Frontier offers extra comfort seats with 32” separation for a fee, ideal for taller passengers.
Frontier's Board First option allows early boarding for carry-on bag purchasers and elite members.

Most accurate provider | CheapOair 3 stars |
|---|---|
Most trusted provider | CheapOair 3 stars |
Round-trip from | $129 (Delta) |
One-way from | $76 (Southwest) |
Popular in | July |
Cheapest in | January |
Average price | $214 |
Good round-trip deal | $194 or less |
Good one-way deal | $118 or less |
Fly from
Fly to
Route
Depart
Return
Price
OntarioSeattle
ONT - SEA
ONTSEA
Ontario
Wed 12/17
5:49 pm-8:49 pm
Nonstop3h 00m
Seattle/Tacoma Intl
Tue 1/6
11:25 am-4:13 pm
1 stop4h 48m
OntarioSeattle
ONT - SEA
ONTSEA
Ontario
Tue 12/16
4:49 pm-11:25 pm
1 stop6h 36m
Seattle/Tacoma Intl
Thu 1/8
11:15 am-1:56 pm
Nonstop2h 41m
OntarioSeattle
ONT - SEA
ONTSEA
Ontario
Thu 12/4
4:49 pm-12:21 am
1 stop7h 32m
Seattle/Tacoma Intl
Tue 12/9
2:19 pm-5:07 pm
Nonstop2h 48m
OntarioSeattle
ONT - SEA
ONTSEA
Ontario
Sun 12/14
6:40 am-9:45 am
Nonstop3h 05m
Seattle/Tacoma Intl
Tue 1/6
5:25 am-12:16 pm
1 stop6h 51m
OntarioSeattle
ONT - SEA
ONTSEA
Ontario
Fri 1/23
3:30 pm-6:35 pm
Nonstop3h 05m
Seattle/Tacoma Intl
Mon 1/26
7:00 pm-11:58 pm
1 stop4h 58m
OntarioSeattle
ONT - SEA
ONTSEA
Ontario
Thu 12/11
5:49 pm-8:49 pm
Nonstop3h 00m
Seattle/Tacoma Intl
Mon 12/15
7:11 pm-11:58 pm
1 stop4h 47m
OntarioSeattle
ONT - SEA
ONTSEA
Ontario
Thu 12/18
5:49 pm-8:49 pm
Nonstop3h 00m
Seattle/Tacoma Intl
Sat 1/17
5:25 am-12:16 pm
1 stop6h 51m
OntarioSeattle
ONT - SEA
ONTSEA
Ontario
Sat 12/6
6:40 am-9:45 am
Nonstop3h 05m
Seattle/Tacoma Intl
Mon 12/8
7:11 pm-11:58 pm
1 stop4h 47m
OntarioSeattle
ONT - SEA
ONTSEA
Ontario
Sat 12/6
4:49 pm-11:25 pm
1 stop6h 36m
Seattle/Tacoma Intl
Sun 12/7
8:30 am-11:13 am
Nonstop2h 43m
OntarioSeattle
ONT - SEA
ONTSEA
Ontario
Fri 1/9
11:10 am-4:00 pm
1 stop4h 50m
| Provider | Price Accuracy | Trust Score* |
|---|---|---|
| Price Accuracy2 stars | Trust Score*3 stars | |
| Price Accuracy3 stars | Trust Score*1 star | |
| Price Accuracy3 stars | Trust Score*3 stars | |
| Price Accuracy3 stars | Trust Score*2 stars | |
| Price Accuracy3 stars | Trust Score*3 stars | |
| Price Accuracy3 stars | Trust Score*3 stars | |
| Price Accuracy- | Trust Score*1 star | |
| Price Accuracy3 stars | Trust Score*3 stars | |
| Price Accuracy3 stars | Trust Score*3 stars | |
| Price Accuracy3 stars | Trust Score*3 stars |
To ensure you get the cheapest price possible for a flight from Ontario to Seattle, you should look to book at least 55 days in advance of your intended travel date. The price of your flight may increase if you delay and leave booking until a week or so before departure.
Currently, January is the cheapest month in which you can book a flight from Ontario to Seattle (average of $38). Flying from Ontario to Seattle in July is currently the most expensive (average of $134). 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.
It’s typically best to fly out from Ontario to Seattle in the morning. Doing so could potentially save you 15% on the flight price compared to flying at noon, which is usually more expensive.
Travelers seeking maximum savings on their Ontario to Seattle flight should consider departing on Friday mornings 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.
About 6% of weekly flights between Ontario and Seattle have experienced delays in the past year, with the average delay time being 133 minutes.
Historically, flights departing at night are less likely to be delayed, whereas flights leaving in the evening tend to experience delays more often.
Wednesday tends to have the lowest number of delays on this route, whereas Friday has historically faced a higher average of delays compared to other days of the week.
Over the last year, Scandinavian Airlines have had the lowest number of delays on this route, with just 2% of flights being delayed.
Entertainment
Crew
Food
Comfort
Overall
Boarding
Reviews
Anonymous,Aug 2025
MFR - SEA
Entertainment
Crew
Food
Comfort
Overall
Boarding
Reviews
Anonymous,Aug 2025
MFR - SEA
Entertainment
Crew
Food
Comfort
Overall
Boarding
Reviews
Anonymous,Aug 2025
MFR - SEA
Entertainment
Crew
Food
Comfort
Overall
Boarding
Reviews
Anonymous,Aug 2025
MFR - SEA
Entertainment
Crew
Food
Comfort
Overall
Boarding
Reviews
Anonymous,Aug 2025
MFR - SEA
Entertainment
Crew
Food
Comfort
Overall
Boarding
Reviews
Anonymous,Aug 2025
MFR - SEA
| Airline | Cheapest | Average | Flexibility | On-time |
|---|---|---|---|---|
| Cheapest$83 | Average$174 | FlexibilityNo cancel fee | On-time62% | |
| Cheapest$98 | Average$248 | FlexibilityNo cancel fee | On-time85% | |
| Cheapest$120 | Average$256 | FlexibilityNo cancel fee | On-timeN/A | |
| Cheapest$150 | Average$266 | FlexibilityNo cancel fee | On-time75% | |
| Cheapest$150 | Average$256 | FlexibilityNo cancel fee | On-time63% |