How to Use the Endpoint Calculator

Enter one known endpoint and the midpoint of the segment. The other endpoint's coordinates come out below.

x2 = (2 × midpoint x) − x1
y2 = (2 × midpoint y) − y1

This runs the midpoint formula in reverse — if the midpoint is the average of both endpoints, then doubling it and subtracting the known endpoint isolates the one that's missing. It's the same algebra a surveyor or a CAD program applies constantly: knowing a segment's center and one end is functionally the same as knowing both ends outright.