To find a percentage of a number: `=A1*10%`
To calculate percentage as part of a whole: `=A1/B1`
To convert a decimal to a percentage: `=A1*100`
To calculate percentage increase: `=(New Value-Old Value)/Old Value`
To calculate percentage decrease: `=(Old Value-New Value)/Old Value`
To get the percentage difference between two values: `=ABS(A1-B1)/AVERAGE(A1,B1)`
To format a cell as a percentage: select the cell and click `%` on the Home tab
To calculate what percent one number is of another: `=Part/Total`
To increase a number by a percentage: `=A1*(1+B1)`
To decrease a number by a percentage: `=A1*(1-B1)`