A percentage increase describes how much something grew, relative to where it started. Revenue went from $80,000 to $92,000; a rent went from $520 to $575; a page got 1,240 visits last month and 1,600 this month. In each case the raw difference is easy — the useful question is how big that difference is compared to the starting point, because a $12,000 rise means one thing on a base of $80,000 and something entirely different on a base of $2m.
The formula is: subtract the old value from the new value, divide by the old value, then multiply by 100. That denominator is the whole game. The old value is the baseline you are measuring against, and using anything else gives you a different number that answers a different question.
When you need this
Reporting growth. Month-on-month, year-on-year, quarter-on-quarter. Any time you put an arrow next to a figure in a dashboard, this is the calculation behind it.
Understanding a price rise. A supplier moves a unit price from $4.20 to $4.83. That is 15%, and framing it as a percentage tells you far more about whether to push back than the 63-cent difference does.
Comparing changes of different sizes. A team that grew from 4 to 6 people and one that grew from 40 to 50 both added staff, but the first grew 50% and the second 25%. Percentages make growth at different scales comparable.
Worked examples
80,000 to 92,000. The difference is 12,000. Divide by the old value: 12,000 ÷ 80,000 = 0.15. Multiply by 100 for a 15% increase.
520 to 575. The difference is 55. 55 ÷ 520 = 0.1058, so a 10.6% increase.
1,240 to 1,600. The difference is 360. 360 ÷ 1,240 = 0.2903, so a 29% increase.
Doubling. If a figure goes from 50 to 100, the difference is 50, and 50 ÷ 50 = 1, so that is a 100% increase. Doubling is always +100%, tripling is +200%, and a tenfold rise is +900% — the increase is always one less multiple than people expect, because you are measuring the growth, not the result.
Where people go wrong
Dividing by the new value. Using 12,000 ÷ 92,000 gives 13%, not 15%. That figure is not meaningless — it is the decrease you would need to get back from 92,000 to 80,000 — but it is not the increase. Always divide by where you started.
Assuming an increase and a decrease of the same percentage cancel out. They do not. A price that rises 20% and then falls 20% ends up 4% below where it began, because the fall is calculated on a larger base than the rise was. This is one of the most consistently misunderstood things in everyday arithmetic, and we have a whole guide on why percentage rises and falls don’t cancel out.
Adding percentage changes across periods. Three consecutive 10% rises is not a 30% rise; it is 33.1%, because each rise compounds on the one before. To combine successive changes you multiply the factors (1.1 × 1.1 × 1.1 = 1.331), not add the rates.
Confusing “increased by 15%” with “increased to 15%”. The first means the value grew by 15% of itself. The second means it ended up at 15% of some reference figure — usually a catastrophic outcome rather than a good one. One preposition, opposite meanings.
Percentage increases from a base of zero. If something went from 0 to 40, the percentage increase is undefined — you cannot divide by zero, and no percentage can describe growth from nothing. Report the absolute change instead. Software that prints “∞%” or “0%” here is guessing.
Increase, or increase by?
There are two distinct questions and they need different calculators. “Revenue went from 80k to 92k, what percent is that?” is this page. “Revenue is 80k, what is it after a 15% rise?” is the increase by a percentage calculator. Our guide on percentage increase versus increase by a percentage lays out which to reach for.