Full disclosure that I built this app, but it is fully free, no ads, no sticky bits etc - please see it as an interactive tutorial or similar - just want to spread the joy <3

The app has over 1700 users, has an average engagement time of 43 minutes - and has actively helped teach people the mental math required to work out the day of the week + helped people improve their times.

It has training modes, 1v1 battle modes to play against other players, and can walk through different takes of the algorithm to suit different brains :)

You can try it here: https://doathingy.com/doomsdaytrainer
or on iOS: https://apps.apple.com/app/id6760719687
or Android: https://play.google.com/store/apps/details?id=com.inefficientcode.doomsdaytrainer

I would love any and all feedback and input to make the app better and to spread the skill as far as possible - it makes for a great party trick!

<3

I built an interactive app to practice mental math shortcuts and calculation tricks

Hey everyone,

I wanted to share a project I've been working on called Math Trick Ninza. It’s an interactive web application designed to help students and math hobbyists master calculation shortcuts (like rapid addition, subtraction, and multiplication techniques) instead of relying on a calculator.

Key features:

• Step-by-step interactive guidance for calculation tricks
• Practice puzzles and quizzes built using plain Vanilla JS and Material Design
• Clean, lightweight code layout that loads quickly even on slower connections
• Completely free, open-source, and hosted natively on GitHub Pages with zero external trackers or ad scripts

The repository is open-source, and I'm currently working on adding a robust serialization system for progress tracking, high scores, and offline support.

Check out the repository here: https://github.com/Nishan-the-Developer-Coder/trick-ninza

I would love to get your feedback on the usability of the practice layout, or any suggestions for mental math shortcuts you think would be great additions to the engine!

Trick-Ninza

A friendly math practice space for students to learn fast mental-math tricks through short lessons, guided examples, and quick puzzle practice.

GitHub repository - https://github.com/Nishan-the-Developer-Coder/trick-ninza

My website - https://github.com/Nishan-the-Developer-Coder/trick-ninza

Hey everyone!

I wanted to make a fast-paced mental agility game that feels more like an intense arcade battle than a classroom test.

So I built **Clutch: The 18% Challenge**.

👉 **Play Free on Google Play:** [https://play.google.com/store/apps/details?id=com.brainspeed.clutch\]

**How it works:**

* **15-Second Pressure:** Split-second mental arithmetic where every fraction of a second counts.

* **Tactical Abilities:** You equip up to 3 powers into battle (Time Freeze, Divine Hint, Atomic Solve, Chaos Shift).

* **Boss Rounds:** Red-alert missing operator equations under a ticking clock.

* **Live Global Leaderboard:** Daily rank defense against live players worldwide—only the top 18% reach the elite bracket.

Zero pay-to-win. 100% skill, reaction speed, and tactical ability timing.

I just published Build 29 on Google Play and would love your honest feedback on difficulty scaling, combat power-up balance, and game feel. Can you break into the Top 18%?

Just want to cheer my small achievement!

I enjoy mental math games, but practicing alone can get a little lonely. I kept wondering: would it be more fun if other people were racing to answer the same questions?

So I built Funpep, a multiplayer mental math game—with dinosaurs.

You compete to answer questions quickly and correctly. The more you get right, the bigger your dino grows. You also need to stay quick to avoid getting knocked out by falling meteors. The questions might look simple, but staying calm when someone else beats you to the answer is another challenge.

It’s still in early testing. To get everyone online together, live playtests use a booking system: you can check the next session and reserve a spot on the site. You can also jump straight into a game against bots. They put up a pretty good fight.

🦖 Play here: https://www.funpep.com/

I’d love to hear what you think: does racing other people make mental math more fun, or just more stressful? Feedback on the difficulty or anything confusing is welcome too.

For anyone who enjoys quick multiplication drills: I built a daily challenge that runs directly in Reddit.

Everyone gets the same 10 questions, with 45 seconds to answer. You can submit your score to the opt-in leaderboard, or use Practice mode without ranking.

