SAT / ACT Prep Online Guides and Tips

Guide to ACT Calculators: Expert Tips

Posted by Courtney Montgomery | Jun 19, 2015 11:41:44 PM

ACT Math


Feature_calculator.jpgKnowing when where and how to best use a calculator on the ACT can be tricky. You are allowed to bring a calculator on test day (none will be provided for you), and it can mean the difference of several points on the ACT to have a calculator versus having none.

But what kind of calculator should you bring and how should you make best use of it during the test? In this guide, we’ll cover everything you need to know about calculators on the ACT, from when you are allowed to use them, to what kinds are allowed, to how to avoid the most common calculator mistakes.

What Section Can I Use a Calculator On?

You may only use a calculator for the ACT math section. Despite the fact that some ACT science questions require basic calculations like addition or division, a calculator is strictly forbidden on every section except for ACT math. 


Do I Need a Calculator?

Technically, you do not need a calculator for the ACT. This is because the ACT is a standardized test and it would be unfair of the makers of the test to discriminate against anyone who could not afford to buy a calculator.

That said, you should definitely bring a calculator! Though you will only ever need to perform basic calculations for the test, it is much less time consuming (and often far more accurate!) to plug $64 * 3.14159$ (or π) into your calculator than it is to solve it long-hand.

If you’re doing every ACT math question by hand, you will most likely NOT complete the full section within the allotted time. So do bring your calculator (as well as an alternate calculator and/or extra batteries).

Always keep this information in mind as you go through the test. A calculator isn't technically needed for the test, so think about how that applies to how you approach each question. If you think you're being asked to find the perimeter of a cube with side lengths of √15 and none of the answers are in root form (i.e., 4√15), chances are you misread or misunderstood the question. Are they actually asking you for the cube's area? Did you calculate the sides of the cube inaccurately?

If you find that there is no way to find an answer to a problem without a calculator (if you need to do something more than basic calculations, which we will discuss later in this guide), you are on the wrong track! Take a step back and reevaluate what you are being asked. 



One of these paths takes you much farther away than you wanted to be. 


Types of Calculators Allowed on the ACT

The ACT is a little more strict than the SAT is when it comes to the calculators you are allowed to bring. For example, the SAT allows the TI-89 (a popular calculator), while the ACT forbids it.

For the ACT, you can bring any calculator that does NOT have computer algebra system (CAS) functionality. A CAS calculator can solve problems algebraically, which would defeat the purpose of many of the ACT questions.

If your calculator is not on the restricted list, it is allowed. According to official ACT guidelines, you must clear: all documents on your calculator (so that you cannot bring notes), all programs with CAS capability, and all apps with CAS capability.They specifically mention that it is not enough to disable these programs--they must be fully removed.

That said, most proctors are not as strict as the ACT guidelines. If you have a restricted calculator or functions, it won't hurt you to try to bring it to the testing center. But do bring a back-up calculator that you're used to using in case your proctor won't let you use your first choice calculator. 

Types of Calculators NOT Allowed on the ACT

This is the forbidden valley list of calculators and devices. Anything NOT on this list is approved by default:

  • You are NOT allowed to bring any kind of laptop, phone, tablet, or PDA to use as a calculator.
  • You CANNOT have anything that plugs in.
  • You CANNOT have anything that makes noise or can communicate with another device.
  • You CANNOT have anything that has a QWERTY keyboard on it.

Texas Instruments:

  • You CANNOT have any model that begins with TI-89
  • You CANNOT have any model that begins with TI-92
  • You CANNOT have the TI-Nspire CAS
    • (The TI-Nspire non CAS is allowed)


  • You CANNOT have the HP Prime
  • You CANNOT have the HP 48GII
  • You CANNOT have any model that begins with HP 40G
  • You CANNOT have any model that begins with HP 49G
  • You CANNOT have any model that begins with HP50G


  • You CANNOT have the fx-CP400 (ClassPad 400)
  • You CANNOT have the ClassPad 300
  • You CANNOT have the ClassPad 330
  • You CANNOT have the Algebra fx 2.0
  • You CANNOT have any model that begins with CFX-9970G


body_abacus.jpgNo official word on whether or not you're allowed to bring an abacus, but my advice is to stick with devices that were designed after 1980. 


What Calculator is Best?

In terms of calculator use for the ACT, familiarity is better than gadgetry. Because you are only going to be asked to perform basic calculations on the ACT math section, you do not need the most high-tech and advanced calculator models that exist in the world. Fancy calculators are more likely to slow you down while you try to figure out their quirks and functions than they are to help you. 

That said, if you are most familiar with a high-tech (and ACT-approved) calculator, definitely bring it! What's most important is that your calculator is one you know well and are used to using. So pick one calculator and use it for everything. Use this same calculator for your math classes as well as on the ACT, so that you can become familiar with it before test day.

If, on the other hand, you have no preference and are looking for advice on a calculator model, my personal favorite for the ACT is the TI-30X. It’s great if you’re on a budget (no matter where you shop, you can get it for less than $18) and will do everything you need--parentheses, negatives, exponents, square roots, four basic functions, etc.--without getting into the overly complex functions and capabilities (which you won’t need anyway).

But no matter what, make sure you familiarize yourself with your calculator before test day! Do some practice problems with your calculator at home before you take your official test.


Don't just reach for the fanciest device you can find--make sure you really know your machine!

How to Avoid Common Calculator Mistakes

Although you should definitely bring a calculator (again, preferably the calculator you feel most comfortable with), it is far more important to understand the question than it is to immediately reach for a calculator.

Many problems are actually much simpler than they appear and can be done in seconds without a calculator. Don’t automatically reach for the calculator before you analyze the problem


With a problem like this, there are several approaches, each taking more or less time than the other. 


Option 1) Fastest way, no calculator. 

