Knowing 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're allowed to use them, to what kinds are allowed, to how to avoid the most common ACT calculator mistakes.
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.
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'll only ever need to perform basic calculations for the test, it's 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. 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? Or 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 (basically, 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're being asked.
One of these paths takes you much farther away than you wanted to be.
The ACT is a little more strict than the SAT is when it comes to the calculators you're 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's 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 aren't as strict as the ACT guidelines are. 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.
This is the forbidden valley list of calculators and devices. Anything NOT on this list is considered an ACT-approved calculator by default:
No 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.
In terms of calculator use for the ACT, familiarity is better than gadgetry. Because you're only going to be asked to perform basic calculations on the ACT math section, you won't need the most high-tech and advanced calculator model 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, I'd personally recommend the TI-30X as the best calculator for ACT Math. The TI-30X 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!
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. So 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:
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).
You know that this is an isosceles triangle, so each side will be equal:
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.
For example, if you have $x=−5$ and an equation $f(x)=x^2+12$, make sure that you're 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.
You will never need your calculator to do more than a few basic calculations. You will only ever be asked to:
