Math
Adding Fractions Calculator
Add two, three, four, or five fractions, mixed numbers, whole numbers, or decimals in one go.
The calculator finds the least common denominator from prime factors, rewrites every fraction over it, adds the numerators, simplifies with the GCF, and shows the answer as a simplified fraction, mixed number, decimal, and percent, with a fraction-strip picture of the sum.
Type a fraction (3/4), a mixed number (2 1/3), a whole number, or a decimal (1.75). Repeating decimals work too: 0.(3).
Second fraction or mixed number.
Leave blank to add only two fractions.
Fourth fraction, if you have one.
Fifth fraction, if you have one.
Try an example
Result
Sum (simplified)
—
- Mixed number
- —
- Decimal
- —
- Percent
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- Least common denominator
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Student quick launch
Grade planning, algebra checks, and formulas students reach for most.
Study path
Use this calculator with
Follow these when you want the formula behind the answer, a short lesson, or nearby tools in the same topic.
How to add fractions
Fractions can only be added when they count the same size of piece, so the first job is to give every fraction the same The bottom number of a fraction; it says how many equal parts make one whole.. The The smallest bottom number two fractions can share so you can add or compare them. (LCD) is the smallest number every denominator divides into. Rewrite each fraction over the LCD, add the The top number of a fraction; it counts how many parts you have., keep the denominator, then simplify.
Adding mixed numbers
Convert each A whole number written next to a fraction, like 2 1/3. to an A fraction whose top number is at least as big as its bottom number, like 7/3. first: whole × denominator + numerator, over the same denominator. 2 1/3 becomes (2 × 3 + 1)/3 = 7/3. Add the improper fractions as usual, then convert the sum back to a mixed number if you want one. This avoids the classic mistake of adding the whole parts and fraction parts separately and forgetting to carry.
| Input style | Example | Read as |
|---|---|---|
| Fraction | 3/4 | 3 ÷ 4 |
| Mixed number | 2 1/3 | 2 + 1/3 = 7/3 |
| Negative mixed number | -2 1/3 | -(2 + 1/3) = -7/3 |
| Whole number | 5 | 5/1 |
| Decimal | 1.75 | 7/4 |
| Repeating decimal | 0.(3) or 0.333... | 1/3 |
Why the LCD instead of any common denominator?
Multiplying all the denominators together always gives a common denominator, but it is usually bigger than necessary and leaves a lot of simplifying at the end. For 1/4 + 1/6, the product 24 works, but the LCD 12 gives 3/12 + 2/12 = 5/12 with nothing left to simplify. The calculator shows the A whole number above 1 whose only factors are 1 and itself. factorization of every denominator so you can see why the LCD is what it is.
How to use it
- Type each fraction, mixed number, whole number, or decimal into its own box. Leave the optional boxes blank to add only two fractions.
- Use a space between the whole part and the fraction for mixed numbers (2 1/3) and put a minus sign in front for negative values (-2 1/3).
- Read the simplified sum in the dark panel, with the mixed number and decimal beside it.
- Open Show the work to see the prime factorization of each denominator, the LCD, each rewritten fraction, the numerator addition, and the simplification.
How to read the answer
The simplified fraction is the exact answer. The mixed number tells you how many wholes the sum contains, the decimal is handy for comparing sizes, and the percent is the same value out of 100. If the sum is negative, the larger negative fractions outweighed the positive ones.
Common mistakes and edge cases
- Never add the denominators. 1/4 + 1/4 is 2/4 = 1/2, not 2/8.
- Every denominator must be a nonzero whole number. A denominator of 0 is undefined and the calculator will refuse it.
- Mixed numbers need a space: 2 1/3. Writing 21/3 means twenty-one thirds.
- Adding only the fraction parts of mixed numbers and forgetting the wholes. 2 1/3 + 1 3/4 is 4 1/12, not 1 1/12.
- A mixed number's fraction part must be proper. 2 5/3 should be written as 11/3 or 3 2/3.
- The simplified answer, the unsimplified sum, and the decimal are all the same value written differently. Simplifying does not change the amount.
- Very large denominators can push the LCD past what exact arithmetic can handle; the calculator warns instead of rounding silently.
Worked examples
Three unlike denominators
1/4 + 1/6 + 2/9
Sum (simplified)
23/36
Two mixed numbers
2 1/3 + 1 3/4
Sum (simplified)
49/12
Negative fraction
-3/4 + 1/4
Sum (simplified)
-1/2
Sum is a whole number
1/3 + 2/3
Sum (simplified)
1
Decimal plus fraction
0.75 + 1/8
Sum (simplified)
7/8
Four fractions
1/2 + 1/3 + 1/4 + 1/5
Sum (simplified)
77/60
Repeating decimal
0.(3) + 1/6
Sum (simplified)
1/2
Same denominator
2/7 + 3/7: add the numerators, keep the denominator
Sum (simplified)
5/7
Whole number plus a fraction
3 + 2/5
Sum (simplified)
17/5
Five fractions (pizza leftovers)
5 × 4/6 + 4 × 3/8 + 3 × 6/12 + 1/2 + 1/3
Sum (simplified)
43/6
Subtracting by adding a negative
3/9 + (-2/8) = 1/12
Sum (simplified)
1/12
Zero denominator
1/2 + 1/0 is undefined
Sum (simplified)
Error
Frequently asked questions
How do you add fractions with different denominators?+
Find the least common denominator, rewrite each fraction with that denominator by multiplying its numerator and denominator by the same number, add the numerators, keep the denominator, and simplify. For 1/4 + 1/6 the LCD is 12: 3/12 + 2/12 = 5/12.
Can this calculator add mixed numbers?+
Yes. Type them with a space, like 2 1/3. Each mixed number is converted to an improper fraction before adding, and the answer is shown as a mixed number again.
How many fractions can I add at once?+
Up to five. Leave the optional boxes blank to add just two or three. The LCD is found for all of the denominators at once, so five fractions take exactly the same steps as two.
How do you add fractions with the same denominator?+
Add the numerators and keep the denominator: 2/7 + 3/7 = 5/7. The denominator says how big each piece is, and adding does not change the size of the pieces. Simplify at the end if the numerator and denominator share a factor.
How do you add a whole number to a fraction?+
Write the whole number over 1 (3 = 3/1), then use the fraction's denominator as the LCD: 3 + 2/5 = 15/5 + 2/5 = 17/5 = 3 2/5. Typing 3 in any box does this automatically.
Is cross-multiplying a valid way to add two fractions?+
Yes. a/b + c/d = (ad + bc)/(bd) always works, and the calculator shows it as a check whenever you add exactly two fractions. Its drawback is that bd is often larger than the LCD, so you usually have to simplify afterward.
What is the difference between the LCD and the LCM?+
They are the same number. The least common denominator of a set of fractions is the least common multiple of their denominators.
Why is my answer an improper fraction?+
When the sum is larger than one whole, the numerator is bigger than the denominator. That is still correct. The mixed-number form shows the same value as wholes plus a proper fraction.
Can I add negative fractions?+
Yes. Put the minus sign at the front: -3/4 or -2 1/3. Adding a negative fraction is the same as subtracting its positive version.
Does the calculator accept decimals?+
Yes. Decimals are converted to exact fractions first (1.75 becomes 7/4), and repeating decimals can be written as 0.(3) or 0.333... to get exactly 1/3.
About this calculator
- Written by
- mathcheck editorial team
- Last reviewed
- September 4, 2026
Method
- Uses the values entered by the user and stable formulas documented on the page.
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Last updated: September 4, 2026