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$47+ Cheap flights from Ontario to Denver (ONT - DEN)

This is the cheapest one-way flight price found by a Cheapflights user in the last 72 hours by searching for a flight departing on 12/5. Fares are subject to change and may not be available on all flights or dates of travel.
ONT — DEN
Oct 17 — Oct 241
Fri 10/17
Fri 10/24
1 adult, Economy
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Cheapflights Tip: The best prices from Ontario to Denver Intl are usually found in January or February, booked 41 days in advance, depart on a Friday or Thursday and return on a Tuesday

Cheap flight deals from Ontario to Denver

Discover tips and strategies to find the most affordable flight options for your journey from Ontario (ONT) to Denver (DEN). Learn about various techniques such as flexible date searches, comparing prices across and setting up price alerts. Use these methods to find the cheapest flights available for your travel needs. Data last updated September 17, 2025.

Round-trip from

$67
(Cheapflightsfares)

One-way from

$47
(Cheapflightsfares)

Popular in

June

Cheapest in

January

Average price

$157

Good round-trip deal

$168 or less

Good one-way deal

$121 or less
From Ontario to Denver Intl
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One-way flight from Ontario to Denver Intl
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Highest demand for flights based on searches. 17% potential increase in price ($30 potential increase over avg. RT price).
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Cheapest flight prices on average. 4% potential price decrease ($7 potential savings vs. average RT price).
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Average for round-trip flights in September 2025
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Price to beat on a round-trip flight from Ontario to Denver Intl.
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Price to beat on a one-way flight from Ontario to Denver Intl.
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Find flight deals from Ontario to Denver

Cheapest flights from Ontario to Denver
Explore the most affordable flight options available from Ontario to Denver. Find the lowest fares from popular airlines and budget airlines, with prices last updated on September 17, 2025.

This Cheapflightsfares deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 10/117:04 amONT - DEN
Nonstop2h 27mFrontier
Tue 10/1410:29 pmDEN - ONT
Nonstop2h 21mFrontier
Deal found 9/15$67
This Frontier deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 10/147:04 amONT - DEN
Nonstop2h 27mFrontier
Sat 10/1810:29 pmDEN - ONT
Nonstop2h 21mFrontier
Deal found 9/15$68
This Booking.com deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Booking.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Tue 10/147:04 amONT - DEN
Nonstop2h 27mFrontier
Fri 10/178:15 amDEN - ONT
Nonstop2h 20mFrontier
Deal found 9/15$71
This Frontier deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 10/156:53 amONT - DEN
Nonstop2h 25mFrontier
Wed 10/1510:29 pmDEN - ONT
Nonstop2h 21mFrontier
Deal found 9/15$73
This Frontier deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 10/117:04 amONT - DEN
Nonstop2h 27mFrontier
Tue 10/2110:29 pmDEN - ONT
Nonstop2h 21mFrontier
Deal found 9/15$74
This Kiwi.com deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 12/74:02 pmONT - DEN
Nonstop2h 21mFrontier
Thu 12/119:30 amDEN - ONT
Nonstop2h 27mFrontier
Deal found 9/15$75
This Kiwi.com deal was found by Cheapflights users on 9/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Kiwi.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sun 11/96:45 amONT - DEN
Nonstop2h 25mFrontier
Tue 11/188:05 pmDEN - ONT
Nonstop2h 22mFrontier
Deal found 9/17$81
This Cheapflightsfares deal was found by Cheapflights users on 9/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 10/117:04 amONT - DEN
Nonstop2h 27mFrontier
Wed 10/1510:29 pmDEN - ONT
Nonstop2h 21mFrontier
Deal found 9/16$82
This Frontier deal was found by Cheapflights users on 9/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Frontier is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 10/117:04 amONT - DEN
Nonstop2h 27mFrontier
Sat 10/1810:29 pmDEN - ONT
Nonstop2h 21mFrontier
Deal found 9/16$84
This Cheapflightsfares deal was found by Cheapflights users on 9/17. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 11/1312:05 pmONT - DEN
Nonstop2h 29mFrontier
Sun 11/169:48 amDEN - ONT
Nonstop2h 22mFrontier
Deal found 9/17$85
This CheapOair deal was found by Cheapflights users on 9/16. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure CheapOair is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Wed 10/156:53 amONT - DEN
Nonstop2h 25mFrontier
Sun 10/198:15 amDEN - ONT
Nonstop2h 20mFrontier
Deal found 9/16$86
This Cheapflightsfares deal was found by Cheapflights users on 9/15. Clicking the “Pick Dates” button in this card will allow you to select your dates and further customize your flight criteria. From there, click “Find deals”, make sure Cheapflightsfares is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Sat 10/48:59 pmONT - DEN
Nonstop2h 27mFrontier
Tue 10/1410:29 pmDEN - ONT
Nonstop2h 21mFrontier
Deal found 9/15$89

