We invited 140 and we are going to have 70 - so you are probably safe with planning for 50% for a DW. BUT, we are also paying for the whole thing, so when my Dad asked to invite his cousins, I said, "well, then we will have to invite mom's cousins and my FI's parents cousins and we really hadn't planned on adding that many additional people". My Dad forgot that whatever he added, we had to do the same for my FI's side - that may help you FIML understand.