Why do so many people find it difficult to remember the rules for using numbers in formal writing? Probably because the rules seem a little fuzzy sometimes.

So what can you do? It’s no mystery: as with anything, read and study the rules several times, and it will all seem natural, eventually.

Writing Numbers One through Ten

Spell out numbers one through ten, as in this example:

• My little brother ate four apples before dinner and became ill.
• Why do parents always check to see if babies have ten toes?

Writing Numbers Above Ten

Spell out numbers above ten, unless writing the number would involve using more than two words. For example:

• I have sixty-three dead bugs in my collection.
• My cousin has 207 bugs in his.
• This site has given me a thousand helpful hints for my homework.
• My grandmother is seventy-two today.
• My little sister had about 4,763 measles on her face.

Always Spell Out Numbers that Begin Sentences

It would look odd to begin a sentence with a numeral.

• Four hundred fifty people attended the birthday party.

However, you should try to avoid using long, clunky numbers at the beginning of a sentence. Instead of writing that four hundred and fifty people attended a party, you could re-write:

• There were 450 people at the party.

Dates, Phone Numbers, and Time

Use numbers for dates:

• My birthday is on March 16.
• He was born on Valentines Day, 1975.

And use numbers for phone numbers:

• The phone number for the school is 800-555-6262
• The international code for England is 44.

And use numbers for telling time if using a.m. or p.m.:

• The alarm will sound at 7 p.m.
• I make my bed at 7 a.m. each morning.

But spell out times when using “o’clock” or when the a.m. or p.m. are omitted:

• The alarm will sound at seven o’clock.
• I make my bed at seven each morning.