$137 Find Cheap Flights from Philadelphia to Boulder - Compare and Save

This is the cheapest one-way flight price found by a KAYAK user in the last 72 hours by searching for a flight from Philadelphia to Boulder departing on 7/2. Fares are subject to change and may not be available on all flights or dates of travel. Click the price to replicate the search for this deal.
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Everything you should know

Cheapest round-trip
$237
Typical prices: $243-$443
Frontier
Sat 7/25Tue 7/28
PHL - DEN • 1 stop
Cheapest non-stop
$245
Typical prices: $227-$427
Frontier
Tue 8/4Tue 8/11
PHL - DEN • Non-stop
Arrival airport
You can't fly directly to Boulder. It is served by Denver (DEN), located 33.4 miles from Boulder.
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Flight Deals
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Flight Deals

Cheap Flights from Philadelphia to Boulder (PHL-DEN)

 
Here are some of the best deals found on KAYAK recently from the most popular airlines for round-trip flights from Philadelphia to Boulder that are departing in the next months. While these flights were available on KAYAK in the last 72 hours, prices and availability are subject to change and deals may expire.
Discover the best prices for you by selecting your travel dates on KAYAK.

Recent round-trip flight deals from Philadelphia to Boulder

Sat, Jul 25 - Tue, Jul 28
Frontier Logo
1:32 pm - 10:28 pm
PHL
-
DEN
10h 56m
1 stop
Frontier Logo
11:46 pm - 12:22 pm
DEN
-
PHL
10h 36m
1 stop
$237Frontier
Sat, Jul 25 - Tue, Jul 28
Frontier Logo
12:44 pm - 2:58 pm
PHL
-
DEN
4h 14mnonstop
Frontier Logo
6:30 am - 10:28 pm
DEN
-
PHL
13h 58m
1 stop
$238Frontier
Tue, Aug 4 - Wed, Aug 12
Frontier Logo
6:30 am - 2:00 pm
PHL
-
DEN
9h 30m
1 stop
Frontier Logo
6:05 am - 11:49 am
DEN
-
PHL
3h 44mnonstop
$239Frontier
Wed, Aug 5 - Sat, Aug 8
Frontier Logo
12:44 pm - 2:58 pm
PHL
-
DEN
4h 14mnonstop
Frontier Logo
10:00 am - 7:20 pm
DEN
-
PHL
7h 20m
1 stop
$240Frontier
Tue, Aug 4 - Tue, Aug 11
Frontier Logo
4:30 pm - 10:05 pm
PHL
-
DEN
7h 35m
1 stop
Frontier Logo
6:05 am - 11:49 am
DEN
-
PHL
3h 44mnonstop
$241Frontier
Wed, Sep 2 - Wed, Sep 16
Frontier Logo
4:45 pm - 10:10 pm
PHL
-
DEN
7h 25m
1 stop
Frontier Logo
11:59 pm - 1:12 pm
DEN
-
PHL
11h 13m
1 stop
$242Frontier
Thu, Aug 6 - Wed, Aug 12
Multiple Airlines Logo
12:44 pm - 2:58 pm
PHL
-
DEN
4h 14mnonstop
Multiple Airlines Logo
11:37 pm - 8:22 am
DEN
-
PHL
6h 45m
1 stop
$243Multiple Airlines
Sat, Jul 25 - Sat, Aug 1
Frontier Logo
1:32 pm - 10:28 pm
PHL
-
DEN
10h 56m
1 stop
Frontier Logo
6:30 am - 7:20 pm
DEN
-
PHL
10h 50m
1 stop
$244Frontier
Tue, Aug 4 - Wed, Aug 12
Multiple Airlines Logo
11:06 am - 6:00 pm
PHL
-
DEN
8h 54m
1 stop
Multiple Airlines Logo
11:37 pm - 8:22 am
DEN
-
PHL
6h 45m
1 stop
$245Multiple Airlines
Mon, Aug 10 - Tue, Aug 18
Frontier Logo
4:40 pm - 9:03 am
PHL
-
DEN
18h 23m
1 stop
Frontier Logo
11:59 pm - 12:26 pm
DEN
-
PHL
10h 27m
1 stop
$246Frontier
Useful Info

Good to know

Low seasonJanuary
Cheapest flight$137
Best time to beat the crowds with an average 10% drop in price.
Most popular time to fly and prices are also 15% lower on average.
Flight from Philadelphia to Denver

When to book flights from Philadelphia to Boulder

Are your dates flexible? Find out the best times to travel from Philadelphia to Boulder based on our flight data from the last year. Discover the cheapest month and even day to fly.
Estimated round-trip price

FAQs for booking flights from Philadelphia to Boulder

  • Which airports will I be using when flying from Philadelphia to Boulder?

