Booking a flight for someone else vs booking the same flight

These are two different problems. Booking a flight for someone else means paying for a ticket in their name so they can travel — you may not be going at all. Booking the same flight as someone else means they are already booked, and you want a seat on that same aircraft. Google mixes the two constantly. Here is each one, briefly.

Booking a flight for someone else

Every major airline allows this. There is no requirement that the payment card belongs to the passenger, and no "guest booking" mode you need to find — you simply enter their details instead of yours during checkout.

• Enter their full name exactly as it appears on the passport or government ID they will travel with, including middle names where the ID shows one. Name changes after ticketing are difficult and usually paid; spelling corrections are easier but not guaranteed.
• You will need their date of birth, and for international travel their passport details.
• Use an email address and phone number they can actually reach, or forward the confirmation the moment it arrives — that is what they show at check-in.
• Add their frequent flyer number if they have one, so the miles credit to them rather than disappearing.
• Some airlines ask for a credit card authorisation form or the physical card at check-in when the card holder is not travelling. This is rare but it happens on a few international carriers — check before you fly.

If you are booking for them and travelling with them, put both passengers on the same reservation. One record means one price rule, one set of seats, and no linking phone call.

Booking the same flight as someone else

This is the opposite situation: their ticket already exists and you want to join them. You need three things from their confirmation — the airline, the flight number and the departure date — and nothing else. Their name and record locator are irrelevant to you.

Search that route and date, filter to that airline, match the departure time, confirm the flight number, and buy. The full walkthrough, including codeshares and connections, is in how to book the same flight as someone else. Or skip the searching entirely and drop a screenshot of their confirmation into SameFly, which reads the flight number and sends you to that exact flight.

Two things follow from doing it this way. You will almost certainly pay a different fare than they did, because fares move. And you will end up on a separate reservation, which means seats together are not automatic — you will want to link the two reservations by phone.

The question people actually mean

When someone asks "can I add them to my booking?", they are usually in the second situation and hoping for the first. The answer is no: you cannot add a passenger to an existing flight reservation. Book a second ticket on the same flight, then link them. The only exception is a lap infant, who can normally be added to an adult's existing booking by phone.