Fraction Calculator
Use your own numbers after reviewing the formula and worked example.
Quick answer
Fractions need a common denominator before their numerators can be added or subtracted.
Formula or method
Keep units, percentages and time periods consistent. The formula is useful as a transparent check on the calculator result and helps explain why changing one input changes the answer.
Step-by-step
- Find a common denominator.
- Rewrite both fractions with that denominator.
- Add or subtract numerators.
- Reduce the final fraction.
Worked example
For 1/3 + 1/4, rewrite as 4/12 + 3/12 = 7/12.
How to interpret the result
Using the least common denominator can keep arithmetic smaller, but any valid common denominator works.
When the answer is used for a purchase, loan, payroll decision, construction order, school grade, health estimate or other real-world choice, verify the assumptions that matter in that context. Accurate arithmetic still depends on accurate inputs.
Common mistakes
- Adding denominators.
- Changing denominator without changing numerator proportionally.
- Forgetting to reduce.
Frequently asked questions
Can same-denominator fractions be added directly?
Yes; combine numerators and keep the denominator.
What is the least common denominator?
The least common multiple of the denominators.
Do mixed numbers work?
Convert to improper fractions or handle whole and fractional parts carefully.