What is subtraction in simple words?

Subtraction is a way to find how many are left or how far apart two numbers are by taking one number away from another. It can mean taking away objects, breaking a total into parts, or counting back.

What is subtraction used for in real life?

Subtraction is used to track what is left after spending money, using ingredients, or giving away items. It is also used to compare amounts, such as finding how many more points one team has than another.

How do you explain what is subtraction to a child?

Start with objects they can move, like blocks or snacks. Show a starting amount, take some away, and count what is left, saying the subtraction sentence out loud, such as "7 − 3 = 4". Connect it to addition by showing that 4 + 3 = 7.

Why is subtraction the opposite of addition?

Addition puts amounts together to make a larger total, while subtraction starts with a total and takes a part away. Because they undo each other, knowing an addition fact helps your child solve the related subtraction fact, such as using 6 + 4 = 10 to solve 10 − 6 = 4.

What Is Subtraction? Definition and Examples

How to explain subtraction to a child

Subtraction is when you start with some things and take some away. The number gets smaller. For example, if you have 5 crackers and eat 2, you have 3 left. Subtraction helps answer questions like "How many are left?" or "How many more?"

Worked examples of subtraction

Example 1 (younger grades): simple take-away within 20

Problem: 14 − 6 = ?

Think of 14 as 10 and 4. First, subtract 4 from 6 to get to 10: 14 − 4 = 10. There are 2 more to subtract, so 10 − 2 = 8. So 14 − 6 = 8.

Example 2 (upper grades): subtracting with decimals and integers

Problem: 23.75 − 18.9 = ?

First, write 18.9 as 18.90 so both numbers have hundredths. Subtract the hundredths: 5 hundredths − 0 hundredths = 5 hundredths, so the hundredths digit is 5. Subtract the tenths: 7 tenths − 9 tenths cannot be done without regrouping, so regroup 1 one from 23 ones as 10 tenths. Now there are 22 ones and 17 tenths. Subtract tenths: 17 tenths − 9 tenths = 8 tenths. Subtract ones: 22 ones − 8 ones = 14 ones. Subtract tens: 2 tens − 1 ten = 1 ten. So 23.75 − 18.9 = 14.85.

Problem with integers: −3 − 5 = ?

Use the idea that subtracting a number is the same as adding its opposite, called the additive inverse. The additive inverse of 5 is −5, so −3 − 5 = −3 + (−5). Adding −3 and −5 gives −8. So −3 − 5 = −8.

Going deeper with subtraction

In early grades, subtraction is modeled as taking away objects, taking apart a total into parts, or counting back on a number line. Children learn that subtraction is related to addition, because if 8 − 3 = 5, then 5 + 3 = 8 is also true. These related facts are often called a fact family.

As your child moves into larger numbers, subtraction is explained using place value. For example, when subtracting within 1,000 or 1,000,000, regrouping means trading 1 hundred for 10 tens, or 1 ten for 10 ones, without changing the total amount. Students learn to choose efficient strategies, such as using mental math for easy facts within 20 or using the standard algorithm for larger multi-digit numbers.

In later grades, subtraction is extended to fractions, decimals, integers, and rational numbers. Students learn that subtracting any rational number is the same as adding its additive inverse, so p − q = p + (−q). This idea helps make sense of expressions like 3/4 − 1/2 or (−2.5) − (−1.1), and supports work with algebraic expressions and rational expressions.

Common mistakes with subtraction

Mixing up the order of the numbers. A child might think 5 − 12 is the same as 12 − 5 and answer 7. Subtraction is not commutative, so reversing the numbers changes the meaning and usually changes the answer.
Regrouping without thinking about place value. For 402 − 185, a child might try 2 − 5 and get stuck, or write 2 − 5 = 3 and get 323. The correction is to decompose 1 hundred into 10 tens, then decompose 1 ten into 10 ones, keeping track that 402 = 3 hundreds + 9 tens + 12 ones before subtracting.
Ignoring the signs with integers. For −3 − 5, a child might add the numbers and write 2, treating it like 5 − 3. The correction is to use the rule that subtracting 5 is the same as adding −5, so −3 − 5 = −3 + (−5) = −8.

Where subtraction shows up in everyday life

Subtraction appears any time something is used up, lost, or compared. When a child spends part of their allowance, counts how many game points they need to catch up, or notices how many more pages are left in a book, they are using subtraction to find what is left or how far apart two amounts are.

Related terms to explore

Subtraction is closely connected to addition and to the way number sentences are written. It also fits into families of related facts. You might also want to read about:

What is subtraction?