The Handy Calendar

What day of the week is it? For calendar calculating like savant syndrome.

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Handy Calendar


Handy Calendar
iPhone / iPad
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Using diagrams and tests, you can easily learn how to calculate the day of the week for any date in the past or future using the amazing "finger calendar." This app contains 5 lessons beginners to the finger calendar technique. (Each lesson is unlocked in sequence.)


  • Lesson 1 After "n"
  • Lesson 2 Position of each month
  • Lesson 3 The process
  • Lesson 4 Test
  • Lesson 5 Zeller’s congruence


  • Dominant hand compatibility

The finger calendar can be used with either hand, but not both. The app provides diagrams for both right and left hands. (Select dominant hand in Settings.)

  • 3 Tests

3 tests for measuring the user's proficiency.

  • Simulation function

You can simulate the procedure of the finger calendar for the questions with wrong answers on the tests, and actually view how the algorithm works.

  • Intuitive diagrams

Abstracted diagrams allow for intuitive understanding.

  • Originality

The finger calendar technique learned in this app is an original creation by the author based on improvements made to a technique found in folklore.

  • Teaching material for mathematics

This technique is based on elements of adding natural numbers, greater than and less than relationships, and algorithms, and is suitable to be used as a teaching material in mathematics.

Creator’s Comment

I began developing this app around fall 2012. It took about eight months to finish. I had had the idea for some time before that, but there were various technical and development hurdles I needed to think through first, so I released other projects in the interim. From a development point of view, the computational method used herein is the unique creation of an individual, and still largely unknown to the world, so it required special consideration to implement it properly. One advantage to this deliberate approach to development is that it allowed me to further prove and define the validity of this counting method and refine it into something even more simple and intuitive. Another plus was translating the idea into several languages, even though it was considerably challenging! One of the translators later pointed out a mistake in the English original, which necessitated further adjustments. I am extremely grateful for that error being brought to light at an early stage.


Q: What special knowledge do I need to use this?
You shouldn't need any specialized knowledge. The basics come down to addition with integers and thinking about value relationships between numbers. However, some of the text deals with variables (M, D, Y, etc.), so you should have at least a seventh grade understanding of those concepts.
Q: Where did this computational method come from?
The creator modified an existing method that had existed for some time.
Q: Does this method really work?
There's an easy answer to that: please see the documentation in the following section.

Updated: 2018-01-03



- The function to simulate the finger calendar has been added.

- Some errors have been fixed.


Due to a change in the finger calendar procedure, the contents have been updated. (Localization: the app has been released in Japanese and English only. Apologies for any inconvenience.)


Compatible with iOS 8.1.

Portuguese has been added.

Portuguese (Brazil) has been deleted.

Errors where a portion of text could not be displayed in the vertical orientation mode (portrait) have been fixed.


Correspond to iOS 7.



If you have question or request about this App, please contact me from the following page.