How is percentage change calculated?

((new − original) ÷ |original|) × 100. From 80 to 100: (20 ÷ 80) × 100 = 25% increase.

What if the original value is zero?

Percentage change from zero is undefined because you cannot divide by zero.

What if the starting value is zero?

Percent change divides by the start. From zero the usual percent is undefined. Report the absolute change (“15 more”) instead of forcing a percent.

How is this different from percent of?

Percent-of multiplies a rate by one number. Change divides the gap between two numbers by the first. You use change when you do not yet know the rate.

What if the new value is zero?

From 40 to 0 is a 100% decrease. That one is defined, because you divided by 40, not by zero. From 0 to 40 is the case that breaks. Say “40 more” instead of a percent.

Should I use the absolute value if the start is negative?

The formula already divides by the absolute value of the start so a negative base does not flip the meaning of the sign twice. Negative bases are rare in prices and common in accounting deltas. If both numbers are profits and one crosses zero, say that in words. A percent across a sign change is easy to quote and hard to interpret.

How do I check a claimed “up 15%”?

You need both endpoints, or one endpoint and a willingness to apply the rate. If they gave you 80 and “up 15%,” the increase calculator should land on 92. If they gave you 80 and 92, this page should say 15%. If they gave you only “up 15%,” there is nothing to check.

Percentage Change Calculator

Measure how much a value grew or shrank from A to B. Positive results are increases; negative results are decreases.

Written and maintained by Ricardo Rodrigues · Last updated October 7, 2026 · What changed

Who this calculator is for

This page starts from two measurements of the same thing. A price last month and a price now, a weight before and after, a bill this year and last year, a score on the same scale. You do not know the rate yet. The rate is the output. Put the reference measurement in From, even when it is the larger one. The sign of the result is the direction.

It is not a comparison of two unrelated piles. “Rent is what percent of salary” is a ratio, the reverse-percent page. “Rent went from 900 to 990” is a change, and it belongs here. The noun has to be the same noun.

Percentage Change

Calculate the percent change from A to B

From (original value)

To (new value)

Result

Enter values to calculate

Comparison table

Direction matters: A → B vs B → A
From	To	Percent change
80	100	25%
100	80	-20%
50	75	50%
75	50	-33.33%
200	50	-75%

The base is always the starting value, so swapping the order changes the answer. For percent difference with no natural starting point, see the percent error guide.

About this percentage change

Percentage change starts with two measurements of the same thing and reports the gap as a percent of the first one. From 80 to 100 is a 25% increase. From 100 to 80 is a 20% decrease. The gap in units is 20 either way; the percent changes because you refused to divide by the same base.

Put the earlier measurement, or the reference measurement, in the starting slot even when it is the larger one. The sign of the result is the direction. A negative percent is a decrease, not an error.

How to use each field

From (original value): The base. Usually the earlier measurement, or the budget, or the figure someone is treating as normal. The gap is divided by the absolute value of this number. Zero cannot be a base; percent change from zero is undefined.
To (new value): The later measurement, or the actual against the reference. It can be larger or smaller. From 50 to 40 is a decrease. You do not flip the boxes to force a positive number. A negative result is the decrease.
The result: A percent with a direction, plus the absolute gap. From 80 to 100 is a 25% increase and a gap of 20. From 100 to 80 is a 20% decrease and a gap of 20. Quote both the percent and the direction. A bare 20 is the gap, not the percent.
No percent button: There is no quick-select on this tab because you are solving for the percent. If you already know the percent, use Increase or Decrease.

When to use this calculator

You have a before and an after: a price, a weight, a headcount, a bill, a score on the same scale.
You want to check that a quoted “up 15%” actually matches the two numbers in the email.
You are comparing the overall move with the story told by two legs (up, then down) that do not add.

Worked examples

Example calculations for Percentage Change
Question	Answer
From 80 to 100	25% increase
From 50 to 40	20% decrease
From 200 to 250	25% increase

Walkthroughs

A grocery staple, one year apart

Olive oil was €7.40 a bottle and is now €8.51. From 7.40 to 8.51. The gap is 1.11. Divide by 7.40: 0.15, exactly 15% increase if the cents are exact. If the new price is 8.50, the change is (1.10 ÷ 7.40) × 100 ≈ 14.86%. Round only when you report it, and say you rounded. The shelf does not owe you a clean percent.

