Parabola Calculator

Analyse a parabola y = ax² + bx + c — vertex, axis of symmetry, focus, directrix and intercepts — with everything marked on a graph.

y = x2 + x +
Vertex
Axis of symmetry
Focus
Directrix
x-intercepts
y-intercept

How to Analyse a Parabola

Enter the coefficients a, b and c to get the vertex, focus, directrix and intercepts.

1

Enter the quadratic

Type the coefficients of y = ax² + bx + c. a must not be zero for the graph to be a parabola.

2

Read the key features

The vertex is at x = −b ⁄ (2a); the axis of symmetry passes through it. The focus sits 1 ⁄ (4a) above the vertex and the directrix the same distance below.

3

Read the intercepts

The x-intercepts are the real roots of the quadratic (there may be two, one or none), and the y-intercept is (0, c).

Frequently Asked Questions

How do you find the focus and directrix of a parabola?
For y = ax² + bx + c with vertex (h, k), the focus is (h, k + 1 ⁄ (4a)) and the directrix is the line y = k − 1 ⁄ (4a). The focus is inside the curve and the directrix is the mirror line the same distance away.
What are the x-intercepts of a parabola?
They are the x-values where y = 0 — the real roots of ax² + bx + c. A parabola can cross the x-axis twice, touch it once, or not at all, depending on the discriminant b² − 4ac.
What is the y-intercept of a parabola?
The y-intercept is where x = 0, which gives y = c. So the parabola always crosses the y-axis at (0, c).
What is the axis of symmetry?
It is the vertical line x = −b ⁄ (2a) through the vertex; the parabola is symmetric across it.
Is my data sent anywhere?
No. Everything runs in your browser with JavaScript; nothing you type is uploaded or stored.