How to Calculate Percentage Increase and Decrease: Formula and Examples

This guide goes beyond the formula. It covers the points that trip people up in real reports: percentage points versus percent change, back-to-back changes, and zero or tiny starting values. For a quick answer, keep our percentage calculator open in another tab and check each worked example against it.

We are Talha Aslan and team, and we read advertising and SEO reports with our clients every month. That is why every example here uses real marketing metrics such as click-through rate, orders, and conversion rate. Also, all numbers are worked examples. Simply follow the same steps with your own data.

What is the percentage increase formula, step by step?

The formula has four steps, and the order matters. If you swap the subtraction and the division, the answer changes completely. So take the difference first, then divide.

1. Write down the old (starting) value and the new (ending) value. In this worked example, the old value is 320 orders and the new value is 368 orders.
2. Subtract the old value from the new value: 368 - 320 = 48. We also call this the absolute change.
3. Divide the absolute change by the old value: 48 / 320 = 0.15.
4. Multiply by 100: 0.15 × 100 = 15. So orders rose by 15%.

Skipping the fourth step is a common slip. A spreadsheet cell that reads 0.15 can look like 0.15% to a busy reader. On the other hand, when you format a cell as a percentage, the spreadsheet multiplies by 100 for you. If you also multiply inside the formula, the cell shows 1,500%. In short, multiply in the formula or in the format, never both.

Here is the one-line version: percent change = (new - old) / old × 100. In other words, percentage increase and percentage decrease come from the same formula; only the sign of the result differs. Therefore you never need to memorize two formulas.

How do you calculate a percentage decrease correctly?

You use the same formula for a decrease. The only difference is that the new value is smaller, so the result comes out negative. For example, if monthly organic clicks fell from 450 to 396, the change is -54. Then -54 / 450 × 100 gives -12, which is a 12% decrease.

The classic mistake, however, is to divide the drop by the new value. That gives 54 / 396, roughly 0.136, and a wrong answer of 13.6%. However, a decrease always uses the starting value as its base.

There is also an asymmetry to keep in mind. Going from 200 to 250 is a 25% increase. Going back from 250 to 200, however, is a 20% decrease. The gap is the same 50 units, but the bases differ, so the percentages differ too. As a result, the sentence "we fell 20% last month and grew 20% this month, so we are back where we started" is simply wrong.

Finally, a positive metric can drop by 100% at most. So if the value hits zero, that is a 100% decrease. If a report shows a 120% decrease, look for an error in the base or the sign.

Which number is the old value and which is the new one?

The old value in the formula is your reference point. In time comparisons, it is usually the earlier period: last month, last week, or the same month last year. Yet if you pick the wrong reference, the math can be right while the interpretation is wrong. Marketing reports typically rely on three reference points:

• Previous period: you compare this month with last month. It is great for quick reactions, but it hides seasonality.
• Same period last year: you compare November with last November. This largely neutralizes seasonal swings.
• Target: you compare actual results with the plan. In this case, the target takes the place of the old value.

Example scenario: thanks to a holiday sale, traffic in November rose 40% over October. Compared with last November, though, the increase was only 6%. Both numbers are correct, but they answer different questions. That is why every percentage in a report should state its comparison period.

Also make sure both periods have the same length. If you compare a 31-day month with a 28-day month, roughly 10% of the gap in totals comes from the extra days alone. In that case, comparing daily averages gives a fairer picture.

What is the difference between percent and percentage points?

A percentage point is the plain subtraction between two percentages. Percent change, by contrast, measures that gap relative to the starting rate. People mix the two up constantly with rate metrics such as click-through rate, conversion rate, and bounce rate.

Worked example: your conversion rate went from 2% to 3%. In percentage points, the increase is 3 - 2 = 1 point. As a percent change, it is (3 - 2) / 2 × 100, a 50% increase. Both statements are therefore true. Still, "conversion rate rose 1%" is ambiguous, because a reader could take it to mean 2% became 2.02%.

The clearest way to write it is: "Conversion rate rose from 2% to 3% (+1 percentage point, a 50% relative increase)." Giving both figures leaves no room for misreading. We follow this convention in every report for exactly that reason.