The reverse trip, from 8.51 back to 7.40, is not a 15% decrease. 8.51 × 0.85 = 7.2335, which is short of the old price. The decrease that actually returns to 7.40 is 1.11 / 8.51 ≈ 13.04%. Anyone comparing “it rose 15% and later fell 15%” needs this paragraph.

A KPI that fell, and a boss who wants it positive

Support tickets went from 1,240 to 1,054. From 1240, to 1054. The change is a decrease of about 15%: the gap is 186, and 186 / 1,240 = 0.15. Reporting “+15% improvement” smuggles in a judgment. The calculator’s job is the signed change in the count. Whether fewer tickets is good depends on why they fell. Do not make the From box the smaller number just to get a plus sign. That plus sign would describe a different history.

Formula

Goal	Formula
% change A → B	((B − A) ÷ \|A\|) × 100

Percent change = ((to − from) ÷ |from|) × 100. The absolute value on the base keeps the sign in the numerator, where the direction lives. From 80 to 100: (20 ÷ 80) × 100 = 25. From 100 to 80: (−20 ÷ 100) × 100 = −20. Same gap, different bases, different percents. That asymmetry is the whole subject, not a quirk.

Percentage points are a subtraction. A rate that moves from 2% to 3% is +1 percentage point. The relative change in the rate is (3 − 2) / 2 = 50%. This calculator, given 2 and 3, reports 50%, because 2 and 3 are the numbers you typed. It does not know they were already percents. If you meant points, subtract. Say which one you meant in the sentence.

Two legs do not add. Up 25% and then down 20% can land exactly where you started: 80 to 100 is +25%, 100 to 80 is −20%. The story “up 25 and down 20, so we are ahead by 5” is false. Run the overall change from the first number to the last number. The middle percents are a narrative. The endpoints are the result.

Mistakes this page will not catch for you

Dividing by the new value

The change from 80 to 100 divides 20 by 80. Dividing by 100 yields 20%, which is the decrease in the reverse direction, not the increase you experienced. The formula is attached to the start.

Feeding it two rates that are already percents

From 8 (%) to 10 (%) the tool will say 25%, the relative change in the rate. The percentage-point gap is 2, and this tool does not output points. If you meant points, subtract. Do not paste the 25% into a sentence about the price.

Mixing a partial period into a full one

March versus “the first half of April” is not a percent change in monthly demand. The formula will still divide. The sentence will be wrong because the two numbers do not cover the same kind of interval. Match the windows before you trust the percent.

FAQ

How is percentage change calculated?: ((new − original) ÷ |original|) × 100. From 80 to 100: (20 ÷ 80) × 100 = 25% increase.
What if the original value is zero?: Percentage change from zero is undefined because you cannot divide by zero.
What if the starting value is zero?: Percent change divides by the start. From zero the usual percent is undefined. Report the absolute change (“15 more”) instead of forcing a percent.
How is this different from percent of?: Percent-of multiplies a rate by one number. Change divides the gap between two numbers by the first. You use change when you do not yet know the rate.
What if the new value is zero?: From 40 to 0 is a 100% decrease. That one is defined, because you divided by 40, not by zero. From 0 to 40 is the case that breaks. Say “40 more” instead of a percent.
Should I use the absolute value if the start is negative?: The formula already divides by the absolute value of the start so a negative base does not flip the meaning of the sign twice. Negative bases are rare in prices and common in accounting deltas. If both numbers are profits and one crosses zero, say that in words. A percent across a sign change is easy to quote and hard to interpret.
How do I check a claimed “up 15%”?: You need both endpoints, or one endpoint and a willingness to apply the rate. If they gave you 80 and “up 15%,” the increase calculator should land on 92. If they gave you 80 and 92, this page should say 15%. If they gave you only “up 15%,” there is nothing to check.