“Time flies” is correct. “Time flys” is a spelling mistake a very common one, since the eye wants to just tack an -s onto fly the same way we do with most verbs. But fly follows a different rule, and once you see it, you won’t misspell time flies again.
Why I Found It’s “Time Flies”
When I first started digging into this, I expected a complicated explanation. It’s actually simple: “time flies” is the third-person singular present tense of the verb “to fly.” Time is treated as a singular subject, so the verb takes the -s form and for “fly,” that -s form is “flies,” not “flys.”
Compare it to a sentence like “the bird flies south for the winter.” Nobody writes “the bird flys.” The same rule applies here, even though “time flies” is idiomatic rather than literal.
The Grammar Rule I Discovered
English has a spelling rule for verbs (and nouns) ending in a consonant + y: drop the y and add -ies. “Fly” ends in l + y, a consonant followed by y, so it becomes “flies” never “flys.”
The Consonant + Y Rule I Learned
Here’s the pattern spelled out plainly:
● If a verb ends in a consonant + y, change the y to i and add -es.
● fly → flies
● try → tries
● cry → cries
● carry → carries
This isn’t unique to “fly.” It’s a standard English spelling convention that applies to dozens of common verbs, which is exactly why “time flies” trips people up less once they see the wider pattern.
Important Exception I Found
The rule flips when the letter before the y is a vowel instead of a consonant. In that case, you simply add -s and the y stays put: “play” becomes “plays,” “stay” becomes “stays,” and “enjoy” becomes “enjoys.” “Fly” doesn’t qualify for this exception because the letter before the y is “l,” a consonant.
What “Time Flies” Means
Beyond the spelling, “time flies” is an idiom it means time seems to pass unusually quickly. Here’s how it’s typically used.
1. Expressing Surprise
“I can’t believe it’s already December time flies!”
2. Reflecting on Memories
“Looking back at these old photos, time really flies.”
3. “Time Flies When You’re Having Fun”
This is the most common extended version of the phrase used when an enjoyable activity made the hours feel short.
4. “Time Flies By”
Adding “by” is common in casual speech (“time flies by so fast”), and it’s grammatically fine but the core spelling question stays the same: it’s still flies, not flys.
Common Mistakes I’ve Found and How to Avoid Them
Mistake: Writing “time flys” because it looks like it just needs an -s, the way most verbs do.
Why it happens: Most English verbs form the third-person singular by adding -s (“runs,” “jumps,” “talks”), so the brain defaults to that pattern and skips the y-to-ies rule.
Correct: Time flies when you’re on vacation.
Incorrect: Time flys when you’re on vacation.
A second mistake is confusing this phrase with plural nouns like “the flies in the kitchen” and second-guessing the spelling but the verb form and the plural noun form of “fly” happen to be spelled identically, so if you can remember one, you know the other.
Read More: I Analyzed Shiney vs Shiny: Here’s What I Found
Real-World Examples I’ve Collected
Example 1: Social Media Post
“5 years on this app today?? Time flies 🕐”
Example 2: Birthday Card
“Happy birthday! Time flies, but the memories we’ve made together never fade.”
Example 3: Work Email
“I can’t believe it’s already Q4 time flies when the team is this busy. Great work this quarter.”
Example 4: Conversation
“Wait, your daughter is starting college? Wow, time flies.”
Time Flies vs Time Flys: My Summary Table
| Form | Correct? | Why |
| Time flies | ✅ Correct | Follows the consonant + y → ies rule |
| Time flys | ❌ Incorrect | Misapplies the standard -s rule to a consonant + y verb |
| Time flyes | ❌ Incorrect | Adds -es without dropping the y first |
| Time fly | ❌ Incorrect | Missing the required third-person singular verb form |
Other Common Variations I Found
People also search for and sometimes misspell related phrasing, including “time flies fast,” “how time flies,” “time really flies,” and “time sure flies.” In every one of these, “flies” is the correct spelling the surrounding words don’t change the verb form.
Key Pattern I Noticed
Whenever “fly” refers to time, a bird, an insect, or anything else acting as a singular subject in the present tense, the correct spelling is always “flies.” “Flys” only appears as a plural noun in a handful of specialized contexts, like the name of a fishing lure brand or a proper noun never as the verb form used in “time flies.”
Read More: Goodmorning or Good Morning: Which One Is Correct?
Memory Tips I Use to Remember the Rule
Memory Trick #1: The “Baby” Method
“Baby” also ends in consonant + y, and its plural is “babies,” not “babys.” If “babies” looks obviously right to you, apply the same logic to “flies.”
Memory Trick #2: The French Fry Test
“Fry” follows the identical rule: one fry, many fries never “frys.” If you can picture a menu that says “french fries,” you already know the pattern for “flies.”
Memory Trick #3: The Real Flies
Picture actual insects buzzing around a picnic. Nobody writes “there are flys at the picnic” it’s always “flies.” Time flies the same way those insects do: with an -ies ending.
Other Words That Follow the Same Rule
Once you know this pattern, it applies far beyond “fly”:
● study → studies
● carry → carries
● worry → worries
● try → tries
● reply → replies
● spy → spies
● supply → supplies
● deny → denies
● hurry → hurries
● cry → cries
Pro Tip I Learned
If you’re ever unsure whether a verb takes -s or -ies, check the letter right before the final y. Consonant before y means change to -ies; vowel before y means just add -s. This one check resolves almost every case.
Frequently Asked Questions
Is it “time flies” or “time flys”?
“Time flies” is correct. “Time flys” is a common misspelling.
Why isn’t it “time flys” if most verbs just add -s?
Because “fly” ends in a consonant + y. English spelling rules require changing the y to i and adding -es in that case, giving “flies.”
Is “flys” ever correct?
Not as the verb form used in “time flies.” “Flys” only shows up in specific proper nouns or brand names, not in standard grammar.
What does “time flies” mean?
It’s an idiom meaning time seems to pass more quickly than expected, often said when looking back on how fast a period went.
Is “time flies when you’re having fun” grammatically correct?
Yes. It’s a complete, correctly formed sentence and one of the most common uses of the phrase.
What other words follow the same spelling rule as “flies”?
Any verb ending in consonant + y, such as “try” (tries), “carry” (carries), “cry” (cries), and “study” (studies).
David is the creator and author behind Healthy Leeks, a platform focused on grammar, writing skills, and English language learning. Passionate about clear communication and effective writing, David shares practical grammar tips, easy-to-follow language guides, and educational content to help readers improve their English with confidence.
