The basic formula: multiply the number by 1 plus the percentage

To add a percentage to a number in a spreadsheet, multiply the original number by 1 plus the percentage as a decimal. If you want to add 20% to 100, the formula is =100*1.20, which gives you 120. The "1" represents the original amount, and the decimal after it (0.20) is the percentage you're adding.

This works the same way in Excel, Google Sheets, LibreOffice Calc, and most other spreadsheet programs. The formula structure stays consistent: original number, times, 1 plus the percentage in decimal form.

Key Takeaways

  • The formula to add a percentage is =number*1.percentage as a decimal, so adding 15% to 80 is =80*1.15.
  • You can reference a cell instead of typing the number directly, like =A1*1.20 to add 20% to whatever is in cell A1.
  • To make the percentage itself a cell reference, use =A1*(1+B1) where B1 contains the percentage as a decimal (0.20 for 20%).
  • Copying the formula down a column applies the same calculation to multiple rows at once, which is faster than entering it separately each time.

Using cell references instead of typing numbers directly

Instead of putting the number into the formula itself, you can reference a cell. If the number 100 is in cell A1 and you want to add 20% to it, type =A1*1.20 in another cell. The spreadsheet reads the value in A1, multiplies it by 1.20, and shows the result.

This becomes useful when you have a list of numbers and want to add the same percentage to all of them. You enter the formula once, then copy it down the column. Each row automatically adjusts to use the number in its own A cell.

Making the percentage itself a cell reference

If the percentage you're adding changes or you want to store it separately, put the percentage in its own cell as a decimal. If cell B1 contains 0.20 (which represents 20%), the formula becomes =A1*(1+B1). This multiplies the number in A1 by 1 plus the decimal in B1.

This setup is helpful when you're working with multiple percentages or when the percentage might change. You can update the value in B1 once, and every formula that references it recalculates automatically. You can also use this same formula across different rows if each row has its own percentage in a different cell.

Copying the formula down to multiple rows

When you have a column of numbers and want to add the same percentage to each one, enter the formula in the first row, then copy it down. Click the cell with your formula, then drag the small square at the bottom-right corner of the cell down as far as you need. The spreadsheet adjusts the cell references automatically for each row.

If your formula is =A1*1.20 in row 1, copying it to row 2 makes it =A2*1.20, row 3 becomes =A3*1.20, and so on. This saves time and reduces the chance of typing errors when you're working with dozens or hundreds of numbers.

Converting percentages that are already written as numbers

Sometimes a percentage appears in a cell as "20" instead of "0.20". If that's the case, divide it by 100 first. The formula becomes =A1*(1+(B1/100)), where B1 contains 20. The /100 converts 20 into 0.20, then the rest of the formula works as usual.

You can also use this approach if you're typing the percentage directly: =A1*(1+(20/100)) adds 20% to the number in A1. Both methods give the same result — use whichever matches how your data is already formatted.

Checking your work with a straightforward example

Test your formula with math you can verify by hand. If you're adding 10% to 50, the answer should be 55. In the spreadsheet, enter =50*1.10 and confirm it shows 55. If you're adding 25% to 80, the answer is 100 — enter =80*1.25 and check.

Once you see the formula working correctly on a straightforward example, you can trust it when you explore it to larger numbers or longer lists. This takes 30 seconds and catches mistakes before they affect your whole spreadsheet.

When to use a formula versus calculating it once

Use a formula when the numbers or percentages might change later, or when you have many rows to calculate. Use a one-time calculation (or just type the final number) when you're adding a percentage to a single number that won't change and you don't need to show your work.

If you're building a budget or a price list that you'll update regularly, formulas save time and reduce errors. If you're just figuring out what 20% more than 150 is for a one-off question, typing =150*1.20 into any spreadsheet takes five seconds and you're done.

Frequently Asked Questions

What's the difference between adding a percentage and multiplying by a percentage?

Adding 20% to 100 means the result is 120 (the original 100 plus 20 more). Multiplying 100 by 20% means the result is 20 (just the percentage itself). Adding uses 1 plus the percentage; multiplying uses only the percentage. The formula =A1*1.20 adds; the formula =A1*0.20 multiplies.

Can I add different percentages to different rows?

Yes. Put each percentage in its own cell, then use the formula =A1*(1+B1) where B1 is the percentage for row 1. Copy the formula down, and it will automatically reference B2 for row 2, B3 for row 3, and so on. Each row uses its own percentage.

What if I want to subtract a percentage instead?

Use 1 minus the percentage instead of 1 plus. To subtract 15% from 100, the formula is =100*0.85 (or =100*(1-0.15)). This gives you 85. The structure is the same; you just change the plus sign to a minus sign.

Does the formula work the same in Google Sheets as in Excel?

Yes. The basic formulas =A1*1.20 and =A1*(1+B1) work identically in Excel, Google Sheets, LibreOffice Calc, and most other spreadsheet programs. The syntax is the same, and copying formulas down works the same way across all of them.