    When flying out of Philadelphia you’ll be using Philadelphia. Boulder does not have its own airport so you’ll be flying into nearby Denver Intl airport, which is 33.4 mi away.

  • How long does a flight from Philadelphia to Boulder take?

    Direct flights cover the 1,553 miles separating Philadelphia and Boulder in about 3h 55m.

  • How many flights are there between Philadelphia and Boulder?

    17 direct flights run between Philadelphia and Boulder on a daily basis. On average, there are about 124 departures each week.

  • What’s the cheapest day of the week to fly between Philadelphia and Boulder?

    Consider leaving on a Sunday and avoid Saturdays if you are looking for the best rates. For your return to Philadelphia, you’ll find the best rates on Saturdays and the most expensive ones on Mondays.

  • How does KAYAK find such low prices on flights from Philadelphia to Boulder?

    KAYAK is a travel search engine. That means we look across the web to find the best prices we can find for our users. With over 2 billion flight queries processed yearly, we are able to display a variety of prices and options on flights from Philadelphia to Boulder.

  • How does KAYAK's flight Price Forecast tool help me choose the right time to buy my flight ticket from Philadelphia to Boulder?

    KAYAK’s flight Price Forecast tool uses historical data to determine whether the price for a flight to Boulder from Philadelphia is likely to change within 7 days, so travelers know whether to wait or book now.

  • What is the Hacker Fare option on flights from Philadelphia to Boulder?

    Hacker Fares allow you to combine one-way tickets in order to save you money over a traditional round-trip ticket. You could then fly to Boulder with an airline and back to Philadelphia with another airline.

  • What is KAYAK's "flexible dates" feature and why should I care when looking for a flight from Philadelphia to Boulder?

    Sometimes travel dates aren't set in stone. If your preferred travel dates have some wiggle room, flexible dates will show you all the options when flying to Boulder from Philadelphia up to 3 days before/after your preferred dates. You can then pick the flights that suit you best.

  • Which airlines provide the cheapest flights from Philadelphia to Boulder?

    In the last 5 days, the cheapest one-way ticket between Philadelphia and Boulder found on KAYAK was with Frontier for $60. Frontier offered a round-trip connection from $97 and United Airlines from $195.

Top tips for finding cheap flights from Philadelphia to Boulder

  • There is no airport in Boulder. Instead, you’ll be flying into Denver Airport when flying between Philadelphia and Boulder.
  • The cheapest flight from Philadelphia to Boulder was found 28 days before departure, on average.
  • Book at least 1 week before departure in order to get a below-average price.
  • High season is considered to be May, June and July. The cheapest month to fly is August.

Reviews of the top 5 airlines serving Philadelphia to Boulder

 
Need help choosing which airline to fly with from Philadelphia to Boulder? KAYAK airline reviews give an overall score for each airline based on loads of factors, including comfort, boarding, in-flight entertainment and more, to make your decision easier. See airline scores according to verified KAYAK customer reviews.
7.9
SouthwestOverall score based on 4244 reviews
8.6Crew
7.0Food
8.0Comfort
8.1Boarding
7.5Entertainment
Airline reviews

Crew was rude, flight was late, wifi didn't work, no food, basically nothing about this flight was good.

2.0 MediocreIrene, Jun 2026
CMH - DEN
Read more Southwest reviews

Crew was rude, flight was late, wifi didn't work, no food, basically nothing about this flight was good.

Flight was constantly delayed with significant changes in time, it was supposed to get to Colorado Springs at 8:30 PM but it got there after midnight.

Airline is not very senior friendly. Flights are late, forcing us to run to the connecting flight. Food is awful. Wish they would go back to pretzels and peanuts. During flight, pressurization isn’t quite right and all of our ears get plugged. Everything is nickel and dime, charging for boarding, seat selection and legroom. While a screen at the desk in the gate area says check your roll on bag now for free due to space limitation, the employee at the desk will not check the bag without a $100 fee. Insane.

