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Slope Calculator

Point 1 (x1, y1)

Point 2 (x2, y2)

m = (y2 - y1) / (x2 - x1)

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Reviewed by Dr. Alex M., Ph.D.

Last updated: November 2025

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💡 Expert Tips

Order Matters (But Not Really)

You can subtract Point 1 from Point 2 OR Point 2 from Point 1. The key is consistency. If you start with y2 on top, you MUST start with x2 on the bottom. (y2-y1)/(x2-x1) gives the same answer as (y1-y2)/(x1-x2).

Watch for Negatives

Subtracting a negative number turns into addition. For example, 5 - (-3) becomes 5 + 3 = 8. This is the #1 source of errors in slope calculations. Use parentheses if it helps!

Zero in the Denominator

If x2 - x1 = 0, you are dividing by zero. This means the line is vertical (straight up and down). In math, we call this slope "Undefined".

⚠️ Common Mistakes

Mixing X and Y

Remember: Rise (Y) over Run (X). The Y values always go on top (numerator), and X values go on the bottom (denominator). A common mistake is flipping them.

Swapping Points

Don't mix up the order. You can't do (y2 - y1) / (x1 - x2). If you use Point 2 first on top, you must use Point 2 first on the bottom.

Confusing Zero and Undefined

A horizontal line (flat) has a slope of 0. A vertical line (up/down) has an undefined slope. They are completely different concepts!

❓ Frequently Asked Questions

What is the slope formula? +

The slope formula is m = (y₂ - y₁) / (x₂ - x₁). It represents the change in Y divided by the change in X, often called 'rise over run'.

What does a slope of 0 mean? +

A slope of 0 means the line is perfectly horizontal (flat). There is no 'rise', only 'run'. For example, the line y = 5 has a slope of 0.

What is an undefined slope? +

An undefined slope occurs when the line is vertical. This happens because you would be dividing by zero (the 'run' is 0). Vertical lines like x = 3 have undefined slopes.

How do I find slope from an equation? +

If the equation is in slope-intercept form (y = mx + b), the slope is the number 'm' in front of x. For example, in y = -2x + 4, the slope is -2.

What is 'Rise over Run'? +

'Rise' is the vertical change (difference in Y values), and 'Run' is the horizontal change (difference in X values). Slope is simply the ratio of Rise to Run.