You’re sitting in a quiet room, pencil in hand, heart thumping against your ribs. The proctor starts reading the rules, and suddenly, you realize the expensive piece of plastic on your desk might be illegal. It happens more than you’d think. Prohibited calculators on ACT testing days are a fast track to a voided score and a very long, very quiet walk to the parking lot. It’s not just about "cheating" in the way we usually think about it. It’s about the ACT’s obsession with fairness—and their deep-seated hatred for anything that can solve equations automatically.
Honestly, the rules are a bit of a moving target. You’ve probably seen your friends using high-end TI-Nspires in AP Calculus and figured, "Hey, if it works for a college-level math class, it’s fine for a standardized test, right?" Wrong. Very wrong. The ACT is remarkably picky about what makes a calculator "too smart" for its own good. If your device has a Computer Algebra System (CAS), you're basically toast.
What Actually Counts as Prohibited Calculators on ACT?
Let's cut to the chase. The most common reason students get flagged is the CAS feature. This isn't just a fancy name; it’s a specific type of software that can manipulate symbolic expressions. If your calculator can factor $x^2 + 5x + 6$ into $(x+2)(x+3)$ without you doing any of the heavy lifting, the ACT doesn't want it in the building.
The biggest offenders? The TI-Nspire CAS and the TI-89. These are powerhouse machines. They are amazing for engineering students, but they are strictly forbidden on the ACT. It doesn't matter if you promise not to use the CAS functions. It doesn't matter if you've cleared the memory. The hardware itself is the violation. I've seen students try to argue that their TI-Nspire "isn't the CAS version" because they swapped the keypad. Don't do that. Proctors are trained to look for specific model numbers, and "Nspire CAS" is at the top of their hit list.
Wait, there’s more. It’s not just the Texas Instruments crowd that needs to worry. The HP-40G, HP-48GII, HP-49G, and the HP-50G are all on the "no-fly" list. Same goes for the Casio ClassPad 300 and 330, and the entire PRIZM series if you're using specific models like the fx-CP400. Basically, if it looks like a mini-computer or has a touchscreen, you should probably assume it’s banned until you prove otherwise.
The "Dumb" Features That Still Get You Banned
You might think you’re safe because you have a basic graphing calculator. But the ACT goes deeper into the weeds than just CAS software.
Electronic writing pads. Pen-input devices. Handheld computers. These are all obvious nos. But did you know you can't use a calculator that has a QWERTY keyboard? If it has a full "A through Z" keyboard layout, it's considered a communication device or a data storage tool. That’s why the TI-92 is banned. It looks more like a 90s-era PDA than a calculator. Even if the keys are tiny and rubbery, if they're in that specific QWERTY order, leave it at home.
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And then there's the noise. If your calculator talks—literally—it’s out. If it makes loud clicking noises or has an overhead projector interface (yes, those still exist), it's prohibited. The ACT is a "silent" environment. Anything that disrupts that, or allows you to share your screen with a neighbor, is a massive red flag.
Beyond the Hardware: Software and Mods
Let’s talk about the sneaky stuff. Some kids think they can get around the rules by downloading programs onto a "legal" calculator like a TI-84 Plus. Technically, the ACT allows programs, but there are massive caveats. You cannot have programs that perform CAS-like functions. You can't have programs that have copies of the test questions or large blocks of text stored in them.
The proctors have the right to check your "Apps" and "Programs" folders. If they see a program named "ACT_ANSWERS" or "MATH_FORMULAS_DUMP," you’re going to have a very bad morning. They don't have to prove you used it. Just having it on the device is often enough to get you disqualified.
- Cell phones? Obviously banned. You can't use the calculator app on your iPhone.
- Tablets? Nope. No iPads, no Kindles.
- Laptops? Don't even try it.
- Wearables? This is the big one for 2026. Your Apple Watch or Galaxy Watch is not a calculator. It’s a prohibited device. Many testing centers now require you to put your watch in a plastic bag under your desk.
Why the TI-84 is Still the King (and How to Use It)
There’s a reason why the TI-84 Plus and its various iterations (Silver Edition, CE, etc.) are the gold standard for testing. They are the most powerful devices that are consistently allowed. They hit that sweet spot: they can graph complex functions and handle matrices, but they don't have that pesky CAS software that triggers the ban.