Cheapflights Fare Finder

 
Customize your flight search to find flights from Ontario to Denver that fit within your specific budget. Explore options based on user searches and filter the results based on your desired price range. Find flights that match your budget for a cost-effective journey. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated September 17, 2025.
Use the filters below to find and compare flights from Ontario to Denver that are best for you.

Fly from

Ontario

Fly to

Denver

Route

Depart

Return

Price

OntarioDenver

ONT - DEN

ONTDEN

Ontario

Sat 2/28

6:00 am-4:24 pm

1 stop9h 24m

Denver Intl

Sat 3/7

11:30 am-4:53 pm

1 stop6h 23m

$183

OntarioDenver

ONT - DEN

ONTDEN

Ontario

Tue 12/23

5:05 am-8:24 am

Nonstop2h 19m

Denver Intl

Wed 12/31

7:43 pm-9:07 pm

Nonstop2h 24m

$201

OntarioDenver

ONT - DEN

ONTDEN

Ontario

Sat 12/20

5:05 am-8:24 am

Nonstop2h 19m

Denver Intl

Mon 12/29

11:15 am-12:38 pm

Nonstop2h 23m

$201

OntarioDenver

ONT - DEN

ONTDEN

Ontario

Fri 11/28

5:50 am-9:05 am

Nonstop2h 15m

Denver Intl

Tue 12/2

8:05 am-11:55 am

1 stop4h 50m

$204

OntarioDenver

ONT - DEN

ONTDEN

Ontario

Thu 12/4

8:40 am-3:10 pm

2 stops5h 30m

Denver Intl

Mon 12/8

8:05 am-11:55 am

1 stop4h 50m

$222

OntarioDenver

ONT - DEN

ONTDEN

Ontario

Mon 12/22

6:39 pm-12:26 am

1 stop4h 47m

Denver Intl

Wed 12/31

7:43 pm-9:07 pm

Nonstop2h 24m

$224

OntarioDenver

ONT - DEN

ONTDEN

Ontario

Wed 12/3

1:34 pm-4:47 pm

Nonstop2h 13m

Denver Intl

Wed 12/10

1:25 pm-5:37 pm

1 stop5h 12m

$227

OntarioDenver

ONT - DEN

ONTDEN

Ontario

Thu 10/9

6:36 pm-12:29 am

1 stop4h 53m

Denver Intl

Tue 10/14

1:45 pm-3:02 pm

Nonstop2h 17m

$227

OntarioDenver

ONT - DEN

ONTDEN

Ontario

Tue 11/4

6:40 am-2:10 pm

2 stops6h 30m

Denver Intl

Wed 11/5

8:00 am-1:15 pm

1 stop6h 15m

$232

OntarioDenver

ONT - DEN

ONTDEN

Ontario

Mon 12/22

6:39 pm-12:26 am

1 stop4h 47m

Denver Intl

Thu 1/1

7:43 pm-9:07 pm

Nonstop2h 24m

$237

Flights are sorted by cheapest round-trip flights first.

Deals found on 9/17

Showing 1-10 of 22 results
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The best insider tips for Ontario to Denver flights

Snippets provided in this section are AI-generated based on a summarization of Cheapflights-commissioned articles. The articles are presented as-is, for general informational purposes only, and may not be up-to-date. The opinions contained in the articles are original to the author and reflect their authentic experience, which may vary significantly from the experience of others.
Cheapflights partnered with top experts to bring you the best recommendations for your Ontario to Denver trip
Airlines
Frontier

Frontier's UpFront Plus guarantees an empty middle seat in the front two rows.


Early check-in helps secure your place onboard due to frequent overbooking.

Read more about Frontierby Marisa Garcia
United Airlines

Basic Economy allows a personal item only; no carry-on bags are permitted.


Economy Plus offers extra legroom seats towards the front of the economy cabin.

Read more about United Airlinesby Harriet Baskas
Airports
ONT

ONT offers quick security with smoother lines than LAX, ideal for weekday business travelers. Consider reserving parking to ensure a spot during busy times.

