In order to add or subtract fractions with different denominators, you need to find the lowest common denominator (LCD). The LCD is the lowest number that can be a common denominator for all the fractions. One way to find the LCD is to list the multiples of each denominator and then find the lowest multiple which is common to all denominators. For some problems, this can be tedious and time consuming. This calculator does it for you.

To use this calculator enter the denominators of two or three fractions. Leave out any negative sign or commas. After finding the LCD, you need to divide it by the original denominator to find out what factor to multiply the numerator by so the fractions value remains the same. Then you can add or subtract the fractions as required.

The lowest common denominator is also known as the least common denominator (LCD) or the lowest common multiple (LCM).

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