A word about date formats

Date formats of contact's event's are another dark chapter in the book of Android development. Google missed it to specify the format in which dates should be stored in the contacts database. This leads to a situation where each device uses a different format. Some devices seem not to care at all which format is entered. Some devices want yyyy-mm-dd in order to show the correct birthday. Other devices use Unix timestamps. As there is no way (at least I could not find any) to determine the used format, CardDAV-Sync has an option to set the format your device uses.

How can you determine the format your device expects?

Currently the only way to determine the format your device wants is by trial & error.
First, create your account read-only and see if your device already shows the correct birthdays. If so, you can disable the One-Way-Sync setting if you like (go to "Edit account settings" to do so).
If not, go to "Settings" -> "Accounts" -> <your CardDAV-Account> -> "Edit account settings" and set the "Enforce synchrony" option.
Then, launch CardDAV-Sync from the launcher menu, set a different date format and delete the CardDAV contacts with a birthday field. CardDAV-Sync will recreate them immediately (since you set One-Way-Sync and "Enforce synchrony") using the new date format. (For large numbers of contacts you may be better off by removing and recreating the whole account.)
Please send me your phone model, OS version (or custom ROM version) and which format works for you, so I can maintain a list with devices and which format works (see below).

Many devices will work out of the box with the default format "yyyy-mm-dd". Please contact me if none of the three formats work for you.

The entries in the following list are reported by users to give you a hint which format may work for you. Please use it with care, as not all entries may be correct.

IndexManufacturerModelOS version/custom ROMFormat
1AcerLiquid S100Android 2.3.7, Custom Mod LiquidNextyyyymmdd
3HTCOne XAndorid 4yyyy-mm-dd
4MotorolaDefy2.1-update1 with Motoblurtimestamp
6Samsungall modelsall versionsyyyy-mm-dd
7Sonyxperia x102.1yyyy-mm-dd