Calculate percentage change
Measure how much something moved against where it started: going from 80 to 100 is a rise of 20, a 25% increase, labeled as such so the direction is never in doubt. Free in your browser.
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Worked example
- Old value
- 80
- New value
- 100
- Difference
- 20
- Percentage change
- 25
- Direction
- increase
The percentage change calculator compares an original value with a later value and expresses the difference relative to the original. Enter the old value and the new value to receive the absolute difference, percentage change, and a clear increase, decrease, or no-change label. It is useful for prices, revenue, measurements, performance indicators, inventory, and any other quantity tracked over time. The calculation is deterministic, requires no network access, and rejects a zero old value because no finite percentage change can use zero as its baseline.
Choose the correct baseline before calculating
Percentage change always answers a directional question: how much did a new value change relative to an old value? Reversing those fields produces a different result because each calculation uses a different denominator. For example, moving from 80 to 100 is a 25 percent increase, but moving from 100 back to 80 is a 20 percent decrease.
That asymmetry is expected and is one reason percentages should always be reported with their baseline. Use values expressed in the same unit and measured on a comparable basis. Do not compare monthly revenue with annual revenue, kilograms with pounds, or a net figure with a gross figure unless you normalize them first.
Both inputs must be finite numbers. The old value cannot be zero because division by zero does not produce a meaningful finite percentage change. When the baseline is zero, report the absolute change or choose a domain-specific alternative instead of inventing a percentage.
Understand the formula and returned fields
The calculator first subtracts the old value from the new value to obtain the absolute difference. It then divides that difference by the old value and multiplies by 100: percentage change equals ((new value minus old value) divided by old value) times 100. A positive result is labeled an increase, a negative result is labeled a decrease, and zero is labeled no change.
Results are normalized to stable numeric precision, which avoids exposing insignificant floating-point noise while preserving useful accuracy. Negative baselines are accepted and follow the formula literally. In that situation, the sign of the percentage can feel counterintuitive in some business contexts, so interpret it with care and consider whether absolute change is the more informative measure.
The tool does not append a percent sign to the numeric field, making the result straightforward to sort, compare, chart, or pass into another calculation.
Use percentage change responsibly in reports and automation
Percentage change is most useful when it appears beside enough context to explain what moved and over what period. A result such as 12.5 percent is incomplete unless readers know the starting value, ending value, unit, and dates involved. Large percentages often occur when the baseline is small, even if the absolute difference is modest, so consider showing both fields together.
Also distinguish percentage change from percentage-point change. If a conversion rate rises from 20 percent to 25 percent, the increase is 25 percent, while the difference is 5 percentage points. For automated checks, treat the zero-baseline error as a data-quality signal rather than silently replacing zero with another denominator.
Because the capability uses no network, random values, current time, or stored state, identical valid inputs always produce identical outputs, which makes it suitable for repeatable tests, scheduled reporting pipelines, and auditable calculations.
What you can do with it
Track revenue growth
Compare revenue from two equivalent periods and return both the monetary difference and the relative increase or decrease.
Measure a price movement
Quantify how far a product, subscription, or supplier price moved from its previous value.
Monitor operational metrics
Calculate changes in inventory, response time, energy use, defect counts, or other repeated measurements.
FAQ
What does a negative result mean?
For a positive baseline, a negative result indicates a decrease. Negative baselines follow the formula literally and may require domain-specific interpretation.
Is percentage change the same as percentage-point change?
No. A rate moving from 20% to 25% changes by 5 percentage points but increases by 25% relative to its old value.
How do I calculate percentage change between two numbers?
Subtract the old value from the new one, divide by the old value and multiply by 100. From 80 to 100 the difference is 20, and 20 divided by 80 times 100 gives a 25% increase.
Why is 80 to 100 a 25% increase but 100 to 80 only a 20% decrease?
