Since recently I did not yet had a birthday calendar in my apartment. This was because I namely dislike the very ordinary “toilet kind” of birthday calendars, see below on the left. More than a year ago I stumbled upon a very original birthday calendar on Pinterest. Immediately I became spontaneous, it has a very nice look, it is original with its clothespins and easy to maintain as well as built.
A while ago I finally gave myself the time to replicate the idea. Using the clothespins I determined what the minimum size of the wooden plank had to be, 125 [cm] in length and 25 [cm] in width. At first I tried to find an old plank of a pallet. Those often have that old look which I wanted to go for. Unfortunately none of them did met the requirements w.r.t. the size. So in the end I just bought a plank from a hardware store and sawn it to the correct dimensions.
To do the writing of the header “birthday”, the months and the names of the people I bought a white and black acrylic marker called “DECO painter matt” of the brand Marabu. To make sure that the letters on the wood of the word “birthday” would be consistent, I made a small mold out of paper. The months I just drawn out of hand, same for the names and days on the clothespins.
In the example on Pinterest the clothespins are colored. This can be achieved by coloring the clothespins with paint or by buying colored clothespins. You can find the latter by searching on children toys. I did not color them and searched for old and worn clothespins. If you do not have those you can buy new ones and put them in the watery garden and wait a week or two.
Differerent result found on Pinterest 
Differerent result found on Pinterest