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One of my previous jobs was coding software for banks that handles financial transactions. And I am not entirely sure any more if it was Feb 30th or 31st but one day the product manager came to my office and asked me to change the validation routine in the library that handles the date-related calculations and consider Feb 31st as a valid date.

Can't exactly remember what it was about but I think some banks or other banking applications are acting like there is a 31st or 30th February for some kind of calculation. (Rather off-topic but if I ever 'share' this with the whole world, it seemed like now is the time!)




When I wrote billing systems for telecoms, Feb 31st was a valid date... after a fashion. Billing cycles were stored as a cycle period "monthly", "quarterly", etc, with a "bill day" offset which was a number 1-31. If your "bill day" was the 31st then in February you would be billed on the last day of the month along with the customers with bill days 28-30. It was rare to do actual time calculations treating the bill day as an actual date, but not considered particularly strange.

And there you have it, at least for one small corner of the software world.


Different markets have different day count conventions. For instance is a 3 month deposit rate the same as a 90 day CD? When it comes to 'wholesale size', it's not about gouging clients for a day of interest, it's making sure that everyone is talking about the same dates and penny-accurate amounts.

http://en.wikipedia.org/wiki/Day_count_convention


My guess is to generate interest for a "month" compounding daily. Bank didn't want to get cheated by February.




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