I was in a homewares store, and saw a calendar which works for any day/month/year from now until.. well... until forever, I guess! It looked like this:

http://www.2shopper.com/Cubes_Perpetual_Calendar_p/mma89169.htm

It's a nice idea, but it was rather bulky and used more tiles to indicate the day than necessary. Most designs use 31 tiles, to represent the 31 days of the (longest) month. But, a distant memory of a Martin Gardner column, reminded me that only 12 are actually needed.

So I built this...

(ok - it's my first attempt, and I'm not that handy with card, but I hope this explains the method)

You will need:

Two blank dice
One piece of card
Some clear tape

Step 1: Create a Template

Start by measuring the dice that you will use. The floor on which they sit, and the back, need to fit both dice snuggly. These are shown in the centre of the image, with the triangular lugs either side. Below that is a thin rectangle which will hold the month name. In my version this is 5mm high, which matches the size of the triangle above it.

You will also notice that many of the other sides need to have equivalent lines.

Step 2: Fold It Up

Score along the lines, and fold into the shape above.

Note that the bottom two parts are not scored.

Step 3: Tape It Up

I laid a long piece of tape along the floor and back, along the triangular parts, and stuck it down on each edge. You could also add lugs of the triangular hypotenuses if you prefer to glue it.

Also place a strip of tape on the front of the base, underneath the dice. This is were the month goes.

Step 4: Write on It

On one die write the numbers : 0,1, 2, 3, 4, 5
On the other die write, 0, 1, 2, 6, 7, 8

Write the '6' in such a way that it can be made to look like a '9'! This is the trick in only needing 12 digits. Do this will a sharpie or similar permanent ink.

Write the date along the tape, in dry erase marker.

Each day it is then a simple matter of rotating the dice in the correct orientation to describe the date, and re-writing the month on the 1st.