Knowunity or Astra AI? Pick Astra AI if your problem is maths, physics or chemistry: it is built around a tutor that solves and explains problems step by step, with lessons aligned to your country's curriculum and graded oral and written mock exams. Pick Knowunity if you want the cheaper all-rounder: over a million notes shared by students, an AI tutor, flashcards and quizzes from your material, and Pro at $49.99 a year against Astra AI Plus at $119.99.
A disclosure first: we make Synt, a third option that we describe at the end, so this is not a neutral review. We only state what we checked and say plainly where each app is better. Every price and feature below comes from the official US App Store listings and the two companies' websites, checked on 31 October 2026.
The short answer
Astra AI (US App Store, 4.8 stars from about 5,300 ratings) describes itself as an AI tutor for maths, physics, chemistry "and beyond". Its listing names a Solver mode (snap a photo of an assignment and get a step-by-step solution), a Socratic mode, lessons aligned to your country's official curriculum, and Exam Prep: take a photo of your exam or pick topics to get a personalised study plan. Its website goes further: add your notes, slides, past papers, exam date and target grade, and it builds a topic-by-topic plan with guided lessons, flashcards, quizzes, a topic podcast, and graded oral and written mock exams.
Knowunity (US App Store, 4.7 stars from about 10,600 ratings) is a study platform with an AI tutor (voice mode and photo homework help), flashcards, quizzes and summaries from your own material, AI-scored mock exams in SAT and AP format, a day-by-day exam plan that fits around your class timetable, over 1 million shared notes, and XP with weekly leagues.
Comparison table
| Knowunity | Astra AI | |
|---|---|---|
| Built around | Exam plan, AI tutor, shared notes | AI tutor and exam prep, strongest in STEM |
| Step-by-step help from a photo | Yes | Yes (Solver mode) |
| Plan to a test date from your material | Yes, day by day, around your class timetable | Yes: notes, slides, past papers, exam date and target grade |
| Flashcards and quizzes from your material | Yes | Yes |
| Mock exams | AI-scored, SAT and AP format | Graded oral and written mock exams (website) |
| Curriculum-aligned lessons | Not described | Yes, by country |
| Shared content from other students | 1M+ notes, summaries and past-paper solutions | Not described |
| Game elements | XP and weekly leagues | Streaks, badges, brain games (website) |
| App languages (App Store) | 20 | 38 |
| Paid plan (US) | Knowunity Pro: $49.99 a year on the website; in-app also $9.99 and $15.99 | Astra AI Plus: $8 a week, $24 a month or $119.99 a year; Astra AI Sigma: $80 a month |
Sources: the Knowunity and Astra AI US App Store listings (description and in-app purchases), the Knowunity Pro page and the Astra AI website. Prices change by country and over time: check inside the app before paying.
What each one costs
Knowunity Pro is $49.99 a year on the US website, which also shows monthly and weekly options; the US App Store lists $9.99, $15.99 and $49.99. The free plan keeps the shared notes in full and limits AI answers, study plans, AI scans and attachments; test grading is Pro only.
Astra AI Plus is listed in the US App Store at $8 a week, $24 a month or $119.99 a year, and there is a higher tier, Astra AI Sigma, at $80 a month, plus credit packs from $15. The website lets you start free. On the yearly plan, Astra AI costs about 2.4 times Knowunity Pro.
Where Astra AI is better
Maths and science problems. Solver mode for the homework in front of you, Socratic mode when you want to work it out yourself, and lessons that follow your country's curriculum. If you are stuck on algebra, forces or chemical reactions, this is what Astra AI is built for.
Exam rehearsal. The website describes oral mock exams you answer out loud and timed written mock exams, both graded. Knowunity's mock exams are SAT and AP format, which matters less outside the US.
Languages. 38 languages in the App Store listing, against 20 for Knowunity.
Where Knowunity is better
Price. $49.99 a year against $119.99 for Astra AI Plus in the US.
Material you don't have. Over a million notes, summaries and past-paper solutions shared by students. Astra AI works from your material and its own lessons.
US exams. Its listing says the day-by-day plan uses the official SAT, ACT and AP guidelines, and the mock exams follow SAT and AP format.
A third option: Synt
This is ours. Synt does one part of what both apps do: it takes your notes (pasted text, a link or photos of your pages) and generates a summary, a quiz, flashcards and a concept map from that material only. Set your exam date and target grade, and it plans short sessions up to that day, re-asks only the questions you got wrong (reworded), and puts a mock exam the day before.
On the web, the free plan covers pasted text, links and photos, including the study plan. PDF upload and YouTube videos are Pro, at €4.99 a week, €9.99 a month or €29.99 a year on synt.app's pricing page, with a 3-day trial; App Store prices are set per country.
Where Synt is weaker: no tutor and no step-by-step solutions, no shared notes, no curriculum lessons, no oral exams. If you need a maths exercise explained, Astra AI or Knowunity will do it and Synt won't. You can try the notes to quiz tool without an account, or build a practice test from your notes.
How to choose
You are stuck on maths, physics or chemistry: Astra AI.
You want shared notes and the lower price: Knowunity.
You are preparing SAT, ACT or AP in the US: Knowunity's plan uses the official SAT, ACT and AP guidelines, and its mock exams follow SAT and AP format.
You have your own notes and an exam date, and don't need a tutor: Synt turns them into a quiz, flashcards and a plan up to the day.
If flashcards are your main method, see Knowunity vs Gizmo; for five more options, Knowunity alternatives.
Knowunity vs Astra AI: FAQ
Is Astra AI better than Knowunity?
For step-by-step help with maths and science, and for graded oral and written mock exams, Astra AI does more. For shared notes from other students, US exam formats and price, Knowunity is ahead. Both now build a study plan to your exam date.
How much does Astra AI cost?
In the US App Store, Astra AI Plus is $8 a week, $24 a month or $119.99 a year, and Astra AI Sigma is $80 a month (checked 31 October 2026). You can start for free.
How much is Knowunity Pro?
Knowunity Pro costs $49.99 a year on the US website (checked 31 October 2026). The US App Store also lists $9.99 and $15.99 options. The core tools are free.
Is there a free alternative to both?
The free plans of Knowunity and Astra AI let you try their tutors with limits. If what you need is a quiz, flashcards and a study plan from your own notes, Synt's free web plan covers that from pasted text, links and photos.
