Important Math Formulas on the ACT

You won’t see a formula sheet on the ACT Math section, so there are a few math formulas you need to memorize and recall when you take the ACT test. 

Often, knowledge of these key formulas can help you solve problems faster and more accurately. Below, you’ll find a list of ACT math formulas to know from every content area in the Math section: Numbers and Quantity, Algebra and Functions, Statistics and Probability, and Geometry.

At the end of the post, you can find a downloadable ACT formula sheet in PDF format.

Important ACT Math Formulas

Number and Quantity


Calculating percents:

act math example

or, change the words to an algebraic equation and solve:

Example: 40% of what is 20?

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Percent increase or decrease:

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Exponents and Roots

act math example
act math example

Complex Numbers

act math example

Use the conjugate to eliminate the imaginary: 

act math example

Arithmetic Sequences

Each term (t) is the previous term plus a common difference (d) to find the nth term

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Geometric Sequences

Each term (t) is the previous term times a common ratio (r) to find the nth term

act math example

Statistics and Probability

Mean (the average)

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The middle value when items are arranged from least to greatest


The difference between the max value and min value


The value that occurs the most in a set 

Standard Deviation

Shows how spread the data points are.

Low standard deviation: 

Data points are closer to the mean

High standard deviation: 

Data is spread over a wider range

Probability of an Event

act math example

Joint or Conditional Probability

Mutually Exclusive Probability

Fundamental Counting Principle

Pick 1 from each group, multiply the number of options in each group


A combination of events occurring when order matters and the items cannot be repeated


A combination of events occurring when the order does not matter


Set of possible values of x


Set of possible values of y

Algebra and Functions


The slope of a line:

Parallel lines:

Have the same slope

Perpendicular lines:

Have slopes that are negative reciprocals

Slope-Intercept Form

Point-Slope Form

Midpoint Formula

Distance Formula

Direct Variation

y=kx where k is the constant of variation

Indirect Variation

yx=k where k is the constant of variation

Standard Form of a Quadratic

To find the solutions: Set y equal to 0, and solve for x by factoring or use the Quadratic Formula:

To find the vertex:  x = -b/2a, plug value back into the equation to find the y-coordinate  

Vertex Form of a Quadratic

The vertex is (h, k ).

Factored Form of a Quadratic

x-intercepts/solutions/zeros are x=p & x=q

Exponential Functions

Shows growth if b>1or decay if 0<b<1

Growth/Decay when r  is a percent:

Change to decimal, add to 1 if growth, subtract from 1 if decay

Interest compounded n times for t  years:

Interest continuously compounded for t  years: 

Some Helpful Log Rules



Degrees sum to 180°  


No side can be greater than the sum or less than the difference in length of the other two. Side lengths are in the same ratio as opposite angle measures.


Complementary angles sum to 90°

Supplementary angles sum to 180°

Exterior angles for ANY polygon sum to 360°.

Interior angles for a polygon sum to 180° (n-2) where n is the number of sides in the polygon.

Special Right Triangles

30, 60, 90 Triangle

45, 45, 90 Triangle

Rectangular Prism


Trigonometric Ratios

Remember these ratios with the acronym “SOH-CAH-TOA”

Trigonometric Relationships


Standard Form of a Circle

Vertex Form of a Circle

(h, k) is the center and r is the radius

Download the PDF version of this list of ACT formulas:

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