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$91+ Cheap flights from Philadelphia (PHL) to Boulder, CO

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 3/9. Fares are subject to change and may not be available on all flights or dates of travel.
PHL — DEN
Jan 14 — Jan 211
Wed 1/14
Wed 1/21
1 adult, Economy
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Cheapflights Tip: The best prices from Philadelphia to Boulder are usually found in July or August, booked 40 days in advance, depart on a Friday or Thursday and return on a Thursday

Cheap flight deals from Philadelphia to Boulder

Cheapest flights from Philadelphia to Boulder
Explore the most affordable flight options available from Philadelphia to Boulder. Find the lowest fares from popular airlines and budget airlines, with prices last updated on December 15, 2025.

This CheapOair deal was found by Cheapflights users on 12/14. 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 12/316:00 amPHL - DEN
1 stop17h 49mFrontier
Mon 1/511:59 pmDEN - PHL
1 stop12h 39mFrontier
Deal found 12/14$184
This Kiwi.com deal was found by Cheapflights users on 12/13. 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 12/217:05 amPHL - DEN
1 stop15h 00mFrontier
Mon 12/296:05 amDEN - PHL
1 stop16h 21mFrontier
Deal found 12/13$220
This Kiwi.com deal was found by Cheapflights users on 12/14. 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.
Wed 12/316:00 amPHL - DEN
1 stop17h 49mFrontier
Fri 1/26:25 amDEN - PHL
1 stop9h 38mFrontier
Deal found 12/14$221
This Frontier deal was found by Cheapflights users on 12/13. 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.
Sun 12/217:05 amPHL - DEN
1 stop15h 00mFrontier
Thu 12/256:05 amDEN - PHL
1 stop8h 51mFrontier
Deal found 12/13$232
This Super.com deal was found by Cheapflights users on 12/15. 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 Super.com is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 12/256:30 amPHL - DEN
1 stop9h 45mFrontier
Mon 1/511:59 pmDEN - PHL
1 stop12h 39mFrontier
Deal found 12/15$233
This CheapOair deal was found by Cheapflights users on 12/14. 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.
Tue 12/231:54 pmPHL - DEN
1 stop11h 19mFrontier
Mon 12/296:05 amDEN - PHL
1 stop16h 21mFrontier
Deal found 12/14$234
This Delta deal was found by Cheapflights users on 12/14. 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 Delta is selected, and click “Compare selected” under the list of providers to see comparable flight deals.
Thu 12/256:05 amPHL - DEN
1 stop6h 24mDelta
Wed 12/317:05 amDEN - PHL
1 stop7h 33mDelta
Deal found 12/14$237
This CheapOair deal was found by Cheapflights users on 12/14. 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 12/316:00 amPHL - DEN
1 stop17h 49mFrontier
Sun 1/411:59 pmDEN - PHL
Nonstop3h 32mFrontier
Deal found 12/14$247

Find flight deals from Philadelphia to Boulder

Keep the following information in mind while searching for Philadelphia to Boulder flight deals. Data was last updated December 15, 2025.

Most accurate provider

CheapOair
3 stars

Most trusted provider

CheapOair
3 stars

Round-trip from

$139
(Trip.com)

One-way from

$91
(Expedia)

Popular in

December

Cheapest in

July

Average price

$391
Provider with most accurate pricing for Philadelphia-Denver Intl flight deals.
Search Deals
Provider most trusted by Cheapflights users for Philadelphia-Denver Intl flights.
Search Deals
From Philadelphia to Boulder
Search Deals
One-way flight from Philadelphia to Boulder
Search Deals
Highest demand for flights based on searches. 5% potential increase in price ($19 potential increase over avg. RT price).
Search Deals
Cheapest flight prices on average. 2% potential price decrease ($7 potential savings vs. average RT price).
Search Deals
Average for round-trip flights in December 2025
Search Deals

Cheapflights Fare Finder

 
Customize your flight search to find flights from Philadelphia to Boulder 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 December 15, 2025.
Use the filters below to find and compare flights from Philadelphia to Boulder that are best for you.

