Subtract the old value from the new one, divide by the old value, then multiply by 100. Going from 80 to 120 is a 50% increase; going from 120 to 80 is a 33.3% decrease. The same absolute change is a larger percentage from a smaller starting point, so always report the base value alongside it.
What a percentage increase actually tells you
A percentage increase measures how much a number has grown relative to where it started, expressed as a share of the original value rather than a raw count. That “relative to where it started” part is the whole point. Going from 10 sales to 20 and going from 1,000 sales to 1,010 are both a gain of 10 in absolute terms, but the first is a 100% increase and the second is a 1% increase. The percentage tells you which change actually matters.
For anyone running a business, that context is everything. Revenue, leads, conversion rate, ad spend, average order value, organic traffic, almost every metric worth watching is judged not by its size but by its rate of change. Percentage increase (and its mirror, percentage decrease) is the common language growth marketers, founders, and analysts use to compare performance across very different numbers and time frames on equal footing.
The percentage change formula
The math is simple, and it’s worth knowing by hand so the result always makes sense:
Percentage change = ((New value − Original value) ÷ |Original value|) × 100
Step by step, that’s:
- Subtract the original value from the new value. The result is the difference between the two.
- Divide the difference by the original value. Use its absolute value, so a negative starting point still works.
- Multiply by 100. That turns the ratio into a percentage.
A positive answer is an increase; a negative answer is a decrease. Example: a campaign that lifts monthly leads from 80 to 120 is ((120 − 80) ÷ 80) × 100 = +50%. Drop from 120 back to 80 and it’s ((80 − 120) ÷ 120) × 100 = −33.3%, note the percentages aren’t symmetric, because the base you’re dividing by changed. The calculator above handles all of this instantly, but the formula is what keeps you honest about the result.
Percentage decrease: the same formula, read the sign
There is no separate percentage decrease formula. Run the same calculation and a negative answer is the decrease: a price that drops from $250 to $200 is ((200 − 250) ÷ 250) × 100 = −20%, a 20% decrease. That is why this page works as a percentage decrease calculator and a percent change calculator too. Leave the “% change” mode on, enter the higher number first, and the result comes back red with a minus sign.
Percentage increase examples
Each row below is a calculation people searched for before landing here, worked through with the formula above.
| From | To | Difference ÷ original | % change |
|---|---|---|---|
| 80 | 120 | 40 ÷ 80 | +50% |
| 85 | 100 | 15 ÷ 85 | +17.65% |
| 304 | 340 | 36 ÷ 304 | +11.84% |
| 75,000 | 85,000 | 10,000 ÷ 75,000 | +13.33% |
| 140,000 | 150,000 | 10,000 ÷ 140,000 | +7.14% |
| 2.4 million | 3 million | 0.6M ÷ 2.4M | +25% |
| 120 | 80 | −40 ÷ 120 | −33.33% |
Note how adding 10,000 is a 13.33% increase on 75,000 but only 7.14% on 140,000. The same raw gain shrinks as a percentage as the starting number grows.
How to increase or decrease a number by a percentage
Sometimes you know the percentage and need the new number: a price increase, a salary increase, a rent increase or a discount. Convert the percentage to a decimal and multiply:
Increase: New value = Original × (1 + percentage ÷ 100)
Decrease: New value = Original × (1 − percentage ÷ 100)
- Salary increase. A 2.8% raise on $60,000 is 60,000 × 1.028 = $61,680, or $1,680 more a year.
- Rent increase. A 2.5% increase on $2,000 a month is 2,000 × 1.025 = $2,050.
- Price increase. Raising an $85 product by 12% gives 85 × 1.12 = $95.20.
- Discount. 15% off $1,000 is 1,000 × 0.85 = $850.
Use the “Increase by %” or “Decrease by %” mode in the calculator to do this without the decimal conversion.
Finding the original value before a percentage change
The reverse question trips people up most. If this year’s sales of $648,000 are 8% higher than last year, last year was not $648,000 minus 8%. The 8% was calculated on last year’s smaller number, so you divide instead:
Original value = New value ÷ (1 + percentage ÷ 100)
That gives 648,000 ÷ 1.08 = $600,000. Subtracting 8% would have said $596,160, which is $3,840 off. The same works for discounts: an item that costs $85 after 15% off was 85 ÷ 0.85 = $100 before the sale. The “Find original” mode does this for you; enter a negative percentage for a decrease.
