Upvote:2
The question for baggage depends on how you book your ticket; if it is from one airline for the entire trip, or is it multiple airlines (that you booked individually).
The easy case is if you booked one ticket, which means you have one carrier, in that case, for your outbound trip:
For your return trip:
You only pay to have your bags checked if they are above the weight or item limit for your itinerary; which is dictated by the class of travel and the airline you are using. There is no universal rule, except that the airline that you are using for the majority of the trip - its fare conditions will apply for the remainder of your trip.
If you have booked multiple tickets on different airlines, then each time you switch airlines, you may have to collect your bags. Some airlines have interline agreements (basically, an agreement between two different airlines to accept each others' checked bags). Chances are high that you will have to pay extra fees if your baggage exceeds the allowance for that leg of your journey.
The best course of action is to ask the agent when you first start your journey, they will have the most up-to-date information.