Issue with pickaday in custom thread field

[RateU]

Then you need to modify the value before it is saved into database. Use Input Formatter setting.
You can use strtotime function.

Note that strtotime will assume any xx/yy/zzzz as mm/dd/yyyy format, and xx-yy-zzzz as dd-mm-yyyy format.
http://php.net/manual/en/function.strtotime.php