We waited in the airplane for over 45 min for a southwest employee to make the flight. This cause over half the plane to miss their connecting flight in Denver. When we confronted the desk upon arrival, they told us the only flight they had was the next day leaving at 8:50 pm!!! Or they offered to get us to Burbank or LA, but after that we were on our own to get back to Santa Barbara. I paid for a flight from sba to bna bna to sba. My re entry into mom mode has been 💯 rough because of southwest mistake with my flight. And now I’m leaving to Reno tomorrow for a vballl tournament and just discovered that my leg in Vegas has me and my 3 kids on a stand by flight even though I had booked these ticket last year November!! Do better southwest!

I appreciate the staff who allowed me to board though I arrived a little late! Regarding the assigned seating, I had booked my flight before this change and wasn't aware of the change at the time, and so I didn't select a seat at booking as I didn't realize it was relevant. Better communication about the change would have been helpful for preparing.

Sacrament staff are always polite and helpful. Airport is easy to maneuver and boarding is straightforward.

Near 4 hour flight with only 1 service. Had to use call button to request water. Internet and power not working until into flight. Internet would stop working during flight.

The Southwest employees (all two of them) were very nice and cheerful despite the fact the line to self-check a bag (simply drop it off) was hundreds of people long. Thank God I arrived early to the airport because I stood in this line for at least an hour. Once on the flight that had been delayed by an hour, we had no Wi-Fi and thus no entertainment. Finally, I hope the investor strong arm tactics against Southwest pay off in a short-term windfall to your C-Suite because the rest of you are screwed. I have been a faithful Southwest customer for 15 years due to everything you just got rid of. I'm flying to Idaho and Washington in October, both places I used to simply book with Southwest without a second thought now with Frontier (Washington) and United (Idaho) because they offer everything the "new" Southwest does but cheaper and at better times, destinations, etc. This really makes me sad...

For my birthday trip this was my second time ever flying, this trip was the best.

We boarded the flight and set two and a half hours on the jetway. Would have been better if they had not boarded us at all. Plane was hot and it was limited ability to access the restrooms or get a drink of water. Very unpleasant experience

Checking bag at terminal was horrible. No agents to check us in and only 1 kiosk working. Boarding went ok. Crew onboard was very scattered rained. Missed our row while serving and then didn’t see them hardly again.

The entertainment is a bit limited, it would be better if they added some games to play besides the movies and tv shows. But the seats are comfortable and the crew is polite

Food was great. Staff was phenomenal. Seats were a bit hard and could use a lot more entertainment options as far as movies to choose from. WiFi was good. Overall great trip.

Read the fine print. This was my flight home. I booked my flight for the quickest way home. Had a carry-on and a personal item. Same as my outbound flight. Apparently I needed to pre-pay extra for my carry-on. When I checked in, I was told that I had to check it. I said I’ll pay for it, and was told that this wasn’t an option anymore. They said I still had to pay $50 to check my carry-on. I told them I’ll pay whatever to just carry it in as intended. I was not allowed, so eventually I paid $50 to check my carry-on under a plane that was half full, with overhead compartments that were even less full. My white carry-on suitcase was practically destroyed getting from Idaho falls to Denver to Orange County. The low price air fair was a bait and switch. Got me to the gate, made me pay extra, then didn’t even allow me to pay for a carry on. Not to mention that I paid the $8 for WiFi that didn’t work. All to get my suitcase destroyed. I don’t think I’m going to even keep my Untied mileage plus membership and card. Apparently, membership does not have its privileges for this one.

newer aircraft, ability to connect my headset via blue tooth for entertainment.

My husband and I recently had an unfortunate experience with Lufthansa. At the Philadelphia International airport, the ground staff refused to board us because we didn’t have a current visa stamped on our passports for Frankfurt. We completely understand that this was our mistake. we should have double-checked the visa requirements before our trip. However, the issue that upset us most was how the situation was handled by the staff. They told us they would mark it as “boarding denied due to visa issue”, but instead they recorded it as “no show”. Because of that incorrect entry, our return flight was automatically cancelled as well, which caused additional stress and expense. Mistakes can happen, but we expected more transparency and accuracy from a reputed airline like Lufthansa. It would have made a big difference if the staff had been more careful and considerate in documenting the situation correctly.

