Watch Simplifying fractions. You can simplify a fraction if the numerator (top number) and denominator (bottom number) can both be divided by the same number. Six twelfths can be simplified to Fractioncalculator. Input fractions. . This calculator subtracts two fractions. First, convert all fractions to a common denominator when fractions have different denominators. Find Least Common Denominator (LCD) or multiply all denominators to find a common denominator. When all denominators are the same, simply subtract the JTabXW.