Percentage Change Made Simple: Increase, Decrease, and th…

I’ve written about percentages for ten years. Even now, I still see smart people – like finance analysts, marketing managers, and even teachers – quietly mix up “percentage increase” and “percentage points.” It’s a mistake that’s easy to miss. But then you see a headline like “inflation jumped 25%,” when what they really mean is “inflation went from 8% to 10%.” These are two totally different stories. They mean two totally different numbers.

This is the article I wish I’d read in middle school. Bookmark our percentage calculator for quick checks. We’re going to cover every type of percentage change you’ll ever need. I’ll include examples, common mistakes, and a cheat sheet at the end.

What “percentage change” really means

At its heart, percentage change asks one simple question: How much did something grow or shrink compared to where it started? The math formula is the same everywhere:

Percentage change = ((New value − Old value) / Old value) × 100

Here are three rules to help you avoid common errors:

• The number at the bottom (the denominator) is always the first value, not the new one.
• If your answer is a positive number, it means a percentage increase. If it’s negative, it’s a percentage decrease.
• “Increase” and “decrease” don’t always work the same way. I’ll explain this more later on.

A quick example

Let’s say you bought 100 shares of a stock for $50 each. Now, each share is worth $62.

• (62 − 50) / 50 = 0.24
• 0.24 × 100 = 24% increase

If a coworker says “it went up 24 dollars per share,” they are correct about the exact dollar amount. But the percentage change shows how big that move is compared to your starting price.

Percentage increase: the most common type

You use this when the new value is larger than the old one.

Percentage increase = ((New − Old) / Old) × 100

Here are some real-life examples:

Percentage decrease: where people often get confused

You use this when the new value is smaller than the old one.

Percentage decrease = ((Old − New) / Old) × 100

A common mistake happens in stores. Imagine a jacket is first $200, then it’s on sale for $150. The discount is:

• (200 − 150) / 200 = 0.25
• = 25% off

If you do the math backward and divide by the new price by mistake, you’d get 33.3%. This 33.3% is the percentage increase you’d need to go from $150 back to $200. It’s a completely different number. This shows the asymmetry I mentioned earlier. A 25% drop and a 25% rise don’t cancel each other out:

To fully get back to the original price after a 25% drop, you need a 33.3% rise. This is why a stock that drops 50% needs to go up 100% just to break even.

Percentage points vs. percentage change

This difference confuses news anchors every week. Let’s say the central bank raises interest rates from 4% to 5%. There are two correct ways to talk about this:

• It’s a 1 percentage point increase.
• It’s a 25% increase (because 1 ÷ 4 = 0.25).

If a reporter writes “interest rates climbed 25% this week,” they are technically right. But they will scare every homeowner reading that headline. Both ways of saying it are correct. The problem comes from mixing them up. This same trap appears with inflation, election results, and mortgage rates – anytime you compare two percentages.

The reverse problem: “X% of Y is Z, what is Y?”

This is the second most helpful percentage trick. It’s especially good for sales and managing your money.

Find the original price from a sale price

You paid $54 for a shirt that was 40% off. What was the original price?

• $54 is 100% − 40% = 60% of the original price.
• Original price = 54 / 0.60 = $90.

Find the original price before tax

Your receipt total is $108.50. Sales tax in that area is 8.5%. What was the price before tax?

• 108.50 / 1.085 = $100.

The key here is always to divide, not subtract. You can double-check your work with our sales tax calculator.

Percentage change with negative numbers (a special situation)

What if the starting value was negative? Imagine a company lost $50,000 last year. This year, they made a $10,000 profit. Did they improve by 120%? By 80%? Or something else?

The basic percentage change formula doesn’t work well here because the number at the bottom would be negative. Most analysts use absolute values (the number without its minus sign):

((New − Old) / |Old|) × 100

So: (10,000 − (−50,000)) / |−50,000| = 60,000 / 50,000 = 120% improvement.

You might hear this described as “the company went from losing money to making a profit.” That’s a good way to explain it to people who don’t need the exact numbers.

Real-world mistakes to avoid

• Two sales discounts don’t just add up. If something is 30% off, then an extra 20% off, it’s not 50% off. You get 30% off the original price, then 20% off that new, lower price. That means a total of 44% off.
• “Average” percentages can be tricky. If you gain 10% on an investment one year and lose 10% the next, your average return isn’t 0%. It’s actually -1% because of how compounding works.
• “Up to X% off” usually has small print. That big discount almost never applies to everything. Always read the details.
• Year-over-year (YoY) vs. Month-over-month (MoM) growth. If something grows 5% each month (MoM) for 12 months, that’s roughly 80% growth for the year (YoY), not 60%.
• Rounding with small starting numbers. Going from 1 customer to 2 customers is a 100% increase. But it’s such a small change, it might not mean much.

Cheat sheet: every percentage formula in one place

How you can use percentages in real life

Finance

Think about stock returns, how your salary changes, interest rates, inflation, sales tax, mortgage points, or figuring out a tip. Use the tip calculator when you’re at a restaurant. For long-term money plans, try the compound interest calculator.

Health

Percentages help with your body fat percentage, how much weight you lift compared to your max, your calorie deficit (like your TDEE × 0.85), and heart rate zones. Combine our TDEE calculator with a percentage calculator to plan a weight loss phase.

Marketing & analytics

Conversion rates, click-through rates (CTR), how many customers leave (churn), and growth each month or year (MoM and YoY) are all based on percentages. Always show the starting number too. A 200% increase from 2 visitors a day to 6 isn’t a big deal.

Frequently asked questions

How do I calculate percentage change in Excel or Google Sheets?

Type =(B1-A1)/A1 and then set the cell to show as a percentage. Or, for a simpler way, use =B1/A1-1. Both give you the same answer.

What is the difference between percentage and percentile?

A percentage is a part out of 100. A percentile shows your rank in a list of data. For example, the 90th percentile means 90% of the other values are lower than yours. They sound similar, but they are very different in math.

How do I calculate the percentage of two numbers?

If you mean “what percentage is A of B,” use the formula (A / B) × 100. If you mean the percentage change between them, use ((B − A) / A) × 100. You can put both into our percentage calculator to see them side-by-side.

Why does “averaging” two percentages give the wrong answer?

This is because percentages depend on their starting point. A 50% gain followed by a 50% loss won’t cancel out. To correctly average percentage returns over time, you should use the geometric mean, not the regular average.

Can a percentage be more than 100%?

Yes, absolutely! A new company whose sales triple in a year grew by 200%. If your workout doubles your maximum bench press, that’s a 100% increase. “Percentage” just means “per hundred.” There’s no upper limit unless the thing you’re measuring has one (you can’t be 110% pregnant!).

Wrapping up

Percentages are easy to learn, but truly mastering them takes time. The formula rarely changes. The real challenge is understanding what the numbers mean. Spend ten minutes with the CalcaTools percentage calculator. Go through every item on the cheat sheet above. You’ll stop confusing percentage points with percentage change. This small bit of clarity can save you money on bad sales, prevent awkward moments in meetings, and even help you avoid an argument about who tipped more at dinner.

Related calculators and guides

More percentage and math tools:

• Percentage Calculator — helps with all three types of percentage problems.
• Percent Error Calculator — compare what you measured to the real value.
• Sales Tax 101 — how to add and remove sales tax.