On average, parents spend roughly $400 on a birthday party they hold at home for about 15 kids. This number covers basic decorations like downloadable invitations, favors, some simple food options, the cake, and activities. But if you decide to get a few menu items catered, hire entertainment, go with an elaborate custom cake, or all of the above, the price can easily reach $600, $800, or more. Also, the more people you plan to invite, the more you’ll spend.