A surprise party with friends and family or a themed party are two 40th birthday party ideas. While some may not like the idea of a surprise party, it is a way to get everyone together to celebrate the birthday milestone. Some ideas for a themed party might be favorite sports team, historical era or movie genre.
To plan the surprise party, first sit down and make a list of everyone to invite. Be sure to explain that the party is a secret so the party remains a surprise. If the party is at a house, find a place to park all the cars as those are sure to ruin the surprise element. To make it even more of a surprise, plan the party a few days before the actual date.
A themed birthday party is another way to get guests involved in the celebration. Since 40 is not quite over the hill, think instead of having a theme consistent with a favorite sport or sports team such as football or bowling. Plan some easy outdoor games to go along with the sports theme. History buffs might enjoy a Roaring '20s or Disco '70s theme, while movie aficionados may find a horror or classic comedy theme enjoyable.