Flying San Francisco → Hong Kong: Do You Lose or Gain a Day?

You gain a day.

Time zones: San Francisco = UTC−8 (PST) / UTC−7 (PDT). Hong Kong = UTC+8 (HKT, no DST). Difference = 15–16 hours ahead.

Example: Depart SFO 9:00 PM Monday (15h flight). Arrive HKG 10:00 AM Wednesday. You've "lost" a calendar day locally, but actually gained hours relative to origin.

West-to-east travel across the Pacific date line adds a day. Returning east-to-west, you "repeat" a day.