The same rule also applies to declines. If bounce rate dropped from 60% to 45%, that is a fall of 15 points, or 25% in relative terms. Then choose which figure to headline based on the question your reader is asking.

How should you report a change in click-through rate (CTR)?

Click-through rate (CTR) is the number of clicks divided by the number of impressions. The CTR definition in Google Ads Help gives the same formula: clicks ÷ impressions. So a change in CTR is a change in a rate, and the point-versus-percent rule applies here too.

Worked example: last month a campaign had 20,000 impressions and 600 clicks, a CTR of 3.0%. Then this month it had 25,000 impressions and 900 clicks, a CTR of 3.6%. The CTR change is +0.6 points. In relative terms, (3.6 - 3.0) / 3.0 × 100 is a 20% increase.

Notice that this example contains three different percentage increases. Impressions rose 25%, clicks rose 50%, and CTR rose 20%. Indeed, 1.25 × 1.20 = 1.50, which shows the three figures are consistent. The jump in clicks came from both more visibility and a more appealing result.

For a quick check, use our CTR calculator. If you want to know what moves CTR on the organic side, our guide on how to improve organic CTR covers it in detail.

Why don't back-to-back increases and decreases cancel out?

You never add consecutive percentage changes; you multiply them. This is the rule people miss most often in reports. After all, our intuition treats percentages like fixed amounts.

Worked example: a site with 1,000 sessions grows 20% and then shrinks 20%. After the first month, it has 1,000 × 1.20 = 1,200 sessions. After the second month, it drops to 1,200 × 0.80 = 960 sessions. So the result is not a return to the start; it is a 4% loss.

The reason is simple. In practice, the second percentage applies to the new, larger base. The 20% increase works on a small base, while the 20% decrease works on a bigger one. As a result, the decrease takes away more than the increase added.

You can use the same logic to find the increase needed to recover. A metric that fell 20% must rise 25% to get back, since 0.80 × 1.25 = 1. A metric that fell 50% must rise 100%.

The general formula is: required increase = size of the drop / value after the drop × 100. For instance, a metric that fell from 1,000 to 800 needs 200 / 800 × 100, a 25% increase. Our percentage calculator also shows this recovery figure as an extra row in its Percent change mode.

How do you find the total percentage increase over several periods?

Turn each period's percentage into a multiplier, then multiply the multipliers together. For an increase, add the percentage to 1, so a 10% increase becomes 1.10. For a decrease, subtract it from 1, so an 8% decrease becomes 0.92.

1. Convert each period's percentage into a multiplier.
2. Multiply all the multipliers together.
3. Subtract 1 from the product and multiply by 100. That figure is the total change.

Worked example: an email list that grows 10% three months in a row grows 33.1% in total, not 30%. That is because 1.10 × 1.10 × 1.10 = 1.331. You solve a mixed series the same way.

For example, a 15% increase, an 8% decrease, and a 5% increase give 1.15 × 0.92 × 1.05 = 1.1109. In other words, the total change is roughly an 11.1% increase. Simple addition (15 - 8 + 5 = 12) lands close here. However, the gap widens as the number of periods and the size of the rates grow.

So do not stack monthly percentages and call the sum annual growth. Instead, plug the values from the start and the end of the year straight into the formula. It is both shorter and more accurate.

How do you find the average percentage increase per period?

When you know the total change over several periods, you find the average per period with the geometric mean, not the arithmetic mean. Put simply, you take the nth root of the total multiplier, where n is the number of periods.

Worked example: monthly sessions went from 1,000 to 1,440 in two months. The total increase is 44%. The monthly average, however, is 20%, not 22%, because the square root of 1.44 is 1.20. You can verify it quickly: 1,000 × 1.20 = 1,200, then 1,200 × 1.20 = 1,440.

The earlier example shows why the arithmetic mean misleads. For instance, the arithmetic average of +20% and -20% is zero, yet the real outcome was a 4% loss. The geometric mean starts from the product 0.96 and shows a loss of about 2% per period.

For more than two periods, use the power function on your calculator and raise the total multiplier to the power of 1/n. This average helps when you need to compare growth speed across periods of different lengths. For example, it lets you compare a three-month campaign with a six-month one.

How do you work back to the original value after a percentage change?

