Free · Coordinate geometry calculators 📈

Segment Endpoint from Midpoint and Known Endpoint

Yes. In that case both endpoints coincide and the segment has zero length. Otherwise subtract the known endpoint from twice the midpoint, independently on each Cartesian axis.

Formula & worked example
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Calculator inputs

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How to use this calculator

Enter the known values in the units shown. Results update as you type.
Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
Use the worked example to check the method. Reset restores the starting fields.

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Formula and method

Example in initial displayed units: x₁ -2, y₁ 1, x 1, y 3 gives x₂ 4, y₂ 5.

B = 2M−A; M = (A+B)/2

Worked example

Enter these known values and leave the other values blank.

x₁: -2
y₁: 1
x: 1
y: 3

x₂: 4
y₂: 5

Assumptions and limitations

The midpoint bisects a segment on a Cartesian plane. Coordinates may be negative, and each axis solves independently. Equal endpoint and midpoint coordinates describe a degenerate segment with both endpoints at one point.
Use compatible units and enough independent values. Clear unknowns before solving backward. Original reference drawings are schematic and do not scale to entered values.

Common questions

Can an endpoint and midpoint be the same point?