“My two cents’ worth” is an opinion. The idiom comes from 15th-century British use of twopence or tuppence to mean “of little or no value.” The American “two bits,” meaning 25 cents, is used in a similar way.
In the past, many goods or services have borne a low price, such as twopenny ale, twopenny post, even twopenny rope (an archaic idiom for a flop house). In the bible, (Mark 12: 41-44) the “widow’s mite” was a donation of two mites (the smallest coin) to the temple.
The use of “two cent” and “twopenny” as dismissive descriptions of items of very small value dates to 1560. For example, “Even in a two-peny matter” (1643), and “He cares not two-pence for the land-tax bill” (1744).
But, “Here’s my two cents” in the sense of airing an unsolicited opinion dates only to the mid-1920s.
No one knows how the idiom first arose. Perhaps because, at one time, it cost two cents to mail a letter which no doubt contained one or more opinions. Some people have suggested that the ante in a poker game was two cents, therefore one would “ante in” (enter a conversation) by throwing in one’s metaphorical two cents. While the gambling explanation sounds attractive, nothing supports it.
But why do we say, “Here’s my two cents” instead of “Here’s what I think”?
We do so to lessen the effect of a possible social trespass. By identifying one’s take on a matter as being worth no more than two cents, some of the social crime of butting in unasked is undone — the advice is offered in a self-deprecatory, “Well, this likely isn’t worth all that much, but here it is anyway” fashion. The one who inserted himself presumptuously into something that wasn’t his business, is at least being humble about it.
A similar idiom is “for what it’s worth” and is often used to offer opinions or information, suggesting that these may not be important or valuable or that the person being addressed may not care, but you’re going to say it anyway.
The US Treasury Department issued a two-cent coin in 1864. Was the Treasury offering an opinion? No, but the two-cent coin was probably discarded as being useless long before Canada’s copper penny bit the dust.
I miss the copper penny, even if it wasn’t worth two cents.