Desmos is built into digital ACT Math, and you may still bring an approved calculator. One does not replace the other. What Desmos covers is in Desmos on the ACT. What you are allowed to carry is in the calculator policy.
Why bring one anyway
A calculator you already know is faster for arithmetic you trust, and it is your backup if you fumble the on-screen keypad. It has to be a permitted model: no CAS that the policy bans, no phone, no QWERTY keyboard. Practice with the same device you will hold on test day.
Scratch paper is separate. The center provides it. That is in scratch paper on the digital ACT.
Paper testing has no built-in Desmos
If you test on paper, the handheld calculator is the only one. Format choice is in digital or paper ACT.
The bottom line
Bring a familiar, approved calculator even when Desmos is on the screen. Know which jobs you will give to each.
Start practicing
Start with a free diagnostic, then drill your weak spots with 15-question quizzes and track how you're doing across Reading, English, and Math. Compare plans whenever you're ready to go further.
This article offers general ACT prep guidance. The ACT can change from year to year, including its format, scoring, policies, test dates, and fees, so always confirm the latest details on the official ACT website at act.org before you make decisions. ACT® is a registered trademark of ACT, Inc. thirty-six is not affiliated with, endorsed by, or sponsored by ACT.