'Time Flies' or 'Time Flys': Which is Correct Grammar?

By Carly Forsaith, updated on September 13, 2022

How do you spell it: 'time flies" or 'time flys"? Which is correct grammar? If you were to perform an online search right now, you might find several sources that list the spelling ‘flys’ as the correct spelling for the plural of ‘fly’. However, this spelling is incorrect.

Today we’re going to dive into the word ‘fly’, explore its several meanings, and understand the reason why it’s spelt the way that it is. 

But before we do that, let us clarify the correct grammar for this sentence. 'Time flies' is the correct way to spell this expression. It is never accurate to spell it 'time flys.'

What Does It Mean?

Do you want to understand the meaning of the word 'fly' and how to use it in a sentence? Great! Stick with us.

‘Fly’ as a Noun

The word ‘fly’ can stand either as a noun or a verb. In the case of a noun, the most commonly understood meaning is that of an insect with wings. For example:

There’s a fly trapped in my bedroom. I’ve opened the window but it can’t seem to find the way out.

There are many other meanings - some more well-known than others - some of which include a vehicle from the 19th century, a pants zipper, or even a hook used in fishing. We won’t go into all the meanings here, as we don't want to drift too far from the focus of the word in the sentence 'time flies'. But feel free to perform an online search if you’re curious; you’ll be surprised how many meanings the word has!

‘Fly’ as a Verb

The word ‘fly’ can also stand in as a verb. The most widely known meaning for the verb is that of moving through the air - usually thanks to wings. For example:

It’s a good thing Superman believed in himself the first time he tried to fly.

In the case of the idiom 'time flies', the word 'fly' is used in its verb form. Read on to know what we mean.

What Does ‘Time Flies’ Mean?

‘Time flies’ is an idiom. An idiom is a term used to refer to a sentence where the meaning isn’t literal. After all, time can’t literally fly, can it? It doesn't have wings. Just like love isn't really blind, as it doesn't have eyes, yet you often hear people say "Love is blind".

So what does it actually mean when someone says ‘time flies’? Quite simply, it’s a way of saying that time goes by quickly. Other ways you could say it include:

  • We were having so much fun, the day flew by really quickly.
  • How time flies! 
  • The day just whizzed by.

How Do You Use ‘Time Flies’ in a Sentence?

To help clarify the meaning of the saying ‘time flies’, let’s see it used in a sentence. We’ll outline a few examples for you below:

Oh wow! I can’t believe it’s already 5 pm. Time flies when you’re having fun!

Your daughter is in college already? My goodness, how time flies.

It also works in the past tense:

Time has flown by since I started working here.

As a quick side note, ‘time flies’ in and of itself is also a sentence. Technically, you don’t have to add anything else to it. Having said that, you usually would want to, in order to clarify the reason why you’re saying that. 

Which One Is Correct - 'Time Flies' or 'Time Flys'?

So when does the word ‘flies’/’flys’ come in, and what is the correct spelling for it? 

As we mentioned earlier, ‘fly’ can be either a verb or a noun. In the case of it being a noun, using that noun in its plural form would warrant the use of an ‘s’ at the end of the word. In the case of it being a verb, conjugating it would sometimes warrant an ‘s’. 

In both cases, the correct spelling is always ‘flies’. ‘Flys’ is never correct.

What Is the Difference between “Flies” and “Flys”?

The difference between ‘flies’ and ‘flys’, and the reason for the confusion between the two is that it is sometimes believed that while the verb form takes on the spelling ‘flies’,  the noun form of the word, when used in its plural form, should be spelt ‘flys’. Again, this is incorrect. It should always be ‘flies’.

An example of the noun in plural form;

We need to take the trash out; it’s attracting flies.

An example of the conjugated verb:

A plane flies up to 45,000 feet high.

When to Use Flys

So where did the spelling ‘flys’ come from, and why do some people believe this to be the correct spelling? 

A ‘fly’ also refers to a horse-drawn carriage, a vehicle commonly used up until the 19th century. The plural of this noun just so happened to be spelled ‘flys’. Whether this was particular to this word, or simply respecting the spelling conventions of the time, the word in this sense is no longer used and as such, neither is the spelling. 

Why Is 'Time Flies' Correct?

We’d now like to get into a bit of grammar. Let’s explore the spelling conventions and conjugation rules that make ‘flies’ the correct spelling in ‘time flies’, and not ‘flys’.

Verbs That End With ‘Y’

In the present tense and third person singular (he/she/it), verbs that end with ‘y’ have specific spelling conventions. If the ‘y’ is preceded by a vowel, then we simply add an ‘s’. For example:

  • Sally always buys the same perfume from the same shop. (Verb: to buy)
  • He plays soccer every Wednesday morning. (Verb: to play)

If the ‘y’ is preceded by a consonant, however, then the ‘y’ is dropped and replaced by ‘ies’. For example:

  • She carries heavy loads daily for her job; it’s not good for her back. (Verb: to carry)
  • Paul tries something new from the menu every time he goes there. (Verb: to try)

Simple enough, right?

It’s worth noting that the past tense also has specific spelling conventions for verbs ending in ‘y’, as do the present and past participles and gerunds, but that will be a grammar lesson for another day. For the purposes of this article, it’s enough to cover just the present tense, since the sentence ‘time flies’ is in the present tense.

Nouns That End With ‘Y’

You’ll be pleased to see that similar rules apply to nouns that end with ‘y’ as they do to verbs that end with ‘y’. Basically, if a vowel precedes the ‘y’, the ‘y’ stays and you just add an ‘s’ to make it plural. For example:

  • I’ve been waiting three days to hear back from them. (Noun: day)
  • Grab the keys, we have to go! (Noun: key)

However, if the ‘y’ is preceded by a consonant, remove the ‘y’ and add ‘ies’ to make the noun plural. For example:

  • December is going to be a busy month - so many parties to attend. (Noun: party)
  • I’ll need five copies of that document, please. (Noun: copy)

As you can see the rule is the same and applies to both nouns and verbs, making it easy enough to remember. 

We hope this is all making more sense now. But just in case we lost you somewhere along the way, let us just summarize. ‘Time flies’ is an idiom, and ‘flies’ is always spelled ‘flies’, and never ‘flys’. To say that time flies is to state the fact that time goes by quickly. 

There, does that help?

Your turn now: tell us, when does time fly for you? Is there an activity that, when you’re doing, you just don’t notice the time? Or perhaps it’s a person? 

Do you know what it is for us? You guessed it! It’s writing about grammar.

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Written By:
Carly Forsaith
Carly Forsaith is one of the lead freelance writers for WritingTips.org. Carly is a copywriter who has been writing about the English language for over 3 years. Before that, she was a teacher in Thailand, helping people learn English as a second language. She is a total grammar nerd and spends her time spotting language errors on signs and on the internet.

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