However, even with a TI-84, you aren't totally in the clear. You have to make sure your calculator doesn't have any weird attachments. No "sensor boats" for science experiments. No charging cables plugged into the wall (you must run on battery power). And for the love of everything, make sure your batteries are fresh. I once saw a student’s calculator die during the last five questions of the math section. He cried. I felt for him, but there are no do-overs for poor battery management.
Real Talk: What Happens if You're Caught?
It’s not like a "warning" situation. If a proctor spots one of the prohibited calculators on ACT desks during the math portion, they are instructed to dismiss you immediately. Your test will not be scored. You will not get a refund. Depending on the severity—like if they find you've programmed the formulas into a TI-84 against the rules—you might even be barred from taking the test again for a certain period.
It's a high-stakes gamble for a very low reward. The math section is designed to be solvable with a basic scientific calculator. The fancy graphing functions on an Nspire CAS might save you 10 seconds on a problem, but it’s not worth the 100% risk of losing your entire score.
Making Sure Your Device is Clean
So, what should you do tonight? First, flip your calculator over. Look at the model number. If it says "CAS" anywhere on it, stop. Do not pass go. Go to the store or borrow a friend’s TI-84 or a TI-30XIIS.
If you have a TI-84, check your "Mem" settings. While the ACT doesn't strictly require a full memory wipe like some local school exams do, it’s a "best practice" to clear your RAM. It prevents any weird glitches and ensures there’s nothing on the device that could be misinterpreted as cheating. To do this on a TI-84, press [2nd] [MEM] [7] [1] [2]. It’s a five-second process that gives you total peace of mind.
Also, check your screen brightness. This sounds dumb, but if your screen is so bright it’s reflecting off your glasses or visible to the person three rows over, a proctor might get suspicious. Keep it reasonable.
The Scientific Calculator Alternative
If you're stressed about the rules, just use a scientific calculator. Seriously. A TI-30XIIS costs about $15 and is bulletproof. It can't do CAS. It can't store massive amounts of text. It's 100% legal on every version of the ACT ever printed. Most of the "advanced" features on graphing calculators actually slow you down on the ACT anyway. You spend more time typing in the equation and adjusting the window than you would just solving the algebra by hand.
The ACT math section is a race against the clock. 60 questions in 60 minutes. A "legal" but complex calculator can sometimes be a trap. You get sucked into trying to graph something that could be solved in two steps with a simple ratio.
Actionable Steps for Test Day
Don't let a hardware error ruin months of prep. Follow these steps to ensure you're compliant:
- Check the Official List: Visit the ACT.org website 48 hours before your test. They update the prohibited list occasionally, and 2026 has seen some tighter restrictions on "hybrid" devices that blur the line between calculators and computers.
- Inspect the Exterior: Remove any "cheat sheet" stickers that come inside the plastic covers of some calculators. If your cover has a list of unit conversions or constants, leave the cover in your locker or bag.
- Battery Check: If you use a TI-84 Plus CE (the color one), charge it to 100% the night before. If you use an older TI-84 that takes AAA batteries, put a brand-new set in today. Don't wait for the "Low Battery" warning.
- The "Backup" Strategy: If you're nervous, bring two. You are allowed to have a backup calculator on your desk, provided it's also a permitted model. If your main one glitches or the proctor decides they don't like the look of it, you have a plan B ready to go.
- Remove the Extras: If you have any plug-in modules (like the old TI-84 silver edition ports), take them out. The device should be "stock."
The math section is hard enough without the added stress of a technicality. Keep it simple, keep it legal, and keep your eyes on your own paper. The best calculator in the room is the one between your ears; the one on your desk is just there to handle the decimals.
Prohibited Calculators Summary
To keep it simple, if your calculator is on this list, it's staying in the car:
- Texas Instruments: All model numbers beginning with TI-89 or TI-92, and the TI-Nspire CAS (Note: The TI-Nspire non-CAS is generally okay, but be careful).
- Hewlett-Packard: HP 48GII and all model numbers beginning with HP 40G, 49G, or 50G.
- Casio: ClassPad 300 and 330, fx-CP400, and all models in the ALGEBRA FX 2.0 series.
- Anything with a built-in QWERTY keyboard or touchscreen capabilities.
Double-check your gear now. It’s the easiest part of the test to get right.