Most people underestimate this one. LaGuardia looks close on a map, but the Grand Central Parkway and the roads around the terminals can back up quickly. A reasonable guide: Domestic flights: leave about 2.5 hours before departure Weekday rush hour or bad weather: add 30 to 45 minutes Traveling with kids or heavy luggage: add another 15 to 20 minutes A local chauffeur will usually suggest a pickup time based on current traffic, which is more reliable than a fixed rule. When you book a New York airport limousine service, give them your airline and terminal so they can plan the best route. For disclosure, I am affiliated with Carmellimo, which serves the New York airports. Their homepage has booking details.