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Common Core Math1st GradeNumbers in Base Ten

1.NBT.4: Add Within 100

Also written as 1.NBT.C.4 and CCSS.MATH.CONTENT.1.NBT.C.4 · Cluster: Use place value understanding and properties of operations to add and subtract.

Make an Addition WorksheetAll 21 1st Grade Math Standards

The Official Wording

Add within 100, including adding a two-digit number and a one-digit number, and adding a two-digit number and a multiple of 10, using concrete models or drawings and strategies based on place value, properties of operations, and/or the relationship between addition and subtraction; relate the strategy to a written method and explain the reasoning used. Understand that in adding two-digit numbers, one adds tens and tens, ones and ones; and sometimes it is necessary to compose a ten.

Common Core State Standards, Grade 1, Number & Operations in Base Ten · Read it at the source · Checked October 14, 2026

What 1.NBT.4 Means in Plain English

First graders add a two-digit number and a one-digit number, like 36 + 7, or a two-digit number and a multiple of ten, like 36 + 20, with rods, cubes or quick drawings. Tens go with tens, ones with ones, and 13 loose ones become a new ten.

Each model gets tied to a written method and explained in words, so 36 + 7 might read 36 + 4 = 40, then 40 + 3 = 43. In 2nd grade students add two two-digit numbers like 47 + 38 fluently (2.NBT.5).

1.NBT.4 I Can Statements

  • I can add a one-digit number to a two-digit number.
  • I can add tens to a two-digit number.
  • I can make a new ten when there are too many ones.

1.NBT.4 Worked Example

Both kinds of sum the standard names, one that makes a new ten and one that adds whole tens, built before they are written.

Problem

Solve 28 + 6. Then solve 28 + 30.

A new ten, then whole tens
  1. Build 28 with rods and cubes: 2 tens and 8 ones. Add 6 more cubes.2 tens and 14 ones
  2. 14 ones is too many for the ones place. Snap ten of them into a new ten.14 ones = 1 ten and 4 ones
  3. Now count what is there: 3 tens and 4 ones.28 + 6 = 34
  4. For 28 + 30, add the 3 new tens to the 2 tens. The ones do not change.2 tens + 3 tens = 5 tens
  5. Explain it in numbers: tens with tens, then the ones.20 + 30 = 50, 50 + 8 = 58
Answer28 + 6 = 34 and 28 + 30 = 58

Check it: Count on for the first: 29, 30, 31, 32, 33, 34 is six counts. For the second, count on by tens from 28: 38, 48, 58.

Common Mistakes with 1.NBT.4

Adding tens as ones

28 + 30 written as 31, the 3 tens added to the ones

Try this: Build both numbers with rods and cubes first so students see 30 is three rods, then add rods to rods.

Leaving 14 in the ones place

28 + 6 = 214

Try this: Keep a rule at the table: no more than 9 cubes in the ones place, so 10 loose cubes get snapped into a rod.

Counting on by ones for everything

28 + 30 counted 29, 30, 31 ... all the way to 58 on fingers

Try this: Ask how many tens are being added before anyone counts, then count on by tens: 38, 48, 58.

Where 1.NBT.4 Fits

Comes Before1.NBT.2Know that a two-digit number is tens and ones.1.OA.6Add within 20 with strategies like making ten.
Alongside1.NBT.5Find 10 more or 10 less in your head.1.NBT.6Subtract multiples of 10 within 90.
Comes Next2.NBT.5Add and subtract within 100 fluently with place-value strategies.2.NBT.7Add and subtract within 1,000 with models and written methods.

Practice 1.NBT.4

Addition Worksheet GeneratorFree ToolTwo-digit plus one-digit sums like 47 + 6, with and without a new ten, plus two-digit plus tens like 47 + 30. Answer key included.Two-digitWithin 100Answer key
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Quick Check

  1. Solve 45 + 8.
  2. Solve 62 + 30.
  3. The class has 54 crayons and gets a new box of 9. How many crayons does the class have now?

1.NBT.4: Other Names

1.NBT.41.NBT.C.4CCSS.MATH.CONTENT.1.NBT.C.4

Common Core State Standards © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved. Official wording from the Common Core State Standards PDFs at corestandards.org, last checked October 14, 2026. The explanation, I can statements, example, mistakes and practice on this page are EMStudio’s own, written beside the official wording. They are not part of the standard.