the bottom digit in one of the columns. When this happens, students need to regroup.

Regrouping means exchanging value from one place-value column for an equivalent amount in the next column. For example, 1 ten can be exchanged for 10 ones.

Let's look at an example.

Example: 532 − 178 = ?

Step 1: Subtract the ones.

We cannot subtract 8 from 2, so we need to regroup. Take 1 ten from the 3 tens. That leaves 2 tens, and the 2 ones become 12 ones.

Now subtract: 12 − 8 = 4.

Step 2: Subtract the tens.

We now have 2 tens, but we cannot subtract 7 tens from 2 tens. We need to regroup again.

Take 1 hundred from the 5 hundreds. That leaves 4 hundreds, and the 2 tens become 12 tens.

Now subtract: 12 − 7 = 5.

Step 3: Subtract the hundreds.

We have 4 hundreds remaining. Subtract 1 hundred from 4 hundreds to get 3 hundreds.

The answer is 354!

Encourage students to work from right to left, starting with the ones. Remind them to keep track of any regrouping so they don't forget to adjust the digit in the next column.

Tips for Teaching 3-Digit Subtraction

If your students are struggling with subtraction, try these simple strategies to help make the process easier.

1. Review place value first.

Make sure students understand the value of each digit in a 3-digit number. Place-value charts and base-ten blocks can help students see how hundreds, tens, and ones are related.

2. Model each step.

Work through examples together before asking students to solve problems independently. Think aloud as you subtract and explain why regrouping is necessary.

3. Practice one skill at a time.

Begin with subtraction without regrouping. Once students feel comfortable, introduce regrouping in the ones column, followed by regrouping in the tens column. Then move on to problems that require regrouping in more than one column.

4. Encourage students to check their answers.

Students can check subtraction by adding the difference to the number they subtracted. For example, if 532 − 178 = 354, they can check their work with 354 + 178 = 532.

5. Provide plenty of practice.

Like any math skill, subtraction takes practice. A variety of problems can help students build accuracy, recognize patterns, and gain confidence.

Practice Subtracting 3-Digit Numbers

Ready to give your students some practice? Try these problems!

1. 764 − 321 = _____

2. 685 − 247 = _____

3. 923 − 456 = _____

4. 541 − 186 = _____

Answer Key: 1. 443, 2. 438, 3. 467, 4. 355

Have students explain how they solved each problem. Asking them to describe when and why they regrouped can help you see whether they understand the process.

Make 3-Digit Subtraction Easier With Hands-On Practice

Students often benefit from having the steps in front of them as they learn a new math skill. Visual examples, guided practice, and interactive activities can make subtraction less overwhelming and help students work more independently.

A subtraction flip book is one way to give students a reference they can use as they work through each step. Students can review the process, follow examples, and refer back to the instructions when they need a reminder.

If you're looking for a simple way to help your students practice subtracting 3-digit numbers, check out my 3-Digit Subtraction Flip Books at Math With Raven. These resources provide step-by-step support students can use as they learn and practice subtraction.

Raven's Thoughts

Learning how to subtract 3-digit numbers takes time, especially when regrouping is involved. By reviewing place value, modeling each step, and providing plenty of practice, you can help students develop the skills they need to solve subtraction problems with confidence.

Remember to start simple, build on what students already know, and celebrate their progress along the way!