Percent Calculator

Percent Formula

Worked Example

15% of 80:

1. P% of X = (P ÷ 100) × X
2. = 0.15 × 80 = 12

Test-day tip

SAT percent questions often chain changes: a 20% increase then a 20% decrease is ×1.2 × 0.8 = 0.96, a net 4% decrease. Multiply the factors instead of adding the percents.

More Algebra Calculators

• Slope Calculator

  m = (y₂ − y₁) ÷ (x₂ − x₁)

  rise over run between points (x₁, y₁) and (x₂, y₂)

  Example: The line through (1, 2) and (4, 8): Slope m = 2.

  Open the slope calculator →

• Slope-Intercept Form Calculator

  y = mx + b

  m slope, b y-intercept = y₁ − m·x₁

  Example: The line through (1, 2) and (4, 8): Slope-intercept form: y = 2x.

  Open the slope-intercept form calculator →

• Point-Slope Form Calculator

  y − y₁ = m(x − x₁)

  point (x₁, y₁), slope m

  Example: The line through (1, 2) with slope 3: Point-slope form: y − 2 = 3(x − 1).

  Open the point-slope form calculator →

• Systems of Equations Calculator

  a₁x + b₁y = c₁, a₂x + b₂y = c₂

  solved by elimination / Cramer’s rule; determinant 0 means no unique solution

  Example: The system 2x + 3y = 12 and x − y = 1: Solution: x = 3, y = 2.

  Open the systems of equations calculator →

Frequently asked questions

Sources

Last reviewed: 2026-10-15. Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.