Consider how fancy or casual you want to go with your wedding day, as that decision will affect the number of guests, the food, the decoration, the entertainment, and the debits to your wedding funds, as well as your wedding style.
Personal preference is a key element in determining which degree of formality best suits your wedding. But the formality of your wedding will be reflected first and foremost in the location, as well as the time of the day and season. Consider the dress code here, too: for instance, if you have decided on a beach wedding, probably makes more sense to go informal or semi-formal than asking your guests to wear a tuxedo or or a long gown, in the heat and sand.
Whatever you decide, you'll want to carry your chosen formality through every part of your wedding. Relax, there are only four degrees of formality when it comes to getting married, and in choosing one of the following, think which one best suits your personalities and vision.
Ultra-formal. A ballroom or grand hall type of venue, complete with a twenty-four-piece band and over the top centerpieces. This kind of fancy style, only works in the evening and requires the most formal of all dress codes, with white or black tie for guys and full-length gowns for the ladies.
Formal. A late afternoon or evening affair that's slightly less formal than a black tie event and might be at a museum, historic building, or picturesque estate. A tuxedo isn't required, but the event is still formal enough for one to be appropriate; it's casual enough for a formal dark suit and tie to be suitable, as well. Women can choose a fancy cocktail dress or a floor length gown. Black-tie-optional and cocktail attire dress-code instructions both fall under this category.
Semi-formal. A late afternoon or evening affair that could take place anywhere from a country club or loft to a winery or restaurant. Cocktail attire is a must, with a suit and tie for the gents and a cocktail dress for the ladies.
Informal. Anytime and almost anywhere affairs (backyard ceremony, rustic barn, lodge or beach), with ties optional for the men and sundresses or skirts for the women.
Now that we have taken a look into the four main categories of formality for a wedding, let's clarify the difference between the expression: black tie event and black tie optional.
A black-tie-optional leaves a bit more room for interpretation. A tuxedo isn't required, but the wedding is formal enough that one would be appropriate. Otherwise men should go with a dark suit and tie. Women also get a little more leeway. For a black-tie-event instead refer to the Ultra-formal definition.