Load-bearing walls enforce a home's structure by bearing the weight of upper levels and/or a roof plus additional snow load -- similar to the way large bones support a body. All exterior walls are load bearing, but typically, only some interior walls support weight; the rest simply separate interior spaces. A building inspector has the final say on whether a wall is load bearing or not, but it is possible to scout out possible load-bearing walls yourself by looking at a few of your home's structural features. However, there are many variables, including previous remodelling and additions to a home, leaving no sure-fire way to be certain without a professional's help.
Look inside the attic space to see which direction the ceiling joists go. Load-bearing interior walls typical run perpendicular to joists. Walls running parallel to joists usually are not load bearing.
Determine a basement or crawlspace support beam's direction by locating the upper beams running along the ceiling, or on the underside of the above floor in an unfinished lowest-level space. Metal telescoping posts, or wood or concrete posts or blocks support upper levels and typically are braced between the beams and the basement or crawlspace floor. Load-bearing walls in the levels above often run the same direction as the lower level's beams.
Read your home's blueprints if you have them. As long as the contractor did not make any changes in your home's structural construction, the load-bearing walls will be evident in the prints.
Pull up floorboards or take down a section of ceiling as a last resort to determine your home's structural supports and load-bearing walls. To determine is an interior wall is a load-bearing wall, you need to see the full length of the home's structural skeleton.