No one has to. That is the real answer, and it is not the one a gift shop will give you.
Debrett's is unambiguous: it is not customary to expect engagement presents, and no guest should feel obliged to give one. If you have been invited to an engagement party and are quietly panicking about arriving empty-handed, you can stop. Turning up is the gift.
So who does give something?
In practice, a small and predictable group.
Debrett's continues: "However, parents of the couple may choose to give a present, or perhaps a family heirloom. More practically, they may offer to make a financial contribution to the wedding, or the engagement party."
So the convention is parents, and only if they want to. Everyone else - friends, colleagues, wider family, the people most likely to be worrying about it - is under no obligation at all. If a close friend wants to mark the moment anyway, that is a personal choice, not an expectation being met, and it should be small.
Why so many people think they are supposed to give something
Two things create the pressure, and neither is a rule.
The party looks like a gift occasion. It has invitations, a venue, speeches and a toast, so it reads as a formal event of the kind that usually involves presents. It is not one. Its purpose, in Debrett's framing, is social: bringing two families and their friendship groups together so the wedding day is less socially burdensome, and so the wedding party know each other before the planning starts.
The retail calendar says otherwise. There is a whole category of goods marketed as engagement gifts, which exists because it can be sold, not because a convention demanded it. The same commercial logic filled in every year of the anniversary list.
If you want the shortest possible version to tell a worried friend: the wedding is the gift occasion. The engagement is the party.
What to do if you want to give something anyway
Reasonable, and common among close friends and siblings. Two principles keep it from landing awkwardly.
Keep it clearly smaller than the wedding present. If you are giving at both, the proportions should say which occasion is which. A large engagement gift creates an expectation you then have to exceed.
Make it about them, not about the wedding. Anything that contributes to wedding planning - a planner, a guide, a countdown - reads as an instruction, not a present, and it arrives before they have decided anything. Something that marks the engagement itself does not have that problem.
What is available at this stage is narrow, because the couple may not live together and there is no gift list to work from. The date they got engaged is one of very few fixed facts you have.
Acknowledge it by letter
There is one clear obligation in this whole area, and it falls on the couple, not the guest.
"Any presents or offers of money should be gratefully acknowledged, by letter, after the event." Not a text, not a group message on the way home. A letter. It is the one piece of engagement etiquette that is stated as a should, not a maybe.
That applies to offers of money as well as objects - if a parent has offered to pay for part of the wedding, that is acknowledged the same way.
Why the timing of the party matters to this question
The reason presents are not expected becomes clearer once you look at when an engagement party is supposed to sit.
Debrett's advises that a party is "generally held within a month or two of becoming engaged" so it still feels relevant to the announcement, and that it should not be too close to the wedding - because at that point "presents should not be expected". The engagement party is deliberately the cheap, early, sociable event. The gift-giving occasion is the wedding, months later.
Its actual purpose is social, not ceremonial: bringing the two families and their friendship groups together, so that the wedding day is less socially awkward and the wedding party know each