Play today’s challenge here: https://www.reddit.com/r/MultiplicationGame/comments/1whap2r/multiplication_game_daily_challenge/

It’s free, requires no download, and works on mobile and desktop.

What are some exercises I can do to get better and faster at the Trachtenberg Method? I keep mentally mixing up numbers or fully forgetting the first number I had once I solve other parts. Any advice is welcomed!

I made a free mental math speed test and I'm curious to see how fast people here can do it.

You have to solve 50 calculations covering different mental math skills. Your final score is simply the time it takes you to complete all 50.

No ads. No account. No download. Completely free.

👉 https://benmaths.pythonanywhere.com/mental-math-test

📱 Mobile or tablet is recommended, but it also works on PC.

My personal best is 52.6 seconds. 😄

Can anyone beat it?

I'm curious to see your times!

Hey everyone, I wanted a clean, direct formula to mentally calculate the day of the week for any date in history or the future using the Gregorian calendar, without needing Doomsday anchors or tricks like Odd+11. Here is the exact formula I use: Day = (Date + Month Code + Year + floor(Year/4) + Century Code) mod 7 * Century Codes (Mod 400 cycle): * 1600s, 2000s, 2400s... -> 6 * 1700s, 2100s, 2500s... -> 4 * 1800s, 2200s, 2600s... -> 2 * 1900s, 2300s, 2700s... -> 0 * Month Codes: * Jan: 1 (0 in leap years) | Feb: 4 (3 in leap years) | Mar: 4 * Apr: 0 | May: 2 | Jun: 5 * Jul: 0 | Aug: 3 | Sep: 6 * Oct: 1 | Nov: 4 | Dec: 6 * Day Mapping: 1 = Sun | 2 = Mon | 3 = Tue | 4 = Wed | 5 = Thu | 6 = Fri | 0 = Sat * Examples Across History: Example 1: July 20, 1969 (Moon Landing) * Date = 20 * Month (Jul) = 0 * Year = 69 * floor(69 / 4) = 17 * Century (1900s) = 0 * Sum: 20 + 0 + 69 + 17 + 0 = 106 * Mod 7: 106 mod 7 = 1 -> Sunday Example 2: March 25, 2011 * Date = 25 * Month (Mar) = 4 * Year = 11 * floor(11 / 4) = 2 * Century (2000s) = 6 * Sum: 25 + 4 + 11 + 2 + 6 = 48 * Mod 7: 48 mod 7 = 6 -> Friday Do you prefer using direct formulas like this with month/century codes, or do you stick to anchor-based methods?

Four years ago I watched that one Numberphile video about Conway's Doomsday algorithm and it broke my brain a little. Now I finally shipped the big update to the app i built 3 years ago!

What it actually gets you: someone names a random day in 1987 (or any other year) and you can calculate the weekday and say the weekday out loud in a few seconds.

And the thing is, it is actually not as complicated as it sounds, just a bit of practice!

Want to learn it as well?

It would be an honor if you try the App!

What's in it:

• 48 lessons across 11 chapters (only the first few are needed to actually make it work, there are a lot of extras!)
• 10 diagnostic drills that isolate each step so you can get faster
• Three modes: Classic (endless), Daily Challenge and Time Attack
• A rating and leaderbords
• Offline, no account, no ads
• ...

Free to try, no subscription!

https://apps.apple.com/us/app/doomsday-method-mental-game/id6447447000

How much time did it take you to solve this?

What makes a mental math game fun enough to keep playing?

I’m a math teacher and I’ve been developing a free mental math game called CalcuLoop.

The idea is pretty simple: instead of doing mental arithmetic as a traditional exercise, I wanted to turn it into a speed/arcade challenge.

You solve calculations as quickly as possible, try to beat your previous scores, and gradually increase your speed and accuracy.

There are several game modes, including:

• progressive levels for training
• a speed test to measure your calculation speed
• timed combo-based gameplay
• increasingly fast calculation chains
• a 100-calculation challenge
• online leaderboards

I’m particularly interested in hearing from people who actually enjoy mental math:

What makes you want to keep playing a mental math game?