If you only have the new value and the percentage, divide by the multiplier. The formula is: old value = new value / (1 + percent / 100). For a decrease, use 1 - percent / 100 in the denominator instead.

Worked example: a report says this month's orders reached 138, up 15% on last month. Last month's orders were 138 / 1.15 = 120. A common mistake is to take 15% of 138 (20.7) and subtract it, which gives 117.3. That answer is wrong, because the 15% increase sat on a base of 120, not 138.

The same logic helps with target setting. Example scenario: you received 400 form submissions last quarter and want a 25% increase. The target is 400 × 1.25 = 500 submissions. Then you track progress with actual / target × 100; at 450 submissions you have reached 90% of the target.

Working back from a sale price to the list price is another version of this reverse calculation. We cover that one separately in our guide on how to calculate a discount percentage.

How do you check a percentage increase with a calculator?

Checking a manual result a second way catches most report errors before they reach a meeting. That is why our team calculates every important figure twice, using two different methods. A calculator check takes only a few seconds:

1. Open the percentage calculator and press "Percent change" in the top bar.
2. Type the old value in the first field and the new value in the second. For the worked example, enter 320 and 368.
3. Read the large result. A plus sign means an increase and a minus sign means a decrease; here you will see a 15% increase.
4. If you want the reverse direction, press the Swap button. The same two numbers then show the change the other way.
5. Compare the result with your manual answer. If they differ, check the base first and then the order of the values.

The calculator reads numbers the English way, so 10,000 means ten thousand and 1.5 means one and a half. In addition, when the old value is negative, it uses the absolute value in the denominator. We explain that detail in the section on negative values below.

Worked examples table for marketing metrics

The table below shows worked examples for metrics we often see in a monthly marketing report. For count metrics, the fourth column shows the absolute change. For rate metrics, it shows the change in percentage points. That way you can see at a glance which wording each row needs.

The row that deserves attention is conversion rate. A half-point drop looks small, yet in relative terms it is a 20% loss. Meanwhile, sessions rose 15%, so total conversions fell by about 8%, since 1.15 × 0.80 = 0.92.

Can you calculate a percentage increase from zero?

No. When the old value is zero, the formula divides by zero, and the percent change has no meaningful value. For example, if a new campaign had 0 conversions last month and 40 this month, writing "infinite growth" or inventing a percentage makes no sense. Instead, you have three honest options:

• State the absolute change: "Conversions went from 0 to 40."
• Use a longer baseline and take the campaign's first full month as the reference.
• Use a share instead of a change: "8% of all conversions came from the new campaign."

In spreadsheets, this usually shows up as a divide-by-zero error. If you write the formula so that it leaves the cell blank or prints "new" when the old value is zero, the table stays clean and nobody gets misled.

A similar trap appears when the old value is close to zero. The math works, but the result becomes absurdly large. We look at that case in the section on small numbers.

How should you read percent change with negative values?

Some metrics can go below zero, for example net follower change or net subscriber change. When the base is negative, the standard formula produces results with the wrong sign.

Worked example: last month your net follower change was -50, meaning you lost more followers than you gained. This month it is +30. If you apply the formula as is, (30 - (-50)) / -50 × 100 returns -160%. So the report shows a decline even though things improved.

A common fix is to use the absolute value of the old number in the denominator: 80 / 50 × 100, a 160% improvement. Our percentage calculator also applies this method when the old value is negative. Even so, readers often misread this kind of figure.

That is why we lead with the absolute change when the base is negative: "Net follower change went from -50 to +30 (an improvement of 80 people)." Give the percentage only as supporting detail, and state the method you used.

Why do percent change and percent difference give different answers?

Percent change is directional: there is a before and an after. Percent difference, on the other hand, fits cases where neither value comes first. For example, it suits a comparison of two ad groups or two cities.

A common definition of percent difference divides the absolute gap by the average of the two values. Worked example: ad group A brought 80 conversions and ad group B brought 120. The gap is 40 and the average is 100, so the percent difference is 40%. Yet if you take A as the base, B is 50% higher. If you take B as the base, A is about 33.3% lower.

All three numbers are correct within their own definition. The problem is giving a number without the definition. We recommend sentences that name the base, such as "Group B delivered 50% more conversions than group A." Then readers do not have to guess your reference point.

