Adding fluently within 20
In 2nd grade, children learn to add within 20 using mental strategies, and to know every sum of two one-digit numbers, like 8 + 7, from memory by the end of the year.
By Robert “Bobby” BarnettMath teacher, parent, and founder of Bobby’s Math Club
Try these with your child
These are real questions from our 2nd grade practice. Tap the speaker to hear one read aloud, or the light bulb for a hint, and talk about the answer together.
Question 1 of 3
What is 9 + 6?
- 14
- 15
- 16
Why this matters
Knowing addition facts by heart gives your child room to think about the interesting part of a problem. Sums like 8 + 7 sit inside bigger problems, such as 48 + 37 this year, and inside multiplying in 3rd grade. If the fact comes to mind without counting, your child's attention is free for the harder step. It shows up at home too: adding two dice, totaling a few scores, or counting snacks for friends.
Once these sums come quickly, subtracting fluently within 20 follows, and every fact your child knows here will help.
Where kids can get stuck
- Counting on fingers or by ones for facts like 8 + 6, which slows every larger problem and invites slips.
- Confusing near neighbors, such as answering 7 + 8 = 16 because the double 8 + 8 = 16 feels close.
- Treating 4 + 9 and 9 + 4 as two separate facts to learn, not seeing that swapping them keeps the sum at 13.
How you can help
- Roll two dice before dinner and take turns saying the total. Once those sums come easily, roll one die and add it to 8, then to 9, to practice the facts that cross ten.
- Pick a fact of the day, like 7 + 8, and bring it up at odd moments: at breakfast, in the car, and at bedtime. Let your child ask you one too.
- Write the facts your child still works out on scraps of paper and keep them in your pocket. Pull one out while you wait in line, and retire it once it comes quickly three days running.
Want a little more? Watch the kid-friendly video below together, or try Bobby's Math Club for free practice that adapts to your child.
Kid-friendly explanation
Questions parents ask
Why is my child learning facts through strategies if the goal is memory?
Strategies help your child see how facts connect, such as using 7 + 7 to find 7 + 8. Facts learned this way are easier to remember and can be rebuilt if one slips away. Memory still matters. By the end of 2nd grade, your child is expected to know every sum of two one-digit numbers from memory, and strategies are the road there.
How fast should my child know their addition facts?
The goal is that facts come quickly and comfortably, without counting, so they don't slow down bigger problems. There is no single required speed. If your child answers most facts within a few seconds and uses a quick strategy for the rest, they are on track. Pressure can make facts harder to recall, so keep practice light and short.
Which addition facts are usually hardest to memorize?
Facts like 7 + 8, 6 + 8, 8 + 5, and 9 + 7 tend to take longest. Facts with 0, 1, and 2, the doubles, and the pairs that make 10 usually come first. Focusing on the handful your child is still unsure of works better than reviewing the whole set every time. And each fact they learn also covers its turnaround, so 8 + 5 brings 5 + 8 with it.
Make learning math fun
Bobby's Math Club turns 2nd grade math practice into something fun to do together.
- Unlimited free practice
- A few minutes a day, at just the right level
- Level-ups, badges, and a cheer for every win
Written by Robert “Bobby” Barnett
Bobby is an award-winning math teacher, the author of Meet Every Learner’s Needs, and the father of two elementary-school math learners. He uses Bobby’s Math Club with his own kids a few times every week. Learn more or contact Bobby.
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Join the clubNote for teachers: This skill is covered by Common Core math standard 2.OA.B.2: “Fluently add and subtract within 20 using mental strategies. By end of Grade 2, know from memory all sums of two one-digit numbers.” Learn how Bobby's Math Club can help your students grow. (Common Core 2.OA.2)