How to Help Your First Grader Add Within 20

Quick answer

To help your first grader add within 20, teach them three mental math strategies: counting on from the bigger number, making ten, and using doubles. Start with problems where the answer is 10 or less, then move to teen sums. Practice a little every day with real objects, games, or short problem sets. Most kids master this by the end of 1st grade.

Adding within 20 is the foundation of all the math your child will do in elementary school. It’s where they stop counting one by one and start seeing patterns and shortcuts. Below is how to teach the strategies, what mistakes to watch for, and how to practice at home.

What is adding within 20?

Adding within 20 means solving addition problems where both addends (the numbers being added) and the sum (the answer) are 20 or less. Examples: 7 + 5, 9 + 8, 12 + 6.

This skill is a core part of 1st grade math and maps to Common Core standard 1.OA.C.6, which says children should “add and subtract within 20, demonstrating fluency for addition and subtraction within 10.” Fluency means your child can solve these problems quickly and accurately, without needing to count on their fingers every time.

Strategy 1: Counting on from the bigger number

Counting on is the simplest strategy and the one most kids learn first. Instead of counting from 1, your child starts at the bigger number and counts up by the smaller number.

Take 8 + 5:

Start at 8 (the bigger number).
Count up 5: “9, 10, 11, 12, 13.”
The answer is 13.

This works best when one number is small (1, 2, or 3) because there’s less counting to do. For 12 + 3, starting at 12 and counting “13, 14, 15” is much faster than counting from 1.

Strategy 2: Making ten

Making ten is the strategy that turns hard problems into easy ones. The idea is to break one number into parts so you can make 10 with the other number first, then add what’s left.

Take 8 + 5:

8 needs 2 more to make 10.
Break the 5 into 2 and 3.
Add 8 + 2 = 10, then add 10 + 3 = 13.

This strategy works especially well for problems where one number is 8 or 9, because you’re close to 10 already. For 9 + 6, you take 1 from the 6 to make 10, then add the leftover 5: 10 + 5 = 15.

Strategy 3: Using doubles and near doubles

Doubles are addition facts where both numbers are the same: 6 + 6, 7 + 7, 8 + 8. Most kids memorize these quickly because they have a rhythm. Once your child knows the doubles, they can use them to solve near doubles (problems where the numbers are one apart).

Take 7 + 8:

Your child knows 7 + 7 = 14.
Since 8 is one more than 7, the answer is one more than 14.
7 + 8 = 15.

This strategy is fast once the doubles are automatic. Spend a few minutes memorizing the doubles from 1 + 1 to 10 + 10, and near doubles become easy.

The 3 mistakes kids make most (and how to fix them)

Fun ways to practice adding within 20 at home

Practice sticks when it feels like play. A few ideas:

Dice games: roll two dice and race to add them. Use a timer and see how many they can solve in two minutes.
Card war: flip two cards each, add them up, and the higher sum wins the round.
Real-life math: “You have 8 grapes and I give you 5 more. How many now?” or “We need 12 crackers. You have 7. How many more?”
Flashcards with a twist: instead of drilling the same facts, let your child pick three cards and choose which one to solve first. Choice keeps them engaged.

Keep sessions to five or ten minutes. When your child gets one wrong, ask “What strategy could help here?” and let them try again before you give the answer.

How to know your child is ready to move on

Your child has mastered adding within 20 when they can:

Solve most addition problems within 20 in a few seconds, without counting on their fingers.
Choose and use a mental math strategy (counting on, making ten, or doubles) that fits the problem.
Explain why a strategy works (“I made ten first because 9 is close to 10”).
Add within 10 automatically, without hesitation.

When those feel solid, the natural next steps are subtraction within 20 and adding within 100, which build on these same strategies.

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The easiest way to give your child practice

For most parents, the hardest part of teaching adding within 20 isn’t the math. It’s finding enough of the right problems and keeping your child willing to do them. That’s where Octolearn helps: describe the skill (“adding within 20 using mental math strategies”), and it builds a grade-matched practice set with read-aloud support, a hint and a second try on every question, and stars and streaks that keep kids coming back. It’s free to try, and it turns five minutes of practice into something your child actually looks forward to.

Frequently asked questions

What does adding within 20 mean?

Adding within 20 means solving addition problems where both numbers and the answer are 20 or less, such as 8 + 5 or 12 + 7. This is a core 1st grade skill (Common Core standard 1.OA.C.6) where children move beyond counting by ones and learn mental math strategies like making ten or using doubles.

What grade do kids learn to add within 20?

Most children learn to add within 20 in 1st grade, building on the addition within 10 they learned in kindergarten. By the end of 1st grade, they should be able to add and subtract within 20 fluently, meaning quickly and accurately without counting on their fingers for every problem.

What are the best strategies for adding within 20?

The three most helpful strategies are counting on (start at the bigger number and count up), making ten (break one number into parts that make 10 with the other), and using doubles (know that 7 + 7 = 14, so 7 + 8 is one more). Each strategy fits different problems, and kids who know all three can pick the easiest one each time.

Should my child still be counting on their fingers in first grade?

Counting on fingers is a normal step, especially at the start of 1st grade. The goal is to gradually move toward mental strategies so your child doesn't need fingers for every problem by the end of the year. If they're still finger-counting every single problem in the second half of 1st grade, spend time on the strategies below to build fluency.

How can I practice adding within 20 at home without a fight?

Keep practice sessions short (five to ten minutes), use real-life situations like adding up snacks or toys, and make it a game with dice, cards, or a timer. Apps like Octolearn turn practice into a streak-and-reward system that keeps kids motivated, and the read-aloud feature means they can practice independently while you make dinner.