Use the formula: `=(New Value-Old Value)/Old Value`
Format the result cell as Percentage
Example: `=(B2-A2)/A2`
If Old Value is in `A2` and New Value is in `B2`, enter `=(B2-A2)/A2`
Multiply by 100 only if you are not using percentage formatting: `=((B2-A2)/A2)*100`
To avoid errors when Old Value is zero, use: `=IF(A2=0,””,(B2-A2)/A2)`
For a decrease, the result will be negative
For improvement percentage, use the same formula and interpret positive values as improvement