I'm not sure.. I think it's best to be over-cautious than under - worst case scenario, you have too much money and then you can either do extra things/splurge on a nice dinner while away, or come home with extra money left over! Win win!
I've done a fair bit of travelling, but it was always backpacking really, without much of a solid plan, and I tended to go budget budget (as in dorm rooms and supermarket food) and just travel until I ran out of money. I'm not convinced I know how to budget for a proper holiday!