I use the ddwrt:FormatDateTime function to format the output like yyyyMMdd. inputs like 01/01/2010 work fine but when the day gets over the number 12 the output is an emtpy string. ddwrt:FormatDate(string(@myDate), 1033, 'yyyyMMdd') At first I thought it could be a language specific problem but even none of those combinations work: 13/01/2010 01/13/2010 13.01.2010