Black Tie Optional
What it actually means
The host is signalling a formal evening but giving you room. You can wear black tie, or a formal dark suit and a dressy floor-length or elegant midi dress. The safest read is to lean formal.
The safe choice
A floor-length or elegant midi gown in an evening fabric. You will always be right if you dress as though it were black tie.
Too formal
White tie or a tailcoat is beyond what is being asked.
Too casual
A casual day dress, a lounge suit, or separates that would suit brunch. 'Optional' does not mean casual.
Common mistakes
- Reading 'optional' as 'casual' and underdressing
- A business suit instead of a formal dark suit or tux
- Daytime fabrics like linen or cotton poplin for an evening event
- Assuming the crowd will dress down - it is safer to dress up
By country & season
In the US this leans quite formal. In Europe there is more latitude toward a smart dark suit. Warm-weather events allow lighter colour and fabric while staying formal.