How to Write Numbers, Dates and Times in English

Numbers, dates, and times feel like they should be universal. A 5 is a 5 in every language. But the way you write them in English follows conventions that rarely match the rules you learned in your first language — and getting them wrong is one of the fastest ways to make otherwise strong writing look unpolished. A date that reads as June to you reads as May to your reader. A decimal comma turns 1,5 into "one thousand five hundred." None of this is about grammar. It is about formatting conventions that English speakers absorb without noticing and that ESL writers have to learn deliberately.

This guide walks through the rules that trip people up most, with concrete wrong-versus-right examples and the US versus UK differences that matter.

Numbers: when to spell them out and when to use digits

The single most common question is whether to write seven or 7. The widely used rule: spell out numbers under ten, use digits for 10 and above.

Wrong: I sent 7 emails and got 3 replies.

Right: I sent seven emails and got three replies.

Wrong: The team reviewed twelve applications.

Right: The team reviewed 12 applications.

Some style guides go further. The Chicago Manual of Style spells out every whole number under 100 ("forty-two attendees"), while news and most business writing use the under-ten cutoff. Either is acceptable. What is not acceptable is switching mid-document — pick one and stay consistent.

There are exceptions that always take digits, no matter how small the number: ages used as labels, percentages, money, measurements with units, and anything in a date or time. So you write "a 5-year-old laptop," "3%," "$4," and "9 a.m." — even though the numbers are under ten.

Never start a sentence with a numeral

This one catches almost everyone. If a number falls at the very start of a sentence, you spell it out — even if you would normally use digits.

Wrong: 25 people attended the launch.

Right: Twenty-five people attended the launch.

If spelling it out feels clumsy (large numbers, especially), rewrite the sentence so the number is not first.

Awkward: One thousand two hundred users signed up.

Better: The launch drew 1,200 sign-ups.

Ordinals, percentages, and large numbers

Ordinals (first, second, third) follow the same spell-out logic in prose: "the third quarter," not "the 3rd quarter." In dates and lists, the numeral form (1st, 2nd, 3rd) is fine. Note the suffixes are not raised or superscripted in standard writing — write "1st," not "1ˢᵗ."

For percentages, digits plus the word or symbol: "5 percent" in formal prose, "5%" in technical or business writing. Do not write "five %."

Large numbers use commas as thousands separators in English: 1,000 — 25,000 — 1,000,000. (More on why the comma matters below.) In running prose, very large round numbers often read better spelled out: "two billion users" rather than "2,000,000,000 users."

Dates: the biggest source of international confusion

Here is where your reader's country changes everything. The same string of digits means two different dates depending on who reads it.

Ambiguous: The contract starts 06/05/2026.

To an American, that is June 5. To almost everyone else, it is 5 June. There is no way to know which you meant. All-numeric dates with slashes are genuinely unsafe for international writing — avoid them whenever a real human will read the date.

US versus UK written dates

The US puts the month first and adds a comma before the year:

US: June 26, 2026

The UK (and most of the world) puts the day first and drops the comma:

UK: 26 June 2026

Both spell out the month, which is exactly why they are safe — nobody can misread "June." Match the convention to your audience: US-facing email gets the US form, a British or international reader gets the day-first form.

ISO 8601: the unambiguous option

When you need a date that cannot be misread by anyone, anywhere — in filenames, spreadsheets, technical documents, or international correspondence — use the ISO 8601 format: year-month-day, always with four-digit year and two-digit month and day.

Unambiguous: 2026-06-26

It sorts correctly, it is language-neutral, and there is only one way to read it. It is too rigid for a friendly email, but for anything that crosses borders or gets sorted by a computer, it is the right call.

Times: a.m./p.m. versus the 24-hour clock

English has two time systems, and which you use depends on register and region. The 12-hour clock with a.m./p.m. is standard in everyday US and UK writing.

Wrong: The call is at 15:00 PM.

Right: The call is at 3:00 p.m.

Note: "15:00 PM" is doubly wrong — 24-hour time never takes a.m./p.m., and the two systems are never mixed. Write either "3:00 p.m." or "15:00," never both.

Formatting details that matter:

• Use a colon between hours and minutes: 9:30, not 9.30 (though British writing sometimes uses 9.30 — see the table).
• For times on the hour, you can drop the minutes: "9 a.m." is fine; "9:00 a.m." is more formal.
• "a.m." and "p.m." are usually lowercase with periods in American style; "am"/"pm" without periods is common in British style.
• Noon and midnight are clearer than "12 p.m." / "12 a.m.," which confuse even native speakers.

The 24-hour clock (sometimes called "military time" in the US) is standard in technical, medical, transport, and international contexts: "Departure at 18:45." In conversational writing, expressions like "half past seven" (7:30) and "quarter to nine" (8:45) are common, especially in British English — but use them only in informal prose, never in a schedule or table.

Decimals and thousands: the comma trap

This is the mistake that changes the actual number, so it matters most. English uses a period for the decimal point and a comma to group thousands. Many languages do the exact opposite.

Wrong (European convention): The total was 1.250,75 euros.

Right (English convention): The total was 1,250.75 euros.

If you write "1,5 hours" in English, your reader sees "one thousand five hundred hours." Always write "1.5 hours." This single swap — comma for thousands, period for decimals — clears up a surprising amount of confusion in financial, scientific, and data writing.

Currency: symbol first, no space

In English, the currency symbol goes before the amount, with no space between them. Many languages put it after.

Wrong: The plan costs 29$ per month.

Right: The plan costs $29 per month.

The same holds for £, €, and ¥: write "£5," "€20," "¥100" — symbol first, number flush against it. For round amounts in prose you can spell it out ("five million dollars"), but in tables, invoices, and pricing, keep the symbol-first numeral form.

Phone numbers and large figures

Phone formatting is regional and you should follow the convention of the country you are writing to. US numbers group as (212) 555-0142 or 212-555-0142; UK numbers group differently, like +44 20 7946 0958. For international audiences, lead with the country code in +XX form. Do not invent your own grouping — copy the local pattern.

For very large numbers in formal writing, mixing words and digits is normal and readable: "$3.2 billion," "1.5 million downloads." This is clearer than a wall of zeros and is standard in journalism and business prose alike.

US vs UK quick reference

Clean up formatting before you send

Most of these slips survive a grammar check because they are not grammar errors — they are formatting conventions. A sentence with "1,5 hours" or "29$" is perfectly grammatical and still wrong. If you want a fast pass over a draft, the free Text Cleaner strips out the stray spacing and punctuation noise that often rides along with copied-in numbers and dates, so what remains is easier to format correctly by hand.

For the deeper passes — catching a date in the wrong regional order or a decimal comma that flips your meaning — the Diglot grammar checker flags the patterns native readers notice instantly but ESL writers miss. And because Diglot is built for bilingual writers, it understands that "1.250,75" is not a typo in your head — it is your first language showing through, and it helps you convert it cleanly into English convention.

Number formatting is one piece of a larger set of conventions that separate confident English writing from the kind that quietly signals "non-native." If this was useful, two sibling guides cover the same territory: the rules of punctuation differences for non-native writers and how to fix sentence fragments and run-ons in English.

The fixes here are small, mechanical, and entirely learnable. Get the conventions right once and they stop being something you think about — they just become the way you write. Pick the audience, match the convention, stay consistent, and let a checker catch the rest. Try the Diglot grammar checker on your next draft and see how many number and date slips it catches that a standard spell-check walks right past.