Singapore Math adding and subtracting fractions guide for families and teachers outside Singapore. What students learn from Primary 2 to Primary 5, how Singapore builds the skill in stages, and how to practise it at home.
Fractions can only be added when they count the same size of part.
Every method in this topic is a way of making that true.
In Singapore Mathematics, adding and subtracting fractions develops across four years of the current primary syllabus. Primary 2 starts with like fractions, Primary 3 adds related fractions, Primary 4 allows two different denominators, and Primary 5 adds and subtracts mixed numbers.
After that, fractions are multiplied in Primary 5 and divided in Primary 6.
This guide is useful for families and teachers who want to:
- see exactly what Singapore expects at each level;
- teach the steps in the order Singapore uses;
- prepare a child who is moving into a Singapore school; or
- support a student using Singapore Math materials in another country.
Quick facts
Level: Primary 2 to Primary 5 (Standard Mathematics)
Strand: Number and Algebra
Official source: MOE Primary Mathematics Syllabus, the 2021 syllabus first examined at PSLE in 2026
Comes after: Equivalent Fractions and Factors and Multiples
Leads to: Mixed Numbers and Improper Fractions and Multiplying Fractions
What Adding and Subtracting Fractions Means in Singapore Mathematics
2 sevenths plus 3 sevenths is 5 sevenths. The parts are the same size, so we simply count them.
1/2 + 1/3 is different. Halves and thirds are different sizes, so they cannot be counted together yet.
The fix is to rename both fractions so they count the same size of part. 1/2 = 3/6 and 1/3 = 2/6, so 1/2 + 1/3 = 5/6.
The new denominator is a common multiple of the old ones. The smallest such number, the lowest common multiple, keeps the numbers small.
Mixed numbers, such as 3 1/4 (three and one quarter), add one more step: the whole numbers and the fractions both need attention.
Where Adding and Subtracting Fractions Sits in the Singapore Syllabus
In the current primary syllabus, the skill builds in clear stages.
| Level | What students add and subtract |
|---|---|
| Primary 2 | Like fractions within one whole, denominators not exceeding 12 |
| Primary 3 | Two related fractions within one whole, denominators not exceeding 12 |
| Primary 4 | Fractions with denominators not exceeding 12 and no more than two different denominators |
| Primary 5 | Mixed numbers |
Some details sit around these limits:
- Primary 3 also covers equivalent fractions and the simplest form, which the later stages depend on.
- Mixed numbers and improper fractions are introduced in Primary 4, before they are added and subtracted in Primary 5.
- Primary 5 Foundation Mathematics covers adding and subtracting with denominators not exceeding 12 and no more than two different denominators, and mixed numbers, without calculator.
- Fractions are not multiplied until Primary 5, and not divided until Primary 6.
How Singapore Teaches Adding and Subtracting Fractions
1. Count like fractions
2/7 + 3/7 = 5/7. Say it in words: “2 sevenths and 3 sevenths make 5 sevenths.”
2. Rename one fraction
For related fractions such as 1/2 + 3/8, only one fraction needs renaming: 1/2 = 4/8.
3. Rename both fractions
For 2/3 + 1/4, find a common multiple of 3 and 4. Using 12: 8/12 + 3/12 = 11/12.
4. Simplify the answer
Write the answer in simplest form, and as a mixed number if it is more than 1.
5. Handle mixed numbers
Add or subtract the whole numbers and the fractions, renaming 1 whole as a fraction when needed.
6. Check with the opposite operation
After subtracting, add the answer back. After adding, subtract one part.
A drawn bar or strip makes each stage visible. It is worth drawing until the child can explain why the denominators must match.
Worked Examples
Two different denominators (Primary 4)
Question: Find 5/6 − 1/4.
Step 1. The denominators are 6 and 4. Their lowest common multiple is 12.
Step 2. Rename: 5/6 = 10/12 and 1/4 = 3/12.
Step 3. 10/12 − 3/12 = 7/12.
Step 4. 7 and 12 share no common factor, so 7/12 is in simplest form.
Check: 7/12 + 3/12 = 10/12 = 5/6.
Subtracting mixed numbers (Primary 5)
Question: Find 3 1/4 − 1 2/3.
Step 1. Rename the fractions with denominator 12: 3 1/4 = 3 3/12 and 1 2/3 = 1 8/12.
Step 2. 3/12 is less than 8/12, so rename one whole: 3 3/12 = 2 15/12.
Step 3. Subtract the whole numbers: 2 − 1 = 1.
Step 4. Subtract the fractions: 15/12 − 8/12 = 7/12. The answer is 1 7/12.
Check: 1 7/12 + 1 8/12 = 2 15/12 = 3 3/12 = 3 1/4.
Another route is to change both mixed numbers to improper fractions: 13/4 − 5/3 = 39/12 − 20/12 = 19/12 = 1 7/12. Both methods give the same answer.
Common Mistakes
- Adding the denominators. 1/2 + 1/3 is written as 2/5. Fix: ask “are these the same size of part?” A drawing shows that 2/5 is less than 1/2, which cannot be right.
