In 2026, the short answer is: usually no, but you will need it soon after. Most major airlines (like British Airways, Emirates, and United) allow you to complete a booking and pay for your ticket using only your full name (as it appears on your passport), date of birth, and contact information. You can skip the passport details during the initial transaction. However, you must provide your passport number, expiry date, and country of issue during the "Advance Passenger Information" (API) or "Manage My Booking" phase, and certainly before you can check in online. Some specific low-cost carriers or airlines flying into high-security regions (like China or certain Middle Eastern nations) may require the passport number at the time of purchase to verify your identity against "No Fly" lists immediately. If you are renewing your passport, it is perfectly safe to book the flight with your old details (or skip the step) and update the record once your new passport arrives, provided the name on the booking remains identical to the name on the new document.