Fly from

Philadelphia

Fly to

Boulder

Route

Depart

Return

Price

PhiladelphiaDenver

PHL - DEN

PHLDEN

Philadelphia

Sat 2/7

3:43 pm-6:12 pm

Nonstop4h 29m

Denver Intl

Sat 2/14

6:00 am-2:19 pm

1 stop6h 19m

$233

PhiladelphiaDenver

PHL - DEN

PHLDEN

Philadelphia

Sat 2/14

10:06 am-4:36 pm

1 stop8h 30m

Denver Intl

Sat 2/21

5:50 pm-11:23 pm

Nonstop3h 33m

$233

PhiladelphiaDenver

PHL - DEN

PHLDEN

Philadelphia

Thu 12/25

6:05 am-10:29 am

1 stop6h 24m

Denver Intl

Wed 12/31

7:05 am-4:38 pm

1 stop7h 33m

$237

PhiladelphiaDenver

PHL - DEN

PHLDEN

Philadelphia

Sat 2/21

3:37 pm-6:07 pm

Nonstop4h 30m

Denver Intl

Sat 2/28

5:50 pm-11:23 pm

Nonstop3h 33m

$249

PhiladelphiaDenver

PHL - DEN

PHLDEN

Philadelphia

Tue 1/6

5:00 pm-7:20 pm

Nonstop4h 20m

Denver Intl

Tue 1/13

1:25 pm-8:20 pm

1 stop4h 55m

$259

PhiladelphiaDenver

PHL - DEN

PHLDEN

Philadelphia

Sat 1/24

2:05 pm-4:25 pm

Nonstop4h 20m

Denver Intl

Wed 1/28

9:10 am-5:25 pm

1 stop6h 15m

$259

PhiladelphiaDenver

PHL - DEN

PHLDEN

Philadelphia

Thu 1/1

8:00 am-10:29 am

Nonstop4h 29m

Denver Intl

Tue 1/6

5:55 pm-11:30 pm

Nonstop3h 35m

$303

PhiladelphiaDenver

PHL - DEN

PHLDEN

Philadelphia

Wed 2/18

10:35 am-4:23 pm

1 stop7h 48m

Denver Intl

Sat 2/21

5:50 pm-11:23 pm

Nonstop3h 33m

$313

PhiladelphiaDenver

PHL - DEN

PHLDEN

Philadelphia

Tue 2/10

3:43 pm-6:12 pm

Nonstop4h 29m

Denver Intl

Wed 2/18

6:00 am-2:19 pm

1 stop6h 19m

$313

PhiladelphiaDenver

PHL - DEN

PHLDEN

Philadelphia

Sat 2/28

5:40 pm-8:00 pm

Nonstop4h 20m

Denver Intl

Thu 3/5

11:05 am-4:30 pm

Nonstop3h 25m

$317

Flights are sorted by cheapest round-trip flights first.

Deals found on 12/14

Showing 1-10 of 22 results
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Best time to book a flight from Philadelphia to Boulder

Have a flexible travel schedule? Discover the best time to fly to Boulder from Philadelphia 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 Philadelphia to Boulder

How far ahead should I book a flight from Philadelphia to Boulder?

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

Booking 40 days in advance of your planned departure date is, on average, the best time to get cheap flights from Philadelphia to Boulder. The general trend is that the closer you book to the departure date, the more expensive your flight will be.

What is the cheapest month to book a flight from Philadelphia to Boulder?

Currently, October is the cheapest month in which you can book a flight from Philadelphia to Boulder (average of $88). Flying from Philadelphia to Boulder in May is currently the most expensive (average of $143). 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 PHL to BD9?

Find hourly flight availability from Philadelphia to Boulder. Discover flight options and departure times throughout the day, allowing you to choose a departure time that suits your schedule. Data last updated December 15, 2025.

Unlike in the afternoon, when flights are generally more expensive, you can save up to 25% on flights from Philadelphia to Boulder by exploring options for tickets in the evening.

What is the cheapest day to fly from Philadelphia to Boulder?

Use this chart to determine the cheapest time to fly round-trip from Philadelphia to Boulder. Price data was last updated on December 16, 2024.

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

Weekly flight availability from Philadelphia to Boulder

Explore weekly flight availability from Philadelphia to Boulder. Discover flights operating on different days of the week, giving you the flexibility to choose a travel day that best fits your plans. Compare info to find the most convenient option for your journey. Data last updated December 15, 2025.

The most flights from PHL to BD9 are scheduled on a Friday (14 on average). You will have fewer flight options on Thursday, which is when the least amount of flights are scheduled (4 on average).

How much does it cost to fly round-trip from Philadelphia to Boulder?

Reviews of airlines servicing Boulder

Get insights into the airlines that provide service to Boulder. 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 Boulder. Reviews last updated December 15, 2025.
Read through reviews of airlines operating flights from Philadelphia to Boulder, 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
7.9
Good
4,250 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Overall

7.9

Food

7.0

Entertainment

7.5

Reviews

1 / 20
2.0
Mediocre

Thomas,Dec 2025

SEA - DEN

Plane two hours late in leaving 1:00 pm west coat time got home next day at 2:45am most car rental places are closed and don’t open till 5am
Southwest
7.9
Good
4,250 reviews
Southwest
7.9
Good
4,250 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Overall