Read more about ONTby Bill Fink
DEN

Take the A Line train from DEN to Union Station for a cost-effective and efficient way to reach downtown Denver in 37 minutes.

Read more about DENby Emily Zemler
Our travel experts
Marisa Garcia

Marisa Garcia

Expert on Frontier

Marisa Garcia

Marisa Garcia

Marisa knows planes inside and out, spending 16 years working on aircraft in hangars at airports around the world. She is an aviation industry expert, specialized in airline interiors and regulations. Ten years ago, she pivoted to journalism. She shares her insights in leading aviation, travel, and business publications and on her site FlightChic.

Read more
Harriet Baskas

Harriet Baskas

Expert on United Airlines

Harriet Baskas

Harriet Baskas

Harriet is an award-winning journalist who is happiest in an airport or an unusual museum. Her stories about airports, air travel, and the business of travel have appeared on NBC News, CNBC, USA TODAY, The Points Guy and other outlets. She is the creator of the StuckatTheAirport.com blog and the author of nine books. When not out on the road or exploring the latest airport amenities, she’s home in Seattle getting ready for the next adventure.

Read more
Bill Fink

Bill Fink

Expert on ONT

Bill Fink

Bill Fink

Bill is an award-winning travel writer with extensive credits covering airlines and the aviation industry for publications including AARP, AFAR, The Points Guy and Yahoo. Based in Portland, Oregon, Bill has traveled to more than 75 countries - and been late for his flight in most of them. He once achieved top-level frequent flier status for all of American, Delta and United Airlines during a single year.

Read more
Emily Zemler

Emily Zemler

Expert on DEN

Emily Zemler

Emily Zemler

Emily is a freelance writer and book author based in London covering entertainment and travel. Her work has appeared in Los Angeles Times, Observer, and Conde Nast Traveler She has ventured to more than 40 countries and all seven continents, always in search of a great art museum. She has written extensively about hotels, luxury travel, and aviation.

Read more

Best time to book a flight from Ontario to Denver

Have a flexible travel schedule? Discover the best time to fly to Denver from Ontario with our price prediction graph.
Estimated round-trip price
Rates are based on past data. Find the cheapest month and day to book your flight based on your travel requirements, then search for cheap deals.

Cheapflights Insights

Everything you need to know about your flight from Ontario to Denver

How far ahead should I book a flight from Ontario to Denver?

Use this chart to determine the optimal time to book a round-trip flight from Ontario to Denver. Price data was last updated on September 12, 2025.

The price you pay for your flight from Ontario to Denver may vary depending on when you book. For the best chance of a lower fare, look to book 41 days in advance of your trip. Fares are likely to increase a fortnight or so before your departure date.

What is the cheapest month to book a flight from Ontario to Denver?

Currently, October is the cheapest month in which you can book a flight from Ontario to Denver (average of $197). Flying from Ontario to Denver in March is currently the most expensive (average of $278). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.

What is the cheapest time of day to fly from ONT to DEN?

Find hourly flight availability from Ontario to Denver. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated September 17, 2025.

It’s typically best to fly out from Ontario to Denver in the evening. Doing so could potentially save you 56% on the flight price compared to flying at noon, which is usually more expensive.

What is the cheapest day to fly from Ontario to Denver?

Use this chart to determine the cheapest time to fly round-trip from Ontario to Denver. Price data was last updated on September 14, 2025.

Travelers seeking maximum savings on their Ontario to Denver flight should consider departing on Tuesday evenings when fares are most often at their lowest. Sunday at noon flights should be avoided if possible as fares are typically the most expensive at this time.

Reviews of airlines servicing Denver

Get insights into the airlines that provide service to Denver. Read reviews, discover amenities, and learn about the overall travel experience offered by airlines. Use this information to make informed decisions when choosing an airline for your flight to Denver. Reviews last updated September 17, 2025.
Read through reviews of airlines operating flights from Ontario to Denver, such as Southwest, Delta, and United Airlines. Reviews also offer insight into each airline's entertainment options, comfort, food, crew/service, and boarding process.
Southwest
8.0
Very good
4,242 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Boarding

8.1

Crew

8.6

Overall

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
Southwest
8.0
Very good
4,242 reviews
Southwest
8.0
Very good
4,242 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Boarding

8.1

Crew

8.6

Overall

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
Delta
8.0
Very good
7,961 reviews
Southwest
8.0
Very good
4,242 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Boarding

8.1

Crew

8.6

Overall

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
United Airlines
7.4
Good
8,926 reviews
Southwest
8.0
Very good
4,242 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Boarding

8.1

Crew

8.6

Overall

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.
Frontier
5.8
Fair
3,173 reviews
Southwest
8.0
Very good
4,242 reviews

Comfort

8.0

Entertainment

7.5

Food

7.0

Boarding

8.1

Crew

8.6

Overall

8.0

Reviews

1 / 20
8.0
Excellent

Walter,Aug 2025

OAK - SAN

Dozens of flights and I've never seen a row's beverages forgotten. I even went back and asked the attendant to check on them and nothing. I really hope it didn't have something to do with the Black mother with her kid in the row. Otherwise it was a typical Southwest flight, rapid boarding, tolerable leg room.

