Percent change,with the sign that matters.
Revenue, price, traffic, conversion rate — the move from one number to the next is the whole story, and +12% or −12% reads very differently in a report. This does percent change, the “X is what % of Y” share, and the “what is X% of Y” amount in one place, and shows the multiplier so you can sanity-check the headline.
Your numbers
Where you started — last month, last year, the old price.
Where you ended up. Negatives are fine.
The verdict
Percent change
25.0%
Difference
25
Multiplier
1.25×
New ÷ original.
Direction
25
Increase.
Original vs new
Sensitivity · same base, different endpoints
How the percentage moves
| New value | Difference | % change | Multiplier |
|---|---|---|---|
| 50.00 | -50.00 | -50.0% | 0.50× |
| 75.00 | -25.00 | -25.0% | 0.75× |
| 90.00 | -10.00 | -10.0% | 0.90× |
| 100.00 | 0.00 | +0.0% | 1.00× |
| 110.00 | 10.00 | +10.0% | 1.10× |
| 125.00 | 25.00 | +25.0% | 1.25× |
| 150.00 | 50.00 | +50.0% | 1.50× |
| 200.00 | 100.00 | +100.0% | 2.00× |
Each row holds your original value of 100.00 fixed and steps the new value by a set percentage. Notice the asymmetry: a −50% and a +50% are not mirror images, because they're measured off the same base but land at very different multipliers.
Your move from 100.00 to 125.00 is a +25.00% change — a 1.25× multiplier.
Your move
The percentage moved. The question is why.
100.00 → 125.00 is a +25.00% change (1.25×).
A number went up or down and you want to know what's actually driving it — pricing, traffic, conversion, churn. Send me the trend behind this figure. In the first 30 minutes I'll tell you whether it's signal or noise and what I'd act on first. Free, and you keep it whether you hire me or not.
Plain English
Percent change is a direction, not just a number.
Percentage change measures how much a number moved relative to where it started. You take the difference between the new value and the old one, divide by the old value, and multiply by 100. A positive result is an increase, a negative result is a decrease — the sign carries half the meaning.
The base is what trips people up. The change is always measured against the original value, not the new one. Going from 100 to 125 is a 25% increase, but coming back down from 125 to 100 is a 20% decrease — same gap of 25, different base, different percentage. That asymmetry is why a 50% drop needs a 100% gain to recover.
This calculator also answers the two questions percent change gets confused with: "X is what percent of Y?" (a share of a whole) and "what is X% of Y?" (a slice of an amount). They use different math, and mixing them up is how a 20% discount turns into the wrong refund. Switch modes and the inputs relabel themselves so you always know which one you're solving.
The formula
% change = (New − Old) ÷ Old × 100
From 100 to 125: (125 − 100) ÷ 100 × 100 = +25%, a 1.25× multiplier. From 125 back to 100: (100 − 125) ÷ 125 × 100 = −20%. Dividing by the original value keeps the percentage in step with the multiplier, including when the base is negative.
Reading the percentage you just got
The original value is 0.
Percent change is undefined — you can't divide by zero, and "infinite percent" is meaningless. Report the absolute change instead ("up 40 signups from a standing start") rather than a percentage.
The number is huge (300%+).
Usually a tiny base, not a real surge. Going from 2 to 8 is +300%, which sounds dramatic for a move of six. Pair big percentages with the raw difference so nobody mistakes noise for a trend.
A drop then a recovery looks even.
It isn't. A −50% fall needs a +100% rise to get back to where you started, because the base shrank. Never net two percentages against each other — convert to multipliers and multiply them.
You crossed zero (negative to positive).
Percent change gets weird and can mislead. When the sign of the base flips, lead with the absolute change; the percentage off a negative base rarely means what a reader assumes.
Using percent change without lying with it
01Always name the base
"Up 25%" is half a fact. Up 25% from what, over what period? The base and the window decide whether the number is impressive or trivial.
02Show the raw difference too
Percentages hide scale. Pair every percent with the absolute change so a +300% from a base of two doesn't read like a +300% from a base of two million.
03Don't add percentages
A +10% then a +10% is +21%, not +20% — the second 10% compounds on the larger base. Multiply the multipliers (1.10 × 1.10) instead of summing the percents.
04Mind the asymmetry
Increases and decreases aren't reversible at the same rate. Plan recoveries off the new, smaller base, not the original one.
05Use percentage points for rates
A conversion rate going 2% → 3% is +1 percentage point, but a +50% relative change. Say which one you mean; reports get wrecked by the difference.
06Pick the right mode
Discounts and tips are "X% of Y". Market share is "X is what % of Y". Period-over-period is percent change. Different questions, different formulas.
07Round late, not early
Round the final percentage, not the inputs. Rounding the base first quietly drifts the answer, especially on small numbers.
08Watch the zero base
Launches, new SKUs, and cold starts have an original value of zero. Report momentum in absolute units until there's a real base to divide by.
The vocabulary
- Percent change
- How much a value moved relative to its original: (new − old) ÷ old × 100. Positive is an increase, negative a decrease.
- Percentage point
- The arithmetic gap between two percentages. 2% to 3% is one percentage point — and a 50% relative increase.
- Multiplier
- The factor the value grew by: new ÷ old. A 25% increase is a 1.25× multiplier; a 50% drop is 0.5×.
- Base value
- The number you divide by — always the original. Changing the base changes the percentage even when the raw difference is identical.
- Absolute change
- The plain difference, new − old, in the original units. Immune to small-base distortion.
- Percentage difference
- Change relative to the average of two values, used when neither is clearly the "before". Distinct from percent change.
Percentage questions, straight answers
Subtract the old value from the new value, divide by the old value, and multiply by 100: (new − old) ÷ old × 100. From 80 to 100 that's (100 − 80) ÷ 80 × 100 = +25%. A positive result is an increase, a negative one a decrease.
Keep going
A calculator tells you what. A call tells you what to do about it.
Send me the account behind these numbers. I'll tell you straight where the money's leaking and what I'd fix first — free, and you keep it whether you hire me or not.