How reliable is Seattle Tacoma International Airport?
Flights from SEA departed within 15 minutes of schedule in 82% of 1,080,467 flights in official BTS history — and weather is calmest in Jul. Here’s the full picture before you book.
Reliability score
on-time, cancellations & delays
Weather favorability
year-round climate
Origin-airport operations
What the departure punctuality at SEA looks like
On-time departures
across 1,080,467 flights
Source: BTS Airport Operations · data through 2026-06-25. Role-specific BTS departure history; advisory context, not a guarantee for any flight.
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Weather by month
When the weather works for you at Seattle
A calm-weather score (0–100) for each month from decades of airport observations — how often conditions disrupt flying, not temperature. Higher is calmer.
Calmest month
Calmest flying weather of the year · 98/100 favorability
Roughest month
Most disruptive — low visibility & fog, snow · 83/100 favorability
Connecting through SEA
How much layover you really need
Allow at least this between domestic flights at SEA. Below it, one small delay risks a misconnect.
International transfers add immigration and bag recheck — give yourself this buffer at SEA or more.
PlaneSane connection-time estimate tuned for SEA's terminal layout. We score every connecting itinerary against conservative connection floors.
The read on SEA
What the numbers say about flying through Seattle Tacoma International Airport
Across official performance history, flights from Seattle left within 15 minutes of schedule about 82% of the time over 1,080,467 flights. That's a solid, better-than-average operational record. Pair it with a low cancellation rate of 1.1%, so flights here rarely vanish outright. When a departure does run late, the typical delay is around 9 minutes.
On weather, Seattle is an unusually calm-weather airport year-round. July is the calmest stretch for flying, scoring 98 out of 100 for favorable conditions, while December is the most disruptive at 83, driven mainly by low visibility & fog and snow. The year is relatively steady, so no single month stands out as one to avoid on weather alone.
If you're connecting through SEA, give yourself room. A domestic connection wants at least about 45 minutes, and international transfer wants roughly 95 minutes once immigration and a bag recheck are in the mix. Those are floors, not comfortable buffers — one inbound delay can erase them, so add margin when the connection matters.
None of this guarantees your specific flight — it’s the backdrop. To turn it into a booking, score real flights to Seattle, read how we weigh it all in how the PlaneSane Score works, and brush up with how to pick a reliable flight and avoiding weather delays.
Common questions about SEA
- How reliable is Seattle Tacoma International Airport (SEA)?
- Flights from Seattle left within 15 minutes of schedule roughly 82% of the time across 1,080,467 flights of official history — a solid, better-than-average operational record. The cancellation rate runs about 1.1%. It's advisory context, not a guarantee for any single flight.
- What is the best month to fly from SEA for good weather?
- July has the calmest flying weather at Seattle Tacoma International Airport. December is the most disruptive, mainly from low visibility & fog and snow.
- How much layover time do you need at SEA?
- Allow at least about 45 minutes for a domestic connection and about 95 minutes for an international one as a floor. These are minimums, not comfortable buffers — a single inbound delay can wipe them out, so add margin when you can.
Planning a trip through Seattle?
Score real flights to and from SEA on reliability, weather, and connection safety — not just price.