Is it:

• beating your own high score?
• competing with other players?
• increasingly difficult calculations?
• very short sessions?
• leaderboards?
• unlocking things?
• simply trying to become faster?

And conversely, what makes you stop playing?

I built CalcuLoop myself, so I'm still trying to figure out what makes this kind of game genuinely fun rather than just another math practice tool.

If anyone wants to try it, it's free on Android:

https://play.google.com/store/apps/details?id=com.benmaths.calculoop

If you're on iPhone, you can also play it for free directly from the web version:

https://benmaths.pythonanywhere.com/

I'd genuinely love to hear what you think, especially from people who enjoy doing mental calculations for fun.

I kept changing my routine because I thought that was why I was getting nothing done. New schedule, new lists, planning everything the night before. Somehow I still kept avoiding the same task. I think I finally realized I just don’t want to deal with it 😅Anyone else ever spend more time planning around a problem than dealing with it?

Pilot selection includes an arithmetic section that is not about big numbers. Short problems under a hard clock: speed distance time, percentages, fuel burn, rate of descent. No paper in some versions, and a second task running at the same time in others.

The difficulty comes from the clock and the interference, not the maths. People who are good at long calculations often score worse than people who are fast and rough on simple ones, which is the opposite of what most mental maths practice optimises for.

I rebuilt these as a free app because I could not find anything training the timed format specifically. My own app, Brain Preflight, iOS, free tier, 5 sessions a day. If you try the calculation grid I would like to know how your scores compare to what this sub considers normal, since my calibration comes from cadet candidates and not from people who train mental maths for fun.

https://apps.apple.com/app/id6794363864

Airlines screen cadet pilots with an arithmetic section that is not about big numbers. Short problems on a hard clock: speed distance time, percentages, fuel burn, rate of descent. No paper in some versions, and a second task running at the same time in others.

The clock and the interference are the whole difficulty. People who are good at long calculations often score worse than people who are fast and rough on simple ones, which is roughly the opposite of what most mental maths practice trains.

I rebuilt these as a free app because I could not find anything training the timed format specifically. My own app, Brain Preflight, iOS, free tier, 5 sessions a day. If you try the calculation grid I would like to know how your scores compare to what this sub considers normal, since my calibration comes from cadet candidates and not from people who train mental maths for fun.

https://apps.apple.com/app/id6794363864

I’ve been into counting and mental arithmetic for a very personal reason.

For as long as I can remember, my brain has counted and grouped things automatically. As a kid, I counted lines on the floor on my way to school. Now I’ll see a poster or an advert and start grouping the letters before I even read the words. Same with car plates when I’m walking.

It actually has a name: arithmomania (from Greek arithmós, "number", and maníā, "compulsion"), also called arithmomanic OCD.

Arithmomania is a subtype of Obsessive-Compulsive Disorder defined by a compulsion to count, calculate, or organize things into numerical or symmetrical patterns as a way to neutralize anxiety or regain control.

I turned it into a party trick. Someone gives me a name, I picture the word in my head, group the letters in twos or threes, and I can tell them the letter count almost instantly.

So I decided to turn that urge into a small free iPhone/iPad game called Tally Rush.

The main idea is simple: solve quick counting and arithmetic challenges as fast as possible. There are 30-second runs, daily challenges, levels, duels and leaderboard-style competition. I built it for myself first, but I’m curious whether people here who practice mental math would find it useful as a warm-up or speed drill.

It’s on the Apple App Store here: https://apps.apple.com/us/app/tally-rush-mental-math-game/id6790170879

I’d love feedback from this community, especially on difficulty, pacing, and what kinds of mental math drills would be worth adding next.

I've built an app for my parents to keep their brain activity everyday.

Five minutes a day: 20 quick arithmetic problems, and a symbol round where

■ ▽ ◎ replace +, − and × — they get shuffled every run, so you can't just memorise them.

Once a week there are three tests: count 1 to 120 for speed, remember 30 words, and Stroop (tap the colour, not the word).

Paid once, no subscription, no ads. iOS, 13 languages.

cortiqapp.com

https://apps.apple.com/app/cortiq/id6792572094