Percentage calculator
Pick the question you are asking. The working is shown under the answer.
Percentage points are not per cent
If a rate goes from 4% to 6%, that is an increase of two percentage points and an increase of fifty per cent. Both are true and they describe the same change, which is exactly why the difference gets exploited in headlines.
The rule: percentage points when comparing two percentages, per cent when comparing two quantities. This calculator shows both whenever the numbers make it plausible you meant the first.
Adding and removing a percentage do not cancel
Take 20% off 100 and you get 80. Add 20% back and you get 96, not 100.
That is not a rounding artefact - the second percentage is taken from a smaller base. To undo a 20% discount you divide by 0.8, which is a 25% increase. It is the same reason "50% off, then another 50% off" is a 75% discount rather than a free item.
Percentage change from zero
There is no answer. Any increase from nothing is infinite in percentage terms, so the calculator says so rather than printing a number. Quote the absolute change instead: "up from 0 to 40", not "up 4000%".