The three ways to calculate percentages in Excel

Excel handles percentages in three main ways: as a formula that divides one number by another, as a format that displays a decimal as a percentage, or as a percentage increase or decrease between two values. Which one you use depends on what you're trying to show — whether you're converting raw numbers into percentages, displaying existing decimals as percentages, or tracking how much something changed.

The most common task is turning a part-to-whole relationship into a percentage. If you have 45 people out of 200, you write =45/200 in a cell and Excel gives you 0.225. Then you format that cell as a percentage and it displays as 22.5%. The formula does the math; the format does the display.

The second task is showing percentage change — how much a number grew or shrank. If sales were 1000 last month and 1200 this month, you calculate =(1200-1000)/1000 to get 0.2, which formats as 20% growth. This formula works the same way whether the number went up or down.

Key Takeaways

  • A percentage formula divides the part by the whole: =45/200 gives you the decimal 0.225, which you then format as a percentage to show 22.5%.
  • To show percentage change between two numbers, use =(new-old)/old, so a change from 100 to 120 becomes =(120-100)/100 and displays as 20%.
  • Format a cell as a percentage by right-clicking it, choosing Format Cells, and selecting Percentage from the Category list.
  • You can also multiply a decimal by 100 and add a % symbol manually, but using Excel's percentage format is cleaner and updates automatically if the numbers change.

Converting a decimal to percentage format

Once you have a decimal in a cell — whether from a formula like =45/200 or a number you typed in like 0.225 — you need to tell Excel to display it as a percentage. Right-click the cell and select Format Cells. In the window that opens, click the Number tab if it is not already selected, then click Percentage in the Category list on the left. Click OK.

Excel will multiply the decimal by 100 and add a % sign. So 0.225 becomes 22.5%, and 0.5 becomes 50%. If you want to control how many decimal places show — for example, 22.50% instead of 22.5% — you can type a number in the Decimal places field before clicking OK. Most of the time, one or two decimal places is enough.

You can also use the percentage button in the toolbar. Select the cell or cells you want to format, then click the % button in the ribbon at the top. Excel applies the percentage format when ready. This is faster than right-clicking, but it uses whatever decimal-place setting Excel has as default — usually two places.

Building a formula for part-to-whole percentages

The simplest percentage formula divides a part by a whole. If you are tracking how much of a budget you have spent, how many survey respondents chose one answer, or what fraction of your inventory is in stock, you use this structure: =part/whole.

Put the part in one cell and the whole in another. Let's say cell A2 holds 45 (the part) and cell B2 holds 200 (the whole). In cell C2, type =A2/B2 and press Enter. Excel calculates 0.225. Then format C2 as a percentage and it shows 22.5%. If the numbers in A2 or B2 change later, the percentage updates automatically.

You can also write the formula with the numbers directly: =45/200. This works, but using cell references (like A2 and B2) is better because you can change the numbers without rewriting the formula. If you have many rows of data, you can write the formula once in C2, then copy it down to C3, C4, and so on. Excel adjusts the cell references for each row.

Calculating percentage change or growth

Percentage change tells you how much a number grew or shrank compared to where it started. The formula is =(new value - old value) / old value. If your sales were 1000 last month and 1200 this month, the change is =(1200-1000)/1000, which equals 0.2 or 20% growth. If sales dropped to 800, the formula gives =(800-1000)/1000, which equals -0.2 or -20% — the negative sign shows a decrease.

Set up your spreadsheet with the old value in one column and the new value in another. If the old value is in A2 and the new value is in B2, write =(B2-A2)/A2 in cell C2. Format C2 as a percentage. Now you can see at a glance whether the number went up or down and by how much.

This formula works for any comparison where you want to know the rate of change: revenue from one quarter to the next, website traffic from one month to the next, or test scores before and after a training program. The structure stays the same — subtract the starting point from the ending point, then divide by the starting point.

Using percentages in larger calculations

Once you have a percentage in a cell, you can use it in other formulas. If cell C2 holds 22.5% (the result of =A2/B2), and you want to know what 22.5% of 500 is, you write =C2*500. Excel multiplies 0.225 by 500 and gives you 112.5. The percentage format does not change how Excel does math — it is just a display choice.

