Any percentage spelled out, in both spellings — plus the distinction that changes what a number actually claims.
Type a percentage to see it in words, in both spellings.
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01 · the rule
Fifteen percent. The number in words, then the unit — which never takes a plural, however many there are.
A decimal part follows the ordinary English rule and is read digit by digit: 7.5% is "seven point five percent", not "seven point five percents" and not "seven and a half percents". The word behaves like a unit of measure, because that is what it is — per cent, by the hundred.
That is the whole of the grammar. The two things worth more than a sentence are the spelling, which splits by variety, and the percentage point, which is not a spelling question at all.
02 · one word or two
American
fifteen percent
One word, and now the majority form in international and technical writing generally.
British
fifteen per cent
Two words traditionally, from the Latin per centum. Still standard in British publishing.
Neither is wrong, and both are old. The only real error is using them alternately in one document, which reads as carelessness rather than as either convention. The converter above returns both so you can take the one your house style asks for.
03 · worked percentages
| Figure | American | British |
|---|---|---|
| 15% | fifteen percent | fifteen per cent |
| 7.5% | seven point five percent | seven point five per cent |
| 0.5% | zero point five percent | zero point five per cent |
| 100% | one hundred percent | one hundred per cent |
| 250% | two hundred fifty percent | two hundred fifty per cent |
| 33.33% | thirty-three point three three percent | thirty-three point three three per cent |
04 · percentage points
A rate goes from 5% to 7%. Has it risen by two, or by forty? Both — and the sentence has to say which. It rose two percentage points, and it rose forty percent. The two numbers describe the same movement and are not interchangeable.
The gap widens as the base shrinks. A rate moving from 1% to 2% has risen one percentage point — and one hundred percent. Reported as "up 100%" it sounds dramatic; reported as "up one point" it sounds trivial. Neither is a lie, which is precisely the problem.
This is why the phrase "percentage point" exists at all, and why interest rates, unemployment figures and poll results are always reported in points. If you are writing about a change in something that is itself a percentage, the word "points" is not pedantry — it is the only way to be understood.
A useful habit when reading: whenever a percentage change is quoted without a base, assume you have not been told enough, and go looking for the two original numbers.
05 · which form
The same proportion can be written several ways, and each carries a different implication about the size of the sample and the precision of the measurement. Choosing badly is not a grammar error, but it does mislead.
A share out of a hundred invites comparison with other shares and implies the base is reasonably large. Written where the base is tiny, it overstates what is known: "fifty of them" from a sample of four is technically true and thoroughly misleading, and "two out of four" tells the reader what actually happened.
A fraction — two thirds of the members, three quarters of the budget — reads as exact and deliberate, and is the natural form when the denominator is small and meaningful. A ratio — three to one, nine to five — is the right shape when two groups are being weighed against each other rather than one being measured against a whole.
The rule of thumb that survives contact with real writing: if the base is small, name it. If the base is large and the comparison is with other proportions, the share out of a hundred is clearest. And if the reader is meant to weigh two quantities against each other, a ratio says that directly where a share does not.
06 · mistakes
— fifteen percents
+ fifteen percent
Percent is a unit and never takes a plural, the way "per cent of the whole" never did.
— "rates rose 2%" when they went from 5% to 7%
+ rates rose 2 percentage points
Going from 5% to 7% is a rise of two percentage points, but a rise of forty percent. Both numbers are true and they are not the same claim.
— 7.5% as "seven point five percents"
+ seven point five percent
The decimal changes nothing about the unit. The digits after the point are read one at a time, and percent stays singular.
— Mixing "percent" and "per cent" in one document
+ Pick one and keep it
American English writes one word, British English traditionally two. Either is fine; alternating between them in the same text is not.
— 15 % with a space, in American text
+ 15%
American style closes the gap; several European styles and the SI convention keep a thin space. Follow the convention of the language you are writing in.
07 · questions
Q01
The number in words followed by "percent": fifteen percent, one hundred percent. A decimal part is read digit by digit, as everywhere else in English — 7.5% is "seven point five percent". The word percent never takes a plural.
Q02
Both, depending on where you are. American English writes it as one word; British English traditionally writes two, though the single word is now common there too. Neither is an error. What matters is picking one and not alternating within a document.
Q03
The unit for the difference between two percentages. If a rate goes from 5% to 7%, it has risen by two percentage points — and by forty percent. Both are correct and they describe different things, which is why the term exists: without it, "rose 2%" is genuinely ambiguous.
Q04
Because the two numbers can differ enormously. A rate moving from 1% to 2% has gone up one percentage point and one hundred percent. Anyone reporting a change in a rate — interest, unemployment, market share, conversion — has to say which they mean, or the sentence carries no information.
Q05
Figures with the symbol in tables, data and anything technical: 15%. Words in running prose where the number is small or the sentence is formal: fifteen percent. Most style guides also ask you to spell it out at the start of a sentence, where a figure would read oddly.
Q06
Not in American usage: 15%. Several European style guides and the SI convention put a thin space between the number and the sign, which is why you see 15 % in documents translated from French or German. Follow the convention of the language the document is in.
Q07
The same way, and there is nothing wrong with it: two hundred fifty percent means two and a half times. It only becomes a problem when the base is unclear — "sales rose 250%" needs a starting point to mean anything, and readers routinely mistake a 250% rise for a multiplication by 2.5 rather than 3.5.
Q08
Only as many as the underlying data supports. A figure drawn from a sample of two hundred cannot honestly be given to two decimal places; the third digit is noise dressed as precision. Rounding to whole numbers is usually right for survey results, and one decimal place for anything measured rather than counted.
Q09
Yes, in most house styles: "Fifteen percent of respondents agreed", never "15% of respondents agreed". The rule is the general one about not opening a sentence with a figure, and the usual advice is to recast the sentence if the number is long enough to make spelling it out awkward.
Q10
Both put a space before the sign — 15 % — and both use "por ciento" and "por cento" respectively, always as two words. Spanish also takes the definite article in many constructions where English does not: "el 15 % de los votos". Each has its own page here.
And when the thing changing is itself a percentage, say points. The converter above gives both spellings and the decimal fraction alongside.