1. Diagnosis Your formula divides the change by the new value (B2), but percent change must be divided by the old value (A2). 2. The formula =(B2-A2)/A2 3. How it works B2-A2 gives the change: new value minus old value. /A2 divides that change by the starting value, so the result shows how big the change is compared with where you began. Format the cell as Percentage (Home tab, Number group, % button) so 0.25 displays as 25%. 4. Test on your sample Row 2: (100-80)/80 = 20/80 = 0.25, which shows as 25%. Row 3: (150-200)/200 = -50/200 = -0.25, which shows as -25% (a decrease). Your original formula gave 20/100 = 20% for row 2, which is why it did not match your expectation. 5. Why this goes wrong Percent change always asks "how much did it change compared with the starting point?" The starting point is the old value, so it must be the divisor. Dividing by the new value is a very common slip because B is the value you are looking at most. A quick check: if the old value is 80 and you add 25% of 80 (which is 20), you land on 100, so 25% is correct. 6. If you use an older version Not relevant here. This formula works in every version of Excel. If your regional settings use semicolons as separators, the formula stays the same because it has no commas.