What happens if I miss a connection on a self-transfer?

This is the most important page in this help centre. Read it before you book anything with more than one booking reference.

Protected: every flight is on one ticket. If the first leg is late and you miss the second, the airline rebooks you at its cost. That is what the through-fare is partly paying for.
Self-transfer: the flights are on separate tickets. If the first leg is late, the second airline sees a passenger who did not show up. It owes you nothing. A new ticket, that night's hotel and the bag are all yours.

Every trip carries a protection label. Legs sold together on one ticket are marked protected. Anything assembled from separate bookings is marked self-transfer, always, with no soft wording.
Connection buffers are computed in real time, in UTC, using each airport's own timezone, and they are shown on the journey page.
Under two hours between separate tickets, the trip is treated as risky. It can still appear on screen, but it is never alerted on.
Under four hours at the same airport, or under twelve hours across two airports in the same city, you get a warning on the trip.

Leave much more time than feels necessary. Half a day at a hub is cheap insurance next to a walk-up fare.
Prefer the first flight of the day for the first leg. Delays accumulate through the day.
Check whether your bag is through-checked. On separate tickets it usually is not, so you need enough time to collect it and check it in again.
Two airports in one city is a real journey. London Stansted to Heathrow is a couple of hours of your day, and that is why the warning threshold there is twelve hours.
Consider travel insurance that covers missed connections on separate tickets. Many policies specifically do not.

Fare Sniper shows you the trade and prices it. It cannot take the risk for you, and it is not liable for a missed connection. See the terms.