How a cut stair stringer is laid out — framing-square steps, throat depth, and why it shears

What this diagram shows

A 2-by-12 cut (notched) stair stringer drawn at the stair angle. A framing square lays out each step, with the riser height marked on one leg and the tread run on the other. The throat — the wood remaining behind each notch, measured perpendicular to the bottom edge — must stay at least 5 inches, because a cut stringer fails in shear at the inside corner of a notch (the stress riser) before it ever reaches its bending limit. The top of the stringer is a plumb cut bearing against the header, and the bottom riser is dropped by one tread thickness so every finished riser ends up equal. A cut stringer spans about 6 feet of run (SPF) before it needs support.