Key points

• A percentage is best entered and stored in a spreadsheet as a decimal fraction. In most spreadsheets this happens automatically if you enter a value followed by a % sign. You can also set a percentage display format to show decimal fractions as percent. That is entering 33% stores 0.33 in a cell and setting the display format to percent makes it display as 33%.

• If a percentage is stored as a decimal fraction you can work out that percentage of another value simply by multiplying.

• • To increase a quantity by I% multiply by (1+I)
  • To decrease a quantity by I% multiply by (1-I)
  • To recover a value that has been increased by I% divide by (1+I) and to recover a value that has been decreased by I% divide by (1-I)

• Finding P% of a quantity and then Q% of the result is not the same as finding (P+Q)% of the original value.
• In the same way increasing/decreasing a value by P% and then increasing/decreasing it by Q% is not the same as increasing/decreasing it by (P+Q)%..
• Using a negative percentage to mean a percentage decrease simplifies most formulas involving percentages.
• Percentage increases/decreases maintain existing ratios but change absolute differences in size.

More Financial Functions:

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