The question tells you this is an isosceles triangle. If you remember your formula for isosceles triangles, you can immediately say that the hypotenuse is $\s√2$ or, in this case, $10√2$. So the answer is E


Option 2) Medium-fast, no calculator.

You can quickly see that $10^2 + 10^2 = 200$. The hypotenuse, therefore, is:

$√200$ or $√100 * √2$

This becomes $10√2$. So the answer is E.


Option 3) Slowest way, with calculator.

If you forget both your isosceles triangle formula and how to reduce square roots, you can still do this problem (though it will take longer). 

$10^2 + x^2 = c^2$

You know that this is an isosceles triangle, so each side will be equal:

$10^2 + 10^2 = c^2$

$200 = c^2 => c = √200$

If you do not remember how to reduce the square root of 200, find the answer in your calculator (approximately 14.14) and then find the answer that matches. 

A, B, and C are eliminated, as they are integers. The square root of 20 will be far too small (4.47), since you are trying to find the square root of 200. 

The square root of 2 is 1.414.

$(1.414)(10) = 14.14$. So the answer is E, $10√2$

As with the above, some questions can be solved much faster in your head (or on scratch paper) than on a calculator.

If the question requires a calculation you cannot do quickly or easily in your head, definitely use your calculator. But make sure to always double check your input line (the part where you type into your calculator) before you calculate the results! Plugging in the wrong values (or forgetting that crucial negative sign or parentheses) can make all the difference between a right and a wrong answer.

If you have $x = -5$ and an equation $f(x) = x^2 + 12$, make sure that you are plugging in your x correctly. 

There is a huge difference between plugging in $-(5^2) +12$ and $(-5^2) + 12$ into your calculator! The first equation is inaccurate and gives you -13. The second equation is correct and gives you 37

Make sure you are calculating for x equals -5 here, NOT the finding the negative of 5 squared. 

If you’re making numerous errors in your practice tests, write down the equation by hand first. Even if it’s a problem that looks simple, doing it entirely on a calculator (or in your head) can lead to errors. Write down your steps before you whip out the calculator.


When to Use Your Calculator

You will never need your calculator to more than a few basic calculations. You will only ever be asked to:


(e.g. $213 + 456$)


(e.g. $3500 - 1200$)


(e.g. $33 * 10$)


(e.g. $54/3$)

Take a number to an exponent

Even so, you will only need to express a number to an exponent that is able to be calculated by someone without a calculator. For example, you may need to manipulate $x^23$ or $y^10$, but this is based on your understanding of exponent rules:


Based on your knowledge of how exponents work, you know that $x^a * x^b = x^[a+b]$. 

So we have:

$(2)(3) = 6$

$x^4 * x^5 = x^[4 + 5] = x^9$

$y^1 * y^8 = y^[1 + 8] = y^9$

So the final answer is H, $6x^9y^9$

As you can see, this can all be done without a calculator. The ACT will never ask you for the answer to large exponent values, so you will never need to find the value of $3^23$ or $2^10$, for example.

The ACT math example above is typical of an exponent question you'll see on the test. 

Find the square root of a number

Square root problems will only be as complicated as making you find the value of perfect squares (e.g. $√81$), or having you reduce square roots (e.g. $√18 = 3√2$). If you know your basic squares ($2^2 = 4$, $3^2 = 9$, etc) and if you know how to reduce a square root, then you won’t need a calculator.

Put several of these calculations together.

The hardest part of your calculations will be in keeping them straight and putting them together

body_question_4-1.pngAgain, you can solve this problem in one of two ways--with or without a calculator. 


Option 1) Fastest way, no calculator.

Think about the percentages in terms of solid units of something. In this case, think of them as marbles. If you have four marbles and increase the amount by 25%, you are adding one marble (25% is equal to $1/4$th). 

So now you have five marbles. 

Then, you must take away 20% of those five marbles. Well 20% is $1/5$th, so you are now back to four marbles. 

You began with four marbles and you ended with four marbles; you have exactly what you started out with. 

So the answer is C, 100%


Option 2) Slower way, with calculator.

You could also solve the problem algebraically. 

$x + 0.25x = 1.25x$

$1.25x - (0.2)(1.25x) = 1x$ or 100%

Either way, you are left with answer C, 100%


Bottom line: if you find you are trying to perform more complicated equations than these basic ones, you are likely going down the wrong path! Put your calculator down and examine what the question is really asking.

Don't allow your time and energy to get sucked into doing unneeded calculations.

The Take-Aways

A calculator can be a great asset on the ACT, but only if you know how to use it properly. Make sure first that you are interpreting each problem correctly and develop the correct approach before you reach for your calculator. It’s far more important that you have a solid understanding of the mathematical concepts you’ll be tested on for the ACT than it is for you to be an expert at manipulating your calculator.

Double check that your calculator is ACT-approved, familiarize yourself with your calculator model before test day, and know that if you’re going down the rabbit hole of functions for each question that there is likely a much easier way to solve the problem, and you will be good to go on test day!


What's Next?

Looking to boost your ACT math scores? Make sure you know exactly what's tested on the ACT math. And review your list of ACT math formulas to make sure you know everything you need to before test day!

Looking for an ACT math tutor? Read up on what makes for a good ACT math tutor

Aiming for a perfect score? Look no further than our article on how to get a 36 on the ACT math, written by a 36 ACT-scorer. 


Have friends who also need help with test prep? Share this article!
Courtney Montgomery
About the Author

Courtney scored in the 99th percentile on the SAT in high school and went on to graduate from Stanford University with a degree in Cultural and Social Anthropology. She is passionate about bringing education and the tools to succeed to students from all backgrounds and walks of life, as she believes open education is one of the great societal equalizers. She has years of tutoring experience and writes creative works in her free time.

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