Related info for your journey

Find useful and relevant information for your journey from Ontario to Denver. Access travel guides, tips, and recommendations to enhance your travel experience. Get information about local attractions, weather, transportation options, and more.

  • What airports do I use to fly from Ontario to Denver?

    If you book a flight from Ontario to Denver, you will be flying from Ontario to Denver Intl. Flights to Denver Intl (DEN) from Ontario (ONT) take 2h 11m for a nonstop flight. There are 9 flights from Ontario to Denver per day from 4 airlines.

  • How popular is this Ontario to Denver flight route?

    The Ontario to Denver Intl flight path was viewed by 340 users in the past month. Keep an eye out for changes in search interest prior to high and low season.

  • How long is the flight from Ontario to Denver?

    For as low as $204, Alaska Airlines can have you in Denver from Ontario in 2h 15m. The distance between Ontario and Denver is about 817 mi. When browsing for deals, the options you’ll see will be for both nonstop flights and flights with stops.

  • What are the cheapest airlines flying from Ontario to Denver round-trip?

    Currently priced at $58, Frontier will fly you from Ontario to Denver and back. In addition to Frontier, many other airlines offer competitively priced options for your trip. Search Cheapflights for deals from Southwest and United Airlines - these airlines can fly you to your destination from $121 and $136, respectively. These flights start at 61% lower than the current average price 3 months from now.

  • What are the most reliable airlines from Ontario to Denver?

    The top 3 most reliable airlines when flying from Ontario to Denver are Air Canada (79%), Frontier (74%) and United Airlines (74%).

  • What are the cheapest flights from Ontario to Denver?

    While on average a flight from Ontario to Denver is generally $598, our data shows the cheapest flight currently is $76. When looking at the most popular route, (Ontario - Denver Intl), you can expect to pay $67 for that flight.

  • Can I find deals for flights from Ontario to Denver that include hotel bookings?

    Yes. In addition to deals on Ontario to Denver flights, Cheapflights offers vacation packages that include both flights and hotel.

  • How can I find direct flights from Ontario to Denver?

    After entering your origin and destination, apply the non-stop filter on the search result page to find direct flights from Ontario to Denver.

  • Can I find deals for business class flights from Ontario to Denver?

    Yes. Cheapflights offers flight deals from Ontario to Denver by cabin class. In addition to browsing deals, you can also filter by cabin class on the search results page after making a search.

  • What is the cheapest month to book a flight from Ontario to Denver?

    Currently, October is the cheapest month in which you can book a flight from Ontario to Denver (average of $197). Flying from Ontario to Denver in March is currently the most expensive (average of $278). There are several factors that can impact the price of a flight, so comparing airlines, departure airports and flight times can provide users with more options.

See more FAQs

Traveling to a place near Denver?

Book flights to Denver if you plan to visit one of these locations
Black Hawk
Westminster
Golden
Winter Park
Lakewood
Broomfield
Greeley
Lone Tree
Cripple Creek
Thornton
Silverthorne
Manitou Springs
Fort Morgan
Glendale
Wheat Ridge
Brighton
Longmont
Idaho Springs
Parker
Sterling

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Top 4 airlines flying from Ontario to Denver

Discover the top 4 airlines that operate flights from Ontario to Denver. Compare their services, reliability, and customer satisfaction ratings to choose the airline that best suits your travel preferences and needs. Over the last 7 days, Cheapflights users made 2,558,603 searches. Data last updated September 17, 2025.
AirlineCheapestAverageFlexibilityOn-time
FrontierCheapest$58Average$135FlexibilityNo cancel feeOn-time62%
SouthwestCheapest$121Average$258FlexibilityNo cancel feeOn-time63%
United AirlinesCheapest$136Average$278FlexibilityNo cancel feeOn-time69%
DeltaCheapest$177Average$257FlexibilityNo cancel feeOn-timeN/A

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