Endpoint Calculator

What the Endpoint Calculator Does

Geometry problems often hand you half a line and expect you to finish it. The Endpoint Calculator takes the Starting point coordinates and the Midpoint coordinates you already know, and pressing Calculate endpoint reveals the other end of the segment exactly.

Students doing coordinate geometry, CAD drafters, surveyors, and game programmers meet this setup constantly. Whenever a segment’s start and its center are pinned down, the finish point follows from pure arithmetic, with no trial and error required at all.

The Formula and a Worked Example

The reasoning follows the midpoint idea, since a midpoint is the average of the two endpoints. Rearranged, the endpoint formula is endpoint = 2 x midpoint – other endpoint, applied separately to x and y. Doubling the midpoint and then subtracting the known point lands you on the unknown one.

Worked example: let the starting point be (2, 3) and the midpoint be (7, 5). The x answer is 2 x 7 – 2 = 12, and the y answer is 2 x 5 – 3 = 7, so the missing endpoint is (12, 7). Checking confirms (7, 5) sits exactly halfway between the pair.

How to Use It and Practical Tips

Enter the Starting point coordinates, then the Midpoint coordinates in the same order, and press Calculate endpoint. Both points must live in one coordinate system with one unit, whether pixels, meters, or map degrees, because coordinates from different systems cannot combine.

Quick self check: subtract the starting point from the midpoint and add that offset to the midpoint again. If you land on the computed endpoint, everything is consistent, since the midpoint always splits a segment into two perfectly equal halves.