I learned that this greeting, although primariy used on birthdays, can also be used at Christmas and New Years. The terms, it seems, refers to time...of the passing year.
Since the 1700's, this saying has been used to express the sentiment that a celebratory day would "return" or recur many more times. Prior to the mid-19th century, it was used on all festivals and celebrations. Lately, it's become a more formal way of wishing someone a happy birthday.
The earliest attributable reference goes back to 1789 and was used by Lady Newdigate, on her wedding day, to wish her new husband a long and happy marriage. But there is, still, a much earlier reference to this phrase. It dates back to Roman times and was used to wish a man "many happy Returns of it." Why "returns" is capitalized, is anybody's guess. We do know that the phrase is more common in British and Indian English than it is in Canadian or American English.
An alternative explanation says that "returns" can also mean yield or profit. Using this theory, our phrase, 'Many happy returns of the day' comes to mean wishing the person a rewarding day; one filled with much happiness. Joseph Addison, in 1716, is first credited with using the phrase in this way.
And let's not forget our friend Winnie-the-Pooh...
His preferred method of wishing his friends a happy birthday was to wish them "Many happy returns of the day." And what better expert can you get than a cute, little bear?
If today is your birthday, let me be the first to wish you, "Many happy returns of the day."