How to Use the Inverse Tangent Calculator

Enter any real number. The angle whose tangent equals that value comes out in degrees or radians, whichever is selected.

θ = tan⁻¹(x),  for any real x

"Inverse tangent" and "arctangent" are the same function by two names, and it's the one inverse trig function with no input restriction at all — tangent itself can output any real number, so its inverse has to accept any real number back. By convention the result stays between −90° and 90° (excluding the endpoints), which is also why atan2 exists as a separate function in most programming languages: plain arctangent can't tell a point in one half of the plane from its mirror image on the other side.