Equation of a line calculator

Find the line through two points: slope = (y₂ − y₁)/(x₂ − x₁), then y = mx + b.

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First x

First y

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Second x

Second y

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Answer

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Two points give m = (y₂ − y₁)/(x₂ − x₁), then b = y₁ − mx₁. Point-and-slope mode gives b = y − mx; slope-and-intercept mode uses y = mx + b directly.

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Formula and assumptions

Identical points cannot define a unique line. Vertical lines return x = constant rather than dividing by zero.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-26

Using Equation of a line calculator

Two points give m = (y₂ − y₁)/(x₂ − x₁), then b = y₁ − mx₁. Point-and-slope mode gives b = y − mx; slope-and-intercept mode uses y = mx + b directly.

Identical points cannot define a unique line. Vertical lines return x = constant rather than dividing by zero.

Next: Slope calculator

A worked example

Example inputs: first x = 1, first y = 3, second x = 3, second y = 7. Line equation = y = 2x + 1.

Before you use the result

Identical points cannot define a unique line. Vertical lines return x = constant rather than dividing by zero.

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