The basic formula: multiply the number by the percentage as a decimal

To find a percentage of a number in Excel, multiply the number by the percentage expressed as a decimal. If you want to know what 20% of 150 is, you enter =150*0.2 in a cell and Excel returns 30. The formula works the same way whether you are calculating a discount, a tax amount, a commission, or any other percentage-based portion of a whole.

You can also write it as =150*20% — Excel understands the percent sign and converts it to a decimal automatically. Both approaches give the same result; use whichever feels clearer to you when you are reading your own spreadsheet later.

Key Takeaways

  • Multiply the base number by the percentage written as a decimal (so 20% becomes 0.2) or use the percent sign directly in the formula.
  • Use cell references instead of typing numbers directly, so you can change the values and the formula updates automatically.
  • When you need the same calculation across many rows, copy the formula down and Excel adjusts the cell references for each row.
  • Use absolute references (with dollar signs) when one cell should stay fixed while others change as you copy the formula down.

Using cell references so your formula updates when numbers change

Instead of typing the actual numbers into your formula, reference the cells where those numbers live. If the base amount is in cell A2 and the percentage is in cell B2, you write =A2*B2. Now when you change the number in A2 or B2, the result updates when ready without you retyping the formula.

This matters because spreadsheets are built for change. You might calculate a 15% discount on a product price today, then realize tomorrow that the discount is actually 18%. With a formula that references cells, you change one number and you are done. With numbers typed directly into the formula, you have to edit the formula itself.

Copying a formula down to calculate percentages for many rows at once

When you have a list of amounts and you want to calculate a percentage of each one, you do not type the formula once for each row. You write it once, then copy it down. Click the cell with your formula, then drag the small square at the bottom-right corner of the cell downward across as many rows as you need. Excel automatically adjusts the cell references for each row.

If your formula in row 2 is =A2*B2, copying it to row 3 makes it =A3*B3, and row 4 becomes =A4*B4. This is called a relative reference — the cell addresses shift as you copy. You can also select the cell and double-click that small square to auto-fill down to the last row with data in the adjacent columns.

Keeping one cell fixed while the other changes (absolute references)

Sometimes you want one number to stay the same while you copy the formula down. Say your tax rate is in cell C1, and you want to calculate tax on amounts in column A for rows 2 through 20. You need the formula to always look at C1, but to look at A2, then A3, then A4, and so on as you copy down.

To lock a cell in place, add dollar signs: =A2*$C$1. The dollar signs mean "do not change this cell reference when I copy the formula." Now when you copy this formula down, A2 becomes A3, A4, A5 and so on, but $C$1 stays $C$1 every time. You can also lock just the column or just the row — $C1 locks the column but lets the row number change, and C$1 locks the row but lets the column change.

Displaying the result as a percentage format instead of a decimal

If your result is 0.2 but you want it to show as 20%, select the cell and click the percent button in the toolbar, or right-click and choose Format Cells. Excel multiplies the displayed number by 100 and adds the percent sign. This is purely how the number looks — it does not change the actual value stored in the cell, so your formulas that use this cell will still work correctly.

Be careful when you format a cell as a percentage before you enter a formula. If you type 20 into a cell formatted as percentage, Excel stores it as 20.00 (or 2000% when displayed), not 0.2. It is usually safer to format the cell after you enter the formula, or to type the decimal yourself.

A real example: calculating a 15% tip on a restaurant bill

You have a bill amount in cell A2 ($48.50) and you want to calculate a 15% tip. In cell B2, you enter =A2*0.15 and Excel shows 7.275, which rounds to $7.28. If you want the result to show as currency, right-click the cell, choose Format Cells, and select Currency. Now it displays as $7.28.

If you have multiple bills in cells A2 through A10 and you want the tip for each one, you enter the formula in B2, then copy it down to B10. Each row calculates 15% of its own bill amount. If the tip percentage changes to 18%, you can either edit the formula in each cell or — better — put the percentage in a separate cell (say D1), write the formula as =A2*$D$1, and copy that down. Now you change only D1 and all the tips recalculate.

Frequently Asked Questions

What is the difference between 20% and 0.2 in an Excel formula?

They are the same thing. Excel converts 20% to 0.2 automatically. You can write =100*20% or =100*0.2 and get the same answer: 20. Use whichever is easier to read in your spreadsheet.

Why does my formula show a decimal instead of a percentage?

The formula calculated correctly — it is just displaying as a decimal. Select the cell and click the percent button in the toolbar, or right-click and choose Format Cells, then select Percentage. The number will display as a percentage without changing the actual value.

How do I calculate what percentage one number is of another?

Divide the first number by the second and format as a percentage. If you sold 45 items out of 200 total, enter =45/200 and format the result as percentage. Excel shows 22.5%, which is the correct answer.

Can I use a formula to calculate a percentage increase or decrease?

Yes. For a percentage increase, use =(new value - old value) / old value. If a price went from $50 to $65, the formula is =(65-50)/50, which shows 0.3 or 30% increase. For a decrease, the formula is the same — it will show a negative percentage if the new value is lower.

What does the dollar sign do in a cell reference like $A$1?

It locks that cell reference so it does not change when you copy the formula to other cells. $A$1 always points to A1. Without the dollar signs, A1 becomes A2, A3, and so on as you copy down. Use dollar signs when you want one cell to stay fixed while others change.