According to The Knot here are some helpful reminders when trying to decide on the perfect dress to wear to a wedding.
This is the most formal of all wedding dress codes and usually means the wedding is an evening affair.
Him: A tuxedo. If he doesn’t have one, he should rent one.
Her: A cocktail dress or long evening gown. Glamorous makeup and dramatic jewelry and hair are appropriate.
A semiformal wedding invitation can mean different things, depending on the time of the wedding. Lean toward a more formal look for an evening wedding, but slip into light colors and fabrics if it's a daytime wedding.
Him: A suit and tie, dark or light depending on the season and time of day.
Her: A cocktail dress, or skirt and top.
Generally, casual means anything goes. But for the purposes of wedding wear, assume business casual to be on the safe side. Also, assume that jeans, shorts, and tank tops are probably not appropriate unless they're specifically noted as acceptable.
Him: Dress pants with a button-down shirt or polo.
Her: Summer sundress, skirt, or pants with a nice blouse. Makeup and hair can be natural and everyday.
This suggests an elegant beach wedding -- so dress to impress, but also dress for the elements (sun, sand, and water). Anything you would wear to a nice restaurant on a summer day is appropriate.
Him: Summer suit and sandals.
Her: A more formal summer sundress with flat sandals.
With Love From the East Coast,