Adding Tenths, Hundredths, and Thousandths
The most common decimal error is misalignment. These worksheets build the habit of "line up the dots" — the essential skill for all decimal operations.
Most parents worry about whether their child can compute the sum correctly. But the real question is whether they can set up the problem correctly. A child who adds 4.5 + 1.23 and writes 4.5 + 1.23 with the numbers right-aligned (instead of decimal-aligned) will get 4.5 + 1.23 = 5.73 — which happens to be correct in this example, hiding the error. But when they try 12.3 + 4.56, the same alignment mistake gives 12.3 + 4.56 = 16.86 instead of the correct 16.86 — wait, that is also correct? The problem is inconsistent. The fix is teaching the rule, not relying on coincidentally correct answers.
These worksheets are designed to make alignment visible and habitual. For students who need to build whole number addition fluency before decimals, see our addition basic facts worksheets and two-digit addition worksheets.
Three stages — do not rush to mixed place values
Start with problems where both numbers have the same number of decimal places (1.2 + 3.4 or 2.34 + 5.67). The child focuses only on alignment and addition without the complexity of place value differences. Spend 3-5 days on this stage.
Introduce problems where numbers have different lengths (4.5 + 1.23). Teach the "zero padding" strategy: write 4.5 as 4.50 so both numbers have hundredths. This stage builds the habit of aligning decimal points. Spend 5-7 days on this stage.
Combine different place values with carrying across place values (4.95 + 3.85). This is the hardest decimal addition skill. The child must align, pad with zeros, add each column, and carry when needed. Spend 5-7 days on this stage before moving to word problems.
Teach this script — say "line up the dots" every time
Write the numbers in a column with decimal points stacked vertically. Say: "Line up the dots." If numbers have different lengths, add zeros as placeholders (4.5 becomes 4.50).
Add the hundredths column (if any), then tenths, then ones, then tens — just like whole numbers. Carry when a column sums to 10 or more.
Write the decimal point in the answer directly below the stacked decimal points. Say: "The decimal point goes straight down." Check that the answer makes sense.
If your child continues to misalign decimal points despite practice, the issue is usually a habit from whole number addition. Our Math Foundations course (grades 4-6) includes explicit instruction in decimal alignment and place value understanding. You can also browse all available courses and planners on the resources page.
View Math Foundations — $57The next step after addition — same alignment rules
Build the foundation before operations
Apply addition to money and measurement
Build whole number fluency first
Full 4th grade math overview
Where decimal addition is mastered
Real questions parents ask about decimal addition
Our worksheets cover adding tenths to tenths (1.2 + 3.4), hundredths to hundredths (2.34 + 5.67), and mixed place value problems where numbers have different lengths (4.5 + 1.23). This last skill is often the most challenging because students must pad with zeros to maintain alignment.
This is usually a habit from whole numbers where right-alignment works. The fix is explicit practice with grid paper or worksheets that have pre-drawn decimal point columns. Have your child say "line up the dots" before every problem. Within 2-3 weeks, the correct alignment becomes automatic.
Start with same-place-value problems (tenths with tenths) until accuracy is high. Then introduce problems where one number has more digits after the decimal (4.5 + 1.23). Teach the "zero padding" strategy: 4.5 becomes 4.50 so both numbers have hundredths. Most children are ready for mixed place values after 1-2 weeks of same-place practice.
Careless errors in decimal addition are almost never careless — they usually signal weak whole-number regrouping skills. Go back to multi-digit whole number addition (like 45 + 78) until that feels automatic. The procedure is identical; if a child struggles with carrying in decimals, they will also struggle with carrying in whole numbers.
15-20 problems per session is the effective range. Practice should be short and daily — 10 minutes every day beats one long session per week. Stop when attention drops, because fatigued practice reinforces errors rather than correct alignment habits.
Yes — money is the most effective real-world context for decimals because dollars and cents are familiar. $3.50 + $1.25 is more intuitive than 3.50 + 1.25. Once the concept is solid, transition to abstract problems. Money examples are especially useful for children who struggle with the meaning of decimals.
First: same number of decimal places (1.2 + 3.4). Second: different decimal places with zeros in the shorter number (2.5 + 1.75 becomes 2.50 + 1.75). Third: different decimal places requiring regrouping across place values (4.95 + 3.85). Fourth: adding three or more decimal numbers. Each stage typically takes 3-5 days of focused practice.
Answer keys provide only the final correctly formatted decimal answer. This allows students to work through alignment independently while giving parents quick verification. If your child makes alignment errors, have them circle the decimal points before adding.
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