Adding & Subtracting Decimals
Practise adding and subtracting decimals — the one rule that matters is lining up the decimal points.
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How to add and subtract decimals
Adding and subtracting decimals is just like whole-number column work, with one extra rule on top: line up the decimal points. Once the points (and therefore the place values) are aligned, you add or subtract exactly as usual and bring the point straight down.
- Write the numbers so their decimal points line up vertically.
- Fill any gaps with zeros so both numbers have the same length.
- Add or subtract column by column, carrying or borrowing as normal.
- Bring the decimal point straight down into the answer.
Worked examples
Tips & common mistakes
The single most important habit is lining up the decimal points — not the last digits. Writing 3.4 + 2.75 means padding 3.4 to 3.40 first. Type your answer with the decimal-point key.
- Lining up the last digits instead of the decimal points (so 3.4 + 2.75 goes wrong).
- Forgetting to bring the decimal point down into the answer.
- Not padding with zeros, which makes the columns misalign.
Frequently asked questions
How do you add decimals?
Line up the decimal points, pad with zeros so both numbers are the same length, then add column by column and bring the point straight down.
Why line up the decimal points?
Because that lines up the place values — tenths under tenths, ones under ones — which is what makes column addition work.
How do you subtract decimals?
The same way: align the points, pad with zeros, then subtract with borrowing as usual.
How do I type my answer?
Use the number keys and the decimal-point key, e.g. 6 . 1.
What grade is this?
Adding and subtracting decimals is a grade 5 skill, building on whole-number column work.
Keep practising
← All decimalsRounding decimalsMultiplying decimals5th grade math