Because each change is measured against its own starting value. A difference of 20 is a quarter of 80 but a fifth of 100, so always report a percentage change together with the value it started from.
Why can't the old value be zero?
The old value is the divisor, and dividing by zero gives no meaningful percentage. When the starting point is zero, report the absolute change instead of inventing a percentage, and the calculator shows a clear input error.
Related tools
For developers — API access
Everything on this page is available programmatically. This section is for teams who want to wire it into their own systems; everyone else can just use the tool above.
API endpoint
Prefer to automate it? One authenticated POST creates the task; the result comes back by webhook or a signed link. The same capability also runs here on the web, by email and from Telegram — and soon from our app too.
Call it from your stack
curl -X POST https://api.kit.forhosting.com/calc2/percentage-change \
-H "Authorization: Bearer $KIT_KEY" \
-H "Content-Type: application/json" \
-d '{"old_value":80,"new_value":100}'const res = await fetch("https://api.kit.forhosting.com/calc2/percentage-change", {
method: "POST",
headers: {
"Authorization": `Bearer ${process.env.KIT_KEY}`,
"Content-Type": "application/json"
},
body: JSON.stringify({
"old_value": 80,
"new_value": 100
})
});
const { task_id } = await res.json();import os, requests
res = requests.post(
"https://api.kit.forhosting.com/calc2/percentage-change",
headers={"Authorization": f"Bearer {os.environ['KIT_KEY']}"},
json={
"old_value": 80,
"new_value": 100
},
)
task_id = res.json()["task_id"]<?php
$res = file_get_contents("https://api.kit.forhosting.com/calc2/percentage-change", false, stream_context_create([
"http" => [
"method" => "POST",
"header" => "Authorization: Bearer " . getenv("KIT_KEY") . "\r\nContent-Type: application/json",
"content" => '{"old_value":80,"new_value":100}',
],
]));
$task = json_decode($res, true);body := bytes.NewBufferString(`{"old_value":80,"new_value":100}`)
req, _ := http.NewRequest("POST", "https://api.kit.forhosting.com/calc2/percentage-change", body)
req.Header.Set("Authorization", "Bearer "+os.Getenv("KIT_KEY"))
req.Header.Set("Content-Type", "application/json")
res, _ := http.DefaultClient.Do(req)Example request
{
"old_value": 80,
"new_value": 100
}Example response
{
"task_id": "tsk_a1b2c3d4e5f6a1b2c3d4e5f6",
"type": "calc2.percentage_change",
"status": "queued",
"_links": {
"result": "/tasks/tsk_…/result"
}
}The API is asynchronous: the call returns a task_id immediately and the result arrives by webhook. Polling is capped at 1 req/s per task.
Pricing
Published price — no tokens, no invented credits. A failed task is never charged.
Errors
| HTTP | Code | Meaning |
|---|---|---|
401 | unauthorized | Missing or invalid API key. |
402 | insufficient_balance | Your balance doesn't cover the task price. |
404 | unknown_type | That task type doesn't exist. |
429 | rate_limited | Too many requests. Use the webhook instead of polling. |
Technical notes
Choose the correct baseline before calculating
The old value is therefore the baseline and belongs in old_value, while the later or comparison value belongs in new_value.
Understand the formula and returned fields
The response includes the two validated inputs, the difference, the percentage_change value, and the direction label so an application does not need to repeat the arithmetic or infer the sign.
Use percentage change responsibly in reports and automation
In dashboards, keep the returned old_value, new_value, and direction with percentage_change so reviewers can verify the claim quickly. API requests cost $0.002 each, and the same deterministic calculation can be used wherever consistent results are needed.
Technical questions
What formula does the calculator use?
It uses ((new_value - old_value) / old_value) × 100.
Why can the old value not be zero?
The old value is the denominator. Dividing by zero cannot produce a finite, meaningful percentage change, so the request returns an invalid_input error.
How much does an API calculation cost?
Each API request costs $0.002.