Percent vs percentage points
When the numbers you are comparing are already percentages, there are two honest ways to describe the change, and they give very different figures. A conversion rate that moves from 2% to 3% is up 1 percentage point, which is a 50% increase. Both are true; the first is the gap, the second is the relative change.
This is also the answer to “how do you increase a percentage by a percentage?” Increasing a 20% margin by 10% gives 22% (20 × 1.10), while increasing it by 10 percentage points gives 30%. In reports, write “points” for the gap and “%” for the relative change so nobody reads a 50% lift as a 50-point one.
Yearly growth, stacked increases and CAGR
Percentage changes do not add up. Two 10% increases in a row are a 21% total increase (1.10 × 1.10 = 1.21), and a 50% rise followed by a 50% fall leaves you 25% below where you started. To compare growth over several years, use the compound annual growth rate:
CAGR = (End value ÷ Start value)^(1 ÷ years) − 1
Revenue that grows from $100,000 to $150,000 over three years is a 50% total increase but a 14.47% yearly growth rate, not the 16.67% you get by dividing 50 by 3. For a single year-over-year or month-over-month figure, the plain percentage change above is the right tool.
Percentage change vs percentage difference
Percentage change has a direction: an original value and a new one. Percentage difference compares two values with no “before”, such as two stores’ sales in the same month, so it divides by their average instead:
Percentage difference = |A − B| ÷ ((A + B) ÷ 2) × 100
For 80 and 120 that is 40 ÷ 100 = 40%, while the percentage change from 80 to 120 is 50%. If one number clearly came first, use percentage change.
Percentage increase formula in Excel and Google Sheets
With the original value in A2 and the new value in B2, both Excel and Google Sheets use the same formula. Format the result cell as a percentage so 0.5 shows as 50%.
% change: =(B2-A2)/ABS(A2)
Increase A2 by B2%: =A2*(1+B2)
Original before a B2% increase: =A2/(1+B2)
The ABS() keeps the sign right when the original value is negative, such as a loss turning into a smaller loss.
How growth marketers use percentage change
At Growth Boss this calculation runs quietly under almost everything we report to clients. A few of the places percentage change earns its keep:
- Return on ad spend (ROAS) & efficiency. Tracking how much revenue per dollar moves month over month tells you whether paid media is compounding or quietly leaking budget.
- Conversion rate optimization. A landing page that goes from a 2.1% to a 2.8% conversion rate is a 33% lift, a number that justifies the next round of testing far better than “up 0.7 points” does.
- Month-over-month and year-over-year growth. MoM and YoY growth rates are just percentage change applied across time, and they’re the backbone of any honest performance review or growth forecast.
- Cost per acquisition (CAC) & lead volume. Watching CAC fall and qualified-lead volume rise in percentage terms is how you prove a channel is scaling profitably, not just spending more.
- SEO & organic traffic. Sessions, rankings, and revenue from search are all reported as percentage change so a small site and a large one can be measured by the same yardstick.
Reading the result: the base-value trap
The single most common mistake with percentage change is forgetting which number sits in the denominator. Because you divide by the original value, the same absolute swing produces different percentages depending on where you started, which is why a 50% increase followed by a 50% decrease never lands you back where you began. When you compare two percentages, make sure they share the same base and the same time window, or you’re comparing apples to oranges.
Watch out for tiny baselines, too. Going from 2 conversions to 6 is a 200% increase, which sounds spectacular until you remember it’s four extra conversions. Percentages on small numbers are volatile and easy to over-read, pair them with the absolute figures (the difference is shown alongside the result above) so a headline number never hides a small sample. And remember that percentage change only works when the original value isn’t zero; from a true zero baseline there’s nothing to grow from, so report the absolute change instead.
Percentage increase best practices
- Keep the basis consistent. Compare like with like, same metric, same definition, same date range, every time you calculate growth.
- Always show context. A percentage next to its absolute values and its time frame is information; a percentage on its own is a vanity number.
- Round sensibly. Two decimal places is plenty for most marketing reporting; more just implies false precision.
- Sanity-check the direction. Before you act on a number, confirm the increase/decrease label matches what you expected, it’s the fastest way to catch a transposed original and new value.
Where this fits in a real growth system
Measuring growth is the easy part, driving it is the work. A calculator tells you a metric moved; a growth system tells you why, and makes it move again on purpose. That’s what we build for businesses across Oakville, Toronto, and the wider GTA: brand, website and SEO, paid media, and AI automation run as one engine, with the numbers tracked honestly so every decision is backed by real data instead of a hunch.
Measuring a campaign rather than a single number? Try our free ROI calculator, ROAS calculator or conversion rate calculator.