Adding more guests?!

Check with your venue. Some venues add on an extra charge per person past 100 for chairs.

Any area where you are paying per guest would go up - like you said, food, drink, and favors. Also if you are paying for tables, chairs or linens, you'll need more. If you're trying to keep cost down, remember that favors are optional and your guests will likely not miss them if you skip them.

It depends on what is included in your contract- tables, chairs, linens, centerpieces, candles would be a few.

Linens, centerpieces. Food will likely be charged with tips and tax, so include that, but parking, restroom attendants, etc may have points where you get charged more per person.

Don't forget vendors (band or DJ, photog, etc) and you and groom in head count. Some places count vendors separately. Unless you are already giving every single guest a plus one, allow for people to get engaged between now and your wedding.

I second Criz: chairs, linens, sometimes a separate charge for china, bigger cake (I forgot about that one), chairs for ceremony too, centerpieces, more programs, more escort cards, more invitations ( I was happy we got super fancy invitations because we didn't need many ), programs. Also keep in mind, more people=longer to get seated at ceremony and reception, longer buffet/drink/appetizer lines, harder to pass appetizers, more parking, etc.

Chairs and tables bc you have more people to seat. More liquor to provide

I think its different depending on what your venue will cover so you'll have to ask but we went from 200 to 240.. (yay.... thanks in laws *eye roll*) its $10 extra per person for my venue. that covers chairs. tables & linens. Then I had to factor in what doesn't come with the venue, napkins, charger plates, extra centerpieces for the extra tables, extra votives for the extra tables, along with table numbers, extra menu cards for the place settings, extra STD's & invites, extra guest favors, extra dessert, extra drinks, extra food, not a cost but like they said above, the time frame of things will take a lot longer the more people you have, as well as your time if you are planning to go around to each table and say hi to all your guests.. - I'm a tad bitter if you can't tell

I agree with all of the pp!!!! Is your venue all inclusive, so they cover things like chairs, Chiba, linen, etc? My venue doesn't even charge a cake cutting fee.

Thank you everyone. Our venue does not charge extra for more people and it includes the tables, chairs, decorations, and linens. You all reminded me of some things I hadn't thought of. MrsDamico: we're getting married on the same day!!