How reliable is Ontario International Airport?
Flights from ONT departed within 15 minutes of schedule in 84% of 146,123 flights in official BTS history — and weather is calmest in Aug. 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 ONT looks like
On-time departures
across 146,123 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 Ontario
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, high winds · 90/100 favorability
The read on ONT
What the numbers say about flying through Ontario International Airport
Across official performance history, flights from Ontario left within 15 minutes of schedule about 84% of the time over 146,123 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, Ontario is an unusually calm-weather airport year-round. August is the calmest stretch for flying, scoring 98 out of 100 for favorable conditions, while December is the most disruptive at 90, driven mainly by low visibility & fog and high winds. The year is relatively steady, so no single month stands out as one to avoid on weather alone.
None of this guarantees your specific flight — it’s the backdrop. To turn it into a booking, score real flights to Ontario, 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 ONT
- How reliable is Ontario International Airport (ONT)?
- Flights from Ontario left within 15 minutes of schedule roughly 84% of the time across 146,123 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 ONT for good weather?
- August has the calmest flying weather at Ontario International Airport. December is the most disruptive, mainly from low visibility & fog and high winds.
Planning a trip through Ontario?
Score real flights to and from ONT on reliability, weather, and connection safety — not just price.