Formal invitations to events, weddings and parties dictate a formal reply in return, whether you are accepting or declining the invitation. It makes the event planning significantly easier for the host to receive a response from everyone; sending a note to decline helps clarify headcounts.
Check the box next to the "decline" option on the response card if provided.
Write a short note if no response card is provided. This can also be included even if a response card is provided on an additional piece of stationery..
Begin the note formally and in the third person, echoing the way the host addressed the invitation to you. For example, write; "Ms. Jessica Smith regrets that she must decline your kind invitation."
Include the reason why you cannot attend. For example, "Ms. Jessica Smith regrets that she has a prior commitment on that date and must decline your kind invitation."
Close with good wishes for the event. For example, write; "Wishing you the best of luck on your special day."
If there is no time frame included on the invitation to R.S.V.P., it is in good etiquette to decline a formal invitation as soon as you know you will not be attending or at least four weeks prior, so that the hostess has time to get the venue an accurate headcount. If there is no response card included in the invitation and you wish to mail a response anyway, try matching the quality of the stationary you use to the quality that the hostess used in the invitation. Elements in the invitation to make note of are the colour of the paper, the weight and stock of the paper as well as whether the invitation was handwritten and printed.