Subtraction Within 20 Worksheet

Every problem on this sheet starts from a number between 11 and 20, so most of them cross back over ten. The sheet has 30 problems for grades 1 and 2 and takes about 10 minutes.

Grade: Grade 1–2
Problems: 30
Time: About 10 minutes
Standard: 1.OA.C.6, 2.OA.B.2

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Two pages: the worksheet, then the answer key. No sign-up needed.

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Part A Subtract.

15 − 5 = 10
11 − 3 = 8
11 − 2 = 9
12 − 10 = 2
12 − 7 = 5
14 − 10 = 4
19 − 10 = 9
12 − 6 = 6
13 − 8 = 5
11 − 4 = 7
17 − 10 = 7
16 − 9 = 7
17 − 9 = 8
18 − 9 = 9
12 − 9 = 3

Part B Subtract. Check each answer by adding.

14 − 7 = 7
20 − 10 = 10
12 − 2 = 10
15 − 7 = 8
18 − 8 = 10
17 − 8 = 9
11 − 5 = 6
14 − 5 = 9
14 − 8 = 6
13 − 6 = 7
13 − 7 = 6
12 − 3 = 9
12 − 5 = 7
17 − 7 = 10
11 − 6 = 5

Tips for teachers and parents

Teach "back to ten." For 14 − 6, take 4 to get to 10, then 2 more to get to 8.
Or think addition: 15 − 8 asks "8 plus what makes 15?" The answer is 7.
Use the addition within 20 sheet alongside this one. Every fact here is a fact from that sheet run backwards.
Time Part A and Part B and record both scores. Faster recall means the facts are moving from counting to memory.

Common mistakes

Subtracting the ones digits the wrong way round, so 13 − 5 becomes 12 (from 5 − 3 = 2). Use a number line until "back to ten" is secure.
Answers off by one from counting back. Practice back to ten with a ten frame.

What to practice next

When the facts are quick, move on to 2-digit subtraction without regrouping.

Frequently asked questions

What is the back-to-ten strategy?

Subtract in two jumps: first down to 10, then the rest. 13 − 5 is 13 − 3 = 10, then 10 − 2 = 8.

When should children know subtraction facts to 20?

Second graders are expected to know them from memory by the end of the year.

How big are the answers?

Every answer is 10 or less, and the number taken away is between 1 and 10. That keeps the focus on the basic facts that cross ten.