Interpreting slope
A positive slope rises from left to right. A negative slope falls from left to right. A slope of zero is horizontal. A vertical line has undefined slope because the run is zero.
Example
For points (1, 2) and (5, 10), rise is 10 - 2 = 8 and run is 5 - 1 = 4. The slope is 8 / 4 = 2, so y increases by 2 for each 1 unit increase in x.
Common mistakes
Keep the point order consistent. If you subtract y2 - y1, also subtract x2 - x1. Mixing the order can flip the sign.
Limitations
The y-intercept shown is from the line equation y = mx + b. A vertical line has no finite slope-intercept form because x is constant.
Last reviewed: 2026-05-17