7.9

Food

7.0

Entertainment

7.5

Reviews

1 / 20
2.0
Mediocre

Thomas,Dec 2025

SEA - DEN

Plane two hours late in leaving 1:00 pm west coat time got home next day at 2:45am most car rental places are closed and don’t open till 5am
Delta
7.9
Good
8,008 reviews
Southwest
7.9
Good
4,250 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Overall

7.9

Food

7.0

Entertainment

7.5

Reviews

1 / 20
2.0
Mediocre

Thomas,Dec 2025

SEA - DEN

Plane two hours late in leaving 1:00 pm west coat time got home next day at 2:45am most car rental places are closed and don’t open till 5am
United Airlines
7.4
Good
9,092 reviews
Southwest
7.9
Good
4,250 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Overall

7.9

Food

7.0

Entertainment

7.5

Reviews

1 / 20
2.0
Mediocre

Thomas,Dec 2025

SEA - DEN

Plane two hours late in leaving 1:00 pm west coat time got home next day at 2:45am most car rental places are closed and don’t open till 5am
American Airlines
7.2
Good
11,052 reviews
Southwest
7.9
Good
4,250 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Overall

7.9

Food

7.0

Entertainment

7.5

Reviews

1 / 20
2.0
Mediocre

Thomas,Dec 2025

SEA - DEN

Plane two hours late in leaving 1:00 pm west coat time got home next day at 2:45am most car rental places are closed and don’t open till 5am
Frontier
5.8
Fair
3,080 reviews
Southwest
7.9
Good
4,250 reviews

Comfort

8.0

Crew

8.6

Boarding

8.1

Overall

7.9

Food

7.0

Entertainment

7.5

Reviews

1 / 20
2.0
Mediocre

Thomas,Dec 2025

SEA - DEN

Plane two hours late in leaving 1:00 pm west coat time got home next day at 2:45am most car rental places are closed and don’t open till 5am

Related info for your journey

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

  • What airport do you fly from for flights from Philadelphia to Boulder?

    If you book a flight to Boulder from Philadelphia, you will be flying from Philadelphia, which is the city’s only airport. Philadelphia (PHL) is located 7.0 mi from the center of Philadelphia. There are 9 flights from Philadelphia to Boulder per day from 8 different airlines.

  • How popular is this Philadelphia to Boulder flight route?

    This flight path from Philadelphia to Boulder was viewed by 121 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 Philadelphia to Boulder?

    Departing from Philadelphia to Boulder will take you 4h 20m. The distance between Philadelphia and Boulder is about 1553 mi. Both multi-stop and nonstop flights can be found to your destination and back.

  • What are the cheapest airlines to fly from Philadelphia to Boulder one-way?

    For one-way options, check prices for Frontier. According to our data, you can fly for as low as $65. Users have also found prices from $87 and $95 on American Airlines and Southwest, respectively.

  • What are the most reliable airlines from Philadelphia to Boulder?

    The top 3 most reliable airlines when flying from Philadelphia to Boulder are United Airlines (93%), Air Canada (92%) and Frontier (88%).

  • What are the cheapest flights from Philadelphia to Boulder?

    On average you can expect to pay $1,030 for a flight from Philadelphia to Boulder. The cheapest flight overall is $79 while the most popular route, (Philadelphia - Denver Intl) is currently priced at $147.

  • Can I find deals for flights from Philadelphia to Boulder that include hotel bookings?

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

  • How can I find direct flights from Philadelphia to Boulder?

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

  • Can I find deals for business class flights from Philadelphia to Boulder?

    Yes. Cheapflights offers flight deals from Philadelphia to Boulder 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 Philadelphia to Boulder?

    Currently, October is the cheapest month in which you can book a flight from Philadelphia to Boulder (average of $88). Flying from Philadelphia to Boulder in May is currently the most expensive (average of $143). 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

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Alternative routes for Philadelphia to Boulder

See prices for flight routes from nearby airports that may be better suited for you.
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Top 8 airlines flying from Philadelphia to Boulder

Discover the top 8 airlines that operate flights from Philadelphia to Boulder. 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 December 15, 2025.
AirlineCheapestAverageFlexibilityOn-time
Allegiant AirCheapest$106Average$194FlexibilityNo cancel feeOn-time88%
FrontierCheapest$117Average$226FlexibilityNo cancel feeOn-time62%
DeltaCheapest$134Average$434FlexibilityNo cancel feeOn-timeN/A
Sun Country AirCheapest$177Average$275FlexibilityNo cancel feeOn-time83%
United AirlinesCheapest$190Average$485FlexibilityNo cancel feeOn-time69%
SouthwestCheapest$198Average$409FlexibilityNo cancel feeOn-time63%
American AirlinesCheapest$201Average$434FlexibilityNo cancel feeOn-time71%
JetBlueCheapest$207Average$260FlexibilityNo cancel feeOn-time62%

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