Percentage Calculator Excel Formula

This page explains the core Excel formulas for calculating percentages: part/total, percentage change, and percentage of a total. You enter the numbers in cells, and Excel returns the percentage as a decimal or a formatted percent value. The formulas work in all modern versions of Excel and Google Sheets.

Formula

The basic percentage formula is:

Percentage = (Part / Total) × 100

In Excel, if you put the part in cell A1 and the total in cell B1, the formula is:

=A1/B1

Excel displays the result as a decimal (e.g., 0.125). To show it as a percentage, format the cell with the Percent Style button (Home tab > Number group) or press Ctrl+Shift+%. The cell then shows 12.5%.

For percentage change between two numbers (old value in A1, new value in B1):

=(B1-A1)/A1

Format as percent to see the change. A positive result is an increase, a negative result is a decrease.

Worked Example

Using the default values from the calculator: Part = 25, Total = 200.

1. Divide the part by the total: 25 ÷ 200 = 0.125
2. Multiply by 100 to get the percentage: 0.125 × 100 = 12.5%

The calculator shows 12.5% as the headline answer, matching the Excel formula =A1/B1 with formatting.

How to Write a Percentage Formula in Excel

Enter your numbers in cells, then type the formula in another cell. For example:

• In cell A1, type 25 (the part).
• In cell B1, type 200 (the total).
• In cell C1, type =A1/B1 and press Enter.
• Select cell C1, then click the Percent Style button in the Number group on the Home tab. Excel shows 12.5%.

If you want the result as a plain number (e.g., 12.5 without the % sign), use =A1/B1*100 and format as Number.

Common Percentage Formulas in Excel

Here are the most useful variations:

• Part of a total: =part/total – format as percent.
• Percentage change: =(new-old)/old – format as percent.
• Percentage of a column total: =A2/SUM($A$2:$A$10) – copy down.
• Increase a number by a percentage: =number*(1+percent) – e.g., =100*(1+0.15) gives 115.
• Decrease a number by a percentage: =number*(1-percent).

How to Choose the Right Formula

Ask yourself what you are trying to find:

• If you have a part and a whole, use part/total.
• If you have an old value and a new value, use (new-old)/old for change.
• If you want to add a percentage (like tax or tip), use number*(1+percent).
• If you want to subtract a percentage (like a discount), use number*(1-percent).

Common Mistakes and How to Avoid Them

The most frequent error is forgetting to format the result as a percentage. If you see 0.125 instead of 12.5%, the formula is correct but the cell is not formatted. Another mistake is mixing up the part and the total, which gives a wrong answer (e.g., 200/25 = 800%). Also, be careful with percentage change: the formula is (new-old)/old, not new/old. The latter gives a ratio, not a change.

Rounding can also cause confusion. Excel stores more decimal places than it shows, so a displayed 12.5% might actually be 12.53%. Use the ROUND function if you need exact values: =ROUND(A1/B1,4).

Percentage Formatting in Excel

Excel’s Percent Style multiplies the cell value by 100 and adds a % sign. If you type 12.5 and format as percent, it shows 1250%. To avoid that, either type the decimal (0.125) or use a formula that divides by 100. The safest approach: keep the raw decimal in the cell and apply percent formatting.

Alternatives to Excel for Percentages

If you do not have Excel, Google Sheets uses the same formulas. LibreOffice Calc also works identically. For quick one-off calculations, the calculator at the top of this page gives the same result without needing to set up a spreadsheet. Many online percentage calculators also handle change and increase/decrease, but they often do not show the underlying formula.

Frequently Asked Questions

How do I calculate a percentage of a total in Excel?

Divide the part by the total and format as percent. For example, =A1/B1 where A1 is the part and B1 is the total. Then apply Percent Style.

Why is my Excel percentage showing as a decimal?

The cell is not formatted as a percentage. Select the cell, go to Home > Number and click the % symbol. Excel will multiply by 100 and add the % sign.

How do I calculate percentage change between two numbers in Excel?

Use =(new-old)/old. For example, if old is in A1 and new is in B1, type =(B1-A1)/A1 and format as percent.

How do I add a percentage to a number in Excel?

Multiply the number by 1 plus the percentage. For a 15% increase: =100*(1+0.15) gives 115. For a discount, use =100*(1-0.15) gives 85.

Can I use the same formulas in Google Sheets?

Yes. Google Sheets uses the same syntax and formatting. The percent format is under Format > Number > Percent.

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in a | Part | - | 25 | 0
in b | Total | - | 200 | 0
out pct | Part as % of total | % | (a / b) * 100 | 2
out ratio | Part per 1 of total | - | a / b | 4