You can also calculate a percentage of a number directly without storing the percentage first. If you want 15% of 200, write =200*0.15 or =200*15%. Both give you 30. The second version is easier to read because it shows your intent clearly — you are taking 15% of something.

A common task is adding a percentage increase to a number. If an item costs 100 and you want to mark it up by 20%, the new price is =100+(100*0.20) or =100*1.20. The second formula is shorter: multiply the original by 1 plus the percentage increase. For a 20% markup, multiply by 1.20. For a 15% discount, multiply by 0.85 (which is 1 minus 0.15).

Common mistakes and how to avoid them

The most common mistake is forgetting to format the cell as a percentage after writing the formula. You get a decimal like 0.225 and think something is wrong, when really you just need to explore percentage formatting. Remember: the formula creates the number, and the format displays it the way you want to see it.

Another mistake is mixing up the order in a percentage-change formula. The denominator (the bottom number) must always be the old or starting value, not the new one. If you write =(old-new)/new instead of =(new-old)/old, your percentage will be backwards. Write it out in words first if you are unsure: "new minus old, divided by old."

A third mistake is using the wrong cell reference when you copy a formula down. If you write =A2/B2 in C2 and copy it to C3, Excel automatically changes it to =A3/B3, which is what you want. But if you meant B2 to stay the same (because it is a total that does not change), you need to lock it with dollar signs: =A2/$B$2. Then when you copy down, it becomes =A3/$B$2, keeping B2 fixed.

Displaying percentages with decimal places and rounding

By default, Excel's percentage format shows two decimal places. So 0.225 displays as 22.50%, and 0.1 displays as 10.00%. If you want fewer or more decimal places, right-click the cell, choose Format Cells, select Percentage from the Category list, and change the number in the Decimal places field. Setting it to 0 shows 22% and 10%. Setting it to 3 shows 22.500% and 10.000%.

Changing the decimal-place setting does not change the actual number in the cell — it only changes how Excel displays it. If a cell contains 0.225 and you format it to show 0 decimal places, it displays as 22% but the underlying value is still 0.225. If you use that cell in another formula, Excel uses 0.225, not 22.

If you need to round a percentage to a whole number for display purposes, you can use the ROUND function. =ROUND(A2/B2,2) calculates the percentage and rounds it to 2 decimal places. Then format the result as a percentage. This is useful when you want to control rounding separately from formatting.

Frequently Asked Questions

What is the difference between formatting as a percentage and multiplying by 100?

Formatting as a percentage tells Excel to display a decimal as a percentage automatically. Multiplying by 100 and adding a % symbol manually gives you a number like 22.5 with a % next to it, but Excel treats it as text, not a number. Use formatting — it is cleaner and lets you use the percentage in other calculations.

Can I add percentages together?

You can add the numbers that are displayed as percentages, but the result depends on what they represent. If 22% and 15% are both parts of the same whole, adding them gives 37%. But if they are percentages of different wholes, you have to convert them back to their original numbers first, add those, then calculate the new percentage. Adding percentages only works when they share the same denominator.

How do I show a percentage increase or decrease in red or green?

Select the cells with your percentage-change formulas, right-click, and choose Format Cells. Click the Number tab, select Percentage from the Category list, then look for a format in the list that shows negative numbers in red. Click it and then OK. Now negative percentages (decreases) display in red and positive ones in black.

What if my percentage comes out to more than 100%?

That is fine — it just means the part is larger than the whole. If you sold 150 units this month and 100 last month, the percentage change is 50%. If a project budget is 100 and you spent 150, you are at 150% of budget. Excel displays it normally; there is nothing wrong with a percentage over 100%.

Can I use a percentage directly in a formula without converting it to a decimal?

Yes. You can write =200*15% and Excel understands that 15% means 0.15. You can also write =200*0.15 — both give the same result. Using the % symbol makes the formula easier to read, especially when you are calculating a discount or markup.