Typically bakeries suggest that you order a wedding cake from them 6 months in advance, but if it’s past that date for you don’t worry. There are a ton of bakers out there that can do an amazing job for you and will be available with less than 3 months’ notice.
Most of those in the know like to encourage brides to plan on one serving per guest, but if you’re looking to cut your costs you can drop that number down to 20 or so less since not everybody will eat cake, especially if you’re having other types of desserts. But otherwise, I would definitely plan on 1 serving per 1 guest. (NOTE: Groom’s cake should be smaller and only plan to serve about half of the wedding guests with it). Here’s a helpful chart that illustrates how many servings wedding cakes typically have per tier:
So what if you don’t know your final guest count yet? Like catering companies and rental companies, they often don’t ask for your final guest count until a week or two before your wedding. However with wedding cakes it can be a bit different, so talk to you baker about how they want to estimate this. But if we’re going by the general rule of thumb that 20% of your wedding guests will RSVP ‘No’, than planning to order enough cake for 120-130 people (rather than 150) will help your estimate AND your budget.