About this app

CAN YOU NAME THE WEEKDAY OF ANY DATE? OtterDay turns calendar calculation into a fast, satisfying logic game. Just as location-guessing games make geography feel playable, OtterDay does the same for dates. Learn a reliable mental method, practice it step by step, and work toward finding the weekday in five seconds—without checking a calendar. A SMART WORKOUT FOR YOUR BRAIN Every round challenges your logic, memory, number sense, and mental math. Short sessions keep your mind active while you build a practical skill that feels like a superpower: becoming a human calendar. LEARN, PRACTICE, MASTER Futuristic otter guides teach you the method one piece at a time. Start with recent dates, unlock wider ranges across centuries, and train until the calculation becomes second nature. WHY YOU'LL KEEP PLAYING • Guided lessons that explain the calendar method • Written and spoken-date challenges • Speed and precision training • Progress tracking and personal statistics • Achievements for accuracy, endurance, and fast answers • Flexible difficulty for quick practice or serious mastery MADE FOR CURIOUS MINDS OtterDay is designed for people who enjoy Sudoku, logic puzzles, mental math, number games, brain training, and learning clever systems. The method is related to John Conway's Doomsday Algorithm, presented as a focused puzzle adventure rather than a dry lesson. Keep your mind active. Sharpen your logic. Master the calendar—and see how close you can get to five seconds.