Wedding Etiquette 101: Everything You Need to Know

Keep in mind that timing is of the essence when altering an R.S.V.P. “Most catering companies want a final guest count somewhere in the 10 days to two weeks range, and if you’re able to change your R.S.V.P. before that time,” Ms. Savage said, the couple won’t have to pay for your food. Revoking your attendance at the eleventh hour? According to Ms. Randall, the only suitable reasons to do so include a death or serious hospitalization, a sudden lack of child care or a flight cancellation.

On the other hand, perhaps you’re overjoyed about the prospect of watching a loved one tie the knot — so much so, that you’re inclined to ask whether your new beau can join the festivities. Is it suitable to do so? “That’s an easy no for me,” Ms. Savage said. “I wish I could say otherwise, but making the guest list is probably the most fraught decision that couples have to make.” And, she said, “If you’re close enough to the couple that they would know you now have a significant other, then they will extend an invitation if one is available.”

Other experts express differing sentiments. “Surely, the people who are inviting you also want you to have a great time,” Ms. Lee said. “If you are really involved with somebody else, you have to just tell them.”

However, you’ll first want to do a bit of research — such as consulting your save-the-date card. “If there’s not ‘and guest,’ I would make sure that they are allowing other plus ones,” Ms. Palladino said.

Consider bringing your request to someone closely involved in the wedding planning process, Ms. Hirst said. “Put a feeler out first, because the last thing you want to do is add more stress to any couple who’s getting married.”

The maxim that wearing white to a wedding is discourteous holds true today. “It doesn’t matter how old you are, if you’re in a cream dress or a cream suit, you’re going to stand out,” said Alison Bruhn, a founder of the Style That Binds Us. Ms. Bruhn, a personal, wedding and executive wardrobe stylist based in New York, also advises steering clear of outfits that are “super sexy or revealing” and suggests keeping a wrap handy to cover exposed shoulders in houses of worship. With contemporary dress codes ranging from black tie to festive, deciphering the intricacies of invitations can often be challenging.

“Instead of asking everybody else … go to the source,” said Ms. Bruhn, who encourages guests to contact the couple or their event coordinator. Ms. Savage, who agrees that wearing white is generally a faux pas, offered additional guidance. “Please don’t show up in jeans and a T-shirt. Life isn’t that casual on a wedding day.”