- Renaming only the denominator. 2/3 becomes 2/12. Fix: multiply the numerator by the same number: 2/3 = 8/12.
- Subtracting the smaller fraction from the larger. In 3 1/4 − 1 2/3, a child works out 2/3 − 1/4 instead. Fix: when the first fraction is smaller, rename one whole first.
- Forgetting the whole numbers. A child subtracts the fractions correctly and drops the 2 − 1. Fix: write the whole-number step on its own line.
- Leaving an answer unsimplified. 3/6 is left as it is. Fix: always check for a common factor at the end: 3/6 = 1/2.
Teaching Adding and Subtracting Fractions Outside Singapore
The mathematics is the same everywhere, but Singapore spreads it carefully over four years.
- Pace. Singapore keeps each stage within limits: like fractions first, then related fractions, then two different denominators up to 12. Your local curriculum may move faster or slower, so decide by readiness. The Singapore Math Placement guide can help.
- Terms. Singapore says “like”, “unlike” and “related” fractions. Others say “same denominator” or “different denominators”.
- LCM. Singapore says “lowest common multiple”. Some materials say “least common multiple”. Both shorten to LCM, and any common multiple works; the lowest just keeps numbers small.
- Prerequisites. Equivalent fractions and multiplication tables must be secure first.
- Calculators. PSLE Paper 1 does not allow calculators, so written fraction methods matter.
How to Practise Adding and Subtracting Fractions at Home
A short, mixed routine works well.
- Add two like fractions aloud in words, then in symbols.
- Rename two fractions to a common denominator without adding them.
- Add one pair and subtract one pair with different denominators.
- At Primary 5 level, do one mixed-number subtraction that needs renaming.
- Check every answer with the opposite operation.
- Once a week, solve one word problem, such as fractions of a ribbon used and left.
Ten to fifteen minutes is enough when each step is written clearly.
Try These
- Find 2/9 + 5/9.
- Find 1/2 − 1/6. Give your answer in simplest form.
- Find 2/3 + 1/4.
- Find 4 1/5 − 2 1/2.
Answers
- 7/9. These are like fractions, so count the ninths: 2 + 5 = 7.
- 1/3. 1/2 = 3/6, so 3/6 − 1/6 = 2/6 = 1/3.
- 11/12. 2/3 = 8/12 and 1/4 = 3/12, so 8/12 + 3/12 = 11/12.
- 1 7/10. 4 1/5 = 4 2/10 = 3 12/10 and 2 1/2 = 2 5/10. Then 3 − 2 = 1 and 12/10 − 5/10 = 7/10.
What Comes Next
Adding and subtracting fractions supports almost all later fraction work.
- Mixed Numbers and Improper Fractions explains renaming between the two forms in detail.
- In Primary 5, Multiplying Fractions begins.
- In Secondary 2, Algebraic Fractions uses the same common-denominator idea with letters.
A child who understands why denominators must match will recognise the same step in algebra.
Frequently Asked Questions
When do Singapore students learn to add and subtract fractions?
It starts in Primary 2 with like fractions and builds each year. Primary 5 adds and subtracts mixed numbers.
Do Primary 4 students add fractions such as 1/3 + 1/4 + 1/6?
The Primary 4 limit is no more than two different denominators, each not exceeding 12. Three different denominators go beyond that limit.
Must my child use the lowest common multiple?
No. Any common multiple gives the right answer. The lowest common multiple keeps the numbers smaller and simplifying easier.
Should mixed numbers be changed to improper fractions first?
Either method is correct. Working with whole numbers and fractions separately often keeps the numbers smaller.
Are answers greater than 1 allowed?
At Primary 2 and 3, adding and subtracting stays within one whole. From Primary 4, students work with mixed numbers and improper fractions.
Why is subtraction harder than addition?
Subtracting mixed numbers often needs renaming one whole. Practise that step on its own first.
Helpful Reading
- Singapore Mathematics | International Edition: Equivalent Fractions
- Singapore Mathematics | International Edition: Mixed Numbers and Improper Fractions
- Singapore Mathematics | International Edition: Factors and Multiples
- Primary Mathematics: Fractions of a Quantity, Equivalence and Operations
- Why Do Fractions Keep Causing Problems in Later Mathematics?
- Singapore Math Bar Model | A Guide to Model Drawing
- How to Make Sense of the PSLE Mathematics Syllabus in Singapore
- MOE Primary Mathematics Syllabus
Adding and Subtracting Fractions in Singapore Mathematics
Same size of part first.
Rename, then count.
Watch the whole numbers.
Simplify at the end.
Check with the opposite operation.
Taught in stages, this topic stops being a list of rules.
It becomes one idea used carefully at each level.
Ask Bukit Timah Tutor
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If your child is learning Singapore Mathematics at home, in an international school or in a Singapore school, and you are unsure where to begin with this topic, send us a short message with the student’s level and one example of the work.
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Singapore Mathematics | International Edition is a Bukit Timah Tutor guide series for families and teachers outside Singapore. It is not a textbook and is not affiliated with MOE, SEAB or any publisher. Syllabus details were checked against MOE and SEAB documents in October 2026. Always confirm current requirements with your school.
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