Everything was good, except the seats in economy were so close together, you could barely get out when the seat in front of your was reclined. If the airlines keep jamming in more and more seats, it will become intolerable. I will look for another airline that considers customer comfort and does not keep adding more rows of seats for more profit.

Flight attendant moved my bag without notifying me and was rude to me when I asked him about it. There was no reason to move it.

Flight was on time, crew were excellent. For some reason our originally selected seats were changed. We had to re-choose our seats when we checked in online and options were limited. One of our two checked bags we placed on the wrong carousel. It was only be shear luck that I saw it. That cost us 20 minutes of wasted time. So much for the “priority” tags. They are meaningless, and have been ever since they were implemented. I wish you would do the save some money and stop using them.

Seats suck. Only one drink service in three hours with the flight attendants being more attendant to their phones than the customer. Painful in the extreme.

Fine. Nothing to write home about. The plane left on time, and arrived on time.

Flight left early and arrived 30 MINUTES early at the destination. Smooth trip.

Flight was 3 hours delayed. They gave our plan to two other routes. Need to knock that off.

The flight was on time and the landing was very smooth. The crew and flight attendants were all very friendly and professional.

Plane was super cold. No entertainment unless you were with mileage program Getting off the plane was super slow

I appreciate that I finally got the seat I paid extra for this time. Thank you

Half of the TSA checkpoints at PHL are closed. Also, there is no standby for first class passengers. You can only standby for coach. Very dated policy and inconsistent with peers.

It would have been nice if American tried to care.

Delayed initially because they couldn’t print the flight details. Poor instruction on delay. When I got on the plane the flight attendant argued with me about whether my carry on would fit (it did, although she didn’t acknowledge that). No greeting (other than arguing with me) getting on or off the plane.

Beverage service was not good. Also just one service in 5 hr 30 min flight. No ask fir water ir anything beside one time beverage service.

When I agreed to give up my two seats because of overbooking by the airline, I should have been offered some sort of reward or credit towards a future flight. I was not. It was not until the next day when I mentioned it to a Jet Blue employee that I was advised to call 1-800-JetBlue. So here I am, having done Jet Blue a favor and I had to do the work to find out if I was going to get a credit. Such service

A nightmare. Scheduled flight delayed 2 hours then cancelled because pilot timed out . Unable to find another pilot. Really?! Weather certainly a factor, but JetBlue seemed totally unprepared for the chaos that ensued when flight routes were cancelled. More cancelled flights, finally many of us who had been bumped from other flights were allowed to board a Boston bound plane around 3:00am, delay after delay, sat on tarmac for another half hour while pilot dealt with weight distribution issues (?), arrived in Boston 4:30. Crew were wonderful- same attendants all day and night and they were exhausted. Fortunately for me and my son that Boston was our final destination, not so lucky for many who missed connecting flights.

Complete and total debacle from start to finish. HUGE mistake picking this airline. NEVER again! Rudest staff in the business.

It's not JetBlues fault but there was a smell on the plane (possibly other travelers) and 3 children behind me that never quit whining. Soccor fans that were very loud. Pilot brought the plane down from high altitude quickly, dropping us hu dress of feet at a time. I've never felt that intense of dropping on other airlines (usually fly Southwest Airlines). But I arrived safely and I'm thankful for that.

Seats were great, the staff was great, and the food was about the best I've had on a plane, and is especially the best of any US-based carrier I've flown. Free Wi-Fi was also great.

The flight was delayed 14 hours and communication was very poor. No one seemed to know what was happening and the gate agent was trying to help people for several flights. She was by herself trying to help 100s of people.

They lost my luggage and refuse to help. Terrible airline. I've never experienced worse customer service in my life. Pretty much just told me too bad that I lost all my luggage, not caring that I am stuck in Europe for 2 weeks with absolutely nothing.

I especially liked the lead crew officer. His boarding and safety announcements were made with a bit of novelty and humor. The flight also left the gate 10 minutes early and we landed about 20 minutes early… It was a delightful flight…

The pilots were awesome and got us there early. Great landing too. No complaints on the flight. Service - a young cabin crew woman was terrible as she seemed to hate her job and never smiled. Why do they hire people like that? Terrible. The cabin crew lead woman was wonderful - very professional (and more mature go figure)

As with all airline's seats, a little more padding would appreciated. Especially on longer flights.

