Adding and subtracting decimals

To add or subtract decimals, line up the decimal points, fill any gaps with zeros, then add or subtract like whole numbers and bring the point straight down. 3.5 + 1.25: write 3.50 + 1.25 = 4.75. This page explains why, has a tool for any two decimals, covers subtracting from whole numbers, and the common mistakes.

The big idea: line up the places

Just like whole numbers, you can only add ones to ones, tenths to tenths and hundredths to hundredths. Lining up the decimal points lines up all the places. Zeros added at the end (3.5 = 3.50) don’t change the value but fill the gaps so nothing gets lost.

How to add and subtract decimals, step by step

  1. Line up the decimal points, one under the other.
  2. Fill empty places with zeros so both numbers have the same number of decimal places.
  3. Add or subtract from right to left, carrying or borrowing as with whole numbers.
  4. Bring the decimal point straight down into the answer.
  5. Estimate to check: 3.5 + 1.25 is about 4 + 1 = 5.

Add or subtract any two decimals

The tool lines up the points and fills the gaps for you.

Worked examples

2.36 + 4.5

2.36 + 4.50 = 6.86.

8.4 − 3.75

8.40 − 3.75: borrow in the hundredths and tenths: 4.65.

5 − 1.38

Write 5 as 5.00: 5.00 − 1.38 = 3.62.

$12.99 + $7.45

Money always has two places: $20.44.

Common mistakes

3.5 + 1.25 = 1.60Lined up the right-hand digits.Fix: line up the decimal points: 3.50 + 1.25 = 4.75.
5 − 1.38 = 4.38Didn’t write 5 as 5.00.Fix: a whole number has a point at the end: 5.00.
8.4 − 3.75 = 5.35Took the smaller digit from the bigger in the hundredths.Fix: fill with zeros (8.40) and borrow.
Point in the wrong placePoint not brought straight down.Fix: keep the points in one column all the way.

How to teach it at home

Shopping totals

Add two prices and work out the change from $20.

Race times

How much faster was 12.85 seconds than 13.2 seconds? (0.35 s)

Measure and add

Add lengths in meters: 1.5 m + 0.75 m.

By grade

Worksheets and practice

Adding and subtracting decimals worksheet, page 1

Adding and subtracting decimals worksheet: printable PDF with an answer key. · Make a fresh test

All decimals · Decimals chart

Last reviewed

Questions parents ask

How do you add decimals?

Line up the decimal points, fill gaps with zeros, add as whole numbers and bring the point straight down.

How do you subtract a decimal from a whole number?

Write the whole number with a decimal point and zeros: 5 = 5.00. Then subtract: 5.00 − 1.38 = 3.62.

Why do you line up the decimal points?

So that tenths line up with tenths and hundredths with hundredths. It is the same as lining up ones and tens.

Do zeros at the end change a decimal?

No. 3.5, 3.50 and 3.500 are equal. Adding them just fills the gaps.

What grade learns adding decimals?

Grade 5 to hundredths (5.NBT.B.7); grade 6 fluently (6.NS.B.3).