Why is percentage increase misleading with small numbers?

With small bases, even a one-unit change produces a huge percentage. Worked example: if a product page made 2 sales last week and 5 this week, the percentage increase is 150%. It looks impressive on paper, but the gap could be pure chance.

In our reports, we always pair small-base percentages with the absolute numbers: "from 2 to 5 (+3 sales)." It also helps to leave the percent column blank below a set threshold. Choose that threshold based on your own volume, because no single number fits every business.

The reverse also holds. On a very large base, a 2% increase looks modest, yet it can mean thousands of extra visits. In short, percentages hide scale, and absolute numbers hide proportion. Show both, and the picture is complete.

What do the comparison views in Google Ads and Search Console show?

Platforms calculate percent change for you, but knowing how they do it makes interpretation easier. According to the Google Ads Help guide to comparing date ranges, turning on a comparison adds percent change to the campaign, ad group, and ad tables. When you expand a column, you see the current range, the comparison range, the numerical difference, and the percent change side by side.

In Search Console, comparing two date ranges in the Performance report adds a difference column to the table. The Search Console Help page on advanced filtering and comparison suggests weekly or monthly granularity for date comparisons. That way, the day-of-week effect disappears.

One practical note: the platform's percentage and your manual result may differ slightly. Usually the cause is rounding, or a different date range selected in each view. First align the dates, then calculate with the raw numbers before any rounding. Menu labels change over time, so always confirm the current steps on the official help page.

How should you read changes in conversion rate and ROAS?

Conversion rate is a rate too, so report its change both in points and as a relative percentage. Worked example: if conversion rate fell from 2.5% to 2.0%, that is a drop of 0.5 points, or 20% in relative terms. You can get the rate for each period from our conversion rate calculator and then compare the two with the formula above.

ROAS (return on ad spend) is a ratio, not a percentage, yet you still express its change as a percentage. For example, if ROAS went from 4.0 to 5.0, the increase is 25%. Our ROAS calculator gives you the ratio for one period; you then compare two periods with the formula from this guide.

With rates, also separate where the change came from. Conversion rate can fall while the number of conversions rises, because traffic grew faster. We cover the typical causes of a ROAS decline in our guide on ROAS drop causes and diagnosis.

How should you word percent change in a report?

A correct calculation loses its value if the wording is off. Our team uses a four-part pattern in monthly reports:

• Metric name and period: "October organic clicks versus September".
• Absolute values: "from 4,500 to 5,175".
• Percent change and direction: "a 15% increase".
• For rates, the point change: "CTR from 3.0% to 3.6% (+0.6 points)".

Keep the number of decimal places consistent as well. Writing 15% on one line and 14.87% on the next suggests a precision that is not really there. For most marketing reports, one decimal place is plenty.

If you want to read the whole report with confidence, see our guide on how to read a digital marketing report. We also explain which metrics deserve tracking in our overview of digital marketing KPIs.

What are the most common percentage increase mistakes?

Over the years, we have seen the same mistakes in report after report. Fortunately, each one has a simple fix:

1. Dividing the change by the new value. The base is always the old value.
2. Confusing percentage points with percent change. For rates, write both.
3. Adding consecutive percentages. Multiply the multipliers instead.
4. Giving a percentage on a zero or tiny base. Lead with the absolute number.
5. Comparing periods of different lengths. Switch to daily averages or pick equal periods.
6. Multiplying by 100 twice. Check the cell format.
7. Subtracting a percentage of the new value in a reverse calculation. Divide by the multiplier.

You can use this list as a quick checklist before you send any report. Our guide on how to read an SEO report shows how the same mistakes appear in Search Console data.

Key takeaways on percentage increase and decrease

To sum up, percent change has one formula: (new - old) / old × 100. The base is always the old value, and only the sign separates an increase from a decrease. For rates, you give both the point change and the relative change. You multiply consecutive percentages, and you take averages geometrically.

With zero, negative, or small bases, you lead with the absolute number rather than the percentage. These few rules prevent most interpretation errors in a marketing report. They also help everyone on your team speak the same language.

Reading reports correctly means making budget and content decisions correctly. At Talha Aslan and team, we take this discipline seriously in every reporting process. Next time you prepare a report, start by checking the numbers with the steps in this guide.

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