Hi I started to write a little utility to generate bills. And I need to know the number of days in a month and I was surprised that (Month month: 2) daysInMonth returns 28 because we do not know :) So I thought that I was obviously wrong and I should use (Year year: 2016) daysInMonth > "#(31 28 31 30 31 30 31 31 30 31 30 31)" :( When I look at the implementation this is clear that it is wrong daysInMonths ^ Date daysInMonth totally not aware of the year. I think that daysInMonths should use DateAndTime creating a dummy date for each month and using asMonth daysInMonth (DateAndTime year: 2016 month: 2 day: 3) asMonth daysInMonth > 29 Year >> daysInMonth: aMonthNumber "Returns the days in month for a given month" <expr: #(#(#Year #year: 2016) #daysInMonth: 2) result: 29> ^ (DateAndTime year: self year month: aMonthNumber) asMonth daysInMonth I extended the class with some more practical methods. What do you think? I should push them to pharo? I was surprised that the library was not that good. Stef