In my experience, here are the things that can cause the most heartache after you get your final bill.
1. Not including tips and gratuity. Tipping on catering alone is often $1500+ so not including it in your budget will cause you a major meltdown later on. Here’s a great tipping cheat sheet I recommend to my couples: http://www.bridalguide.com/blogs/the-budget-guru/how-to-tip-wedding-vendors
2. Not budgeting for overages/accidentals. You always want to provide a cushion in case an unforeseen cost should arise (and it usually does). Examples? the venue only has 1 bathroom so you need to rent a port-a-potty, the tent will need staging due to un-level ground, your DJ/friend/sister’s boyfriend is now a no-show and you need to find a new one ASAP. Consider it your emergency savings for your wedding. We recommend budgeting 8-10% of your budget for overages.
3. Not budgeting for a rain plan. One of the biggest mistakes I see when coming late to the game with brides. A bride planning an outdoor wedding who convinces herself it won’t rain on her day usually gets the worst surprise of her life when a week out she’s faced with a 90% rain chance and no budget for tenting. Rain plans are unfortunately an expensive and necessary evil, so put the money aside and consider it spent until you get the 48 hour forecast. Most basic tents start at around $600.
4. Consistently going over budget in every category. A good budget is set up to be flexible, but, if you are consistently going over in every category (even $100 or so) you will find yourself quickly reaching into an empty pocket book. The best way to approach this is to talk to your fiancé and decide what areas you’d be willing to splurge on, and how much you can afford to splurge. After you’ve talked about potential overages, stay in budget in the other categories, no matter what. Chances are you will come under in other areas and come out on top.
5. Details, details, details. Not factoring in the small items can be a budget breaker. For example, you may have booked rentals, but did you factor in delivery and set up? ($300-$500)What about your guest book? ($20-$50) Those champagne flutes for toasting? ($20-$200) All of these items need to be accounted for. The best way is to start with an overly intensive budget and work your way through it, deleting anything you don’t need. Being too general with your categories can make it very difficult to get accurate estimates.