I am writing to express my disappointment with my recent Frontier Airlines flight. I was charged $99 at the gate because my bag was said to be too large, yet once onboard there was no available overhead bin space, and I was required to place the bag under the seat in front of me anyway. This made the charge feel unnecessary and unfair. Additionally, before the flight even took off, I was asked to move from the seat I paid for into a middle seat so another passenger and her cat could have my seat to themselves. I was not offered compensation or an explanation for being moved from a paid seat. Between the unexpected bag fee and being forced to give up my seat, this experience fell well below acceptable customer service standards. I would appreciate a review of this situation and appropriate compensation.

Terrible. Flight cancelled with no reasoning and no flights to rebook. Employees were useless and did nothing to help. Did not even know where to retrieve luggage from the cancelled flight. Flyers beware.

sluggish boarding and arrival procedures, fake nice flight attendants, and lots of delays.

You get what you pay for nothing essentially but a hard uncomfortable seat that doesn’t recline and kids screaming all around you and chaotic boarding and limited check bag weight allowance when compared to other airlines

Not very good. Paid in excess of $400 for assigned seating for my family and that was not provided. I want that money back.

Check in at Philadelphia international was absolutely terrible! I fly 2 to 3 times a month and avoid frontier at all cost and will never fly Frontier again! The night before travel, I tried checking in however, the app was giving me an error, so I went to the desktop, which instructed you that you need to use the app. The next day I presented at the check-in gate after trying at least a half dozen times prior to getting into the airport and continuing to getting the error in the app. I actually had rebooted my phone numerous times and reinstall the app just in case. My phone is only one generation older than the current model. It has no problems completing a frontier flight purchase or any other app issues. There was only three frontier employees working at check-in and a huge line while I was in line I continued to try and check in via the app. As I approach the desk, I was dreading dealing with the agent. He was extremely unprofessional, anti-semantic & very ignorant, and mean to the people in front of me, as well as the people who ended up being behind me. He literally told people “Man I don’t care bout y’all” in his native dialect! Maintaining my composure I approached and explained the situation. To which he replied, you’re gonna have to pay then! I don’t understand. It’s an issue with their app not allowing me to check in! Not my issue! He told me if I pay cash it would be $15, $25 if I pay credit card. I don’t understand a $10 difference for paying with a credit card? I am completely cashless so I continued to try using the app to avoid the $25 fee, Which I still don’t believe that I should be responsible for since it was Frontier’s technical issue!!! I continued to check in via the app a couple more times after he verified I was doing everything right he proceeded to continue to belittle the people behind me. Yelling at them saying I don’t care about you people! I cannot believe that this is the way that businesses would treat its customers! Unfortunately, the black mail with dreadlocks did not have a name tag all he had was a frontier sweater on! For the $25 fee that I ended up getting charged on my credit card. I should’ve just booked originally with Spirit or any other carrier! I have no problem paying fees that I should be responsible for, but when it’s due to a technical failure of a company, the customer should not be responsible for it! I cannot believe that it’s not frontier going out of business!

terrible cascading delays and unhelpful customer service. uncomfortable plane. crew was great, however!

Booked direct in July '24. Turned into a 14 hr layover (both ways) in Denver. My 5 day vaca turned into a 1 day . Not good, BUT,... Thank you for the people @ Frontier who were professionally friendly & approachable.

$80 fee for a backpack as a personal item is robbery.

Flying Frontiier was extremely poor!! I paid for a7:15am flight on flight 1601 from PHL To Las Vegas and the delay was brutally, excruciatingly and disgustingly long (8 hrs). I arrived by Uber to PHL at 5:30 am and had to spend the entire 8 hr delay inside the airport. Even more atrocious was that the flight was delayed twice. On the phone with customer service for two hours and was not fully compensated. I feel taken advantage of with this airline. They offered a menial couched for another flight within 90 days to me and my husband who has never flown but this experience has made us almost 100% sure to not fly this airline and will suggest that others don’t either. We don’t want to book ever again, don’t want a menial voucher and I believe by standard and because the flight was delayed for 8 hours, I should be fully reimbursed for the entire round trip. There is no excuse why this should have ever occurred. After sharing my experience with others in Vegas and Philadelphia, I was told that Frontier airlines is notorious for long delayed flights, poor customer service and refusal to compensate people correctly. I’m very nervous to see what departing from Vegas to Philadelphia will bring.

Everything you need to know for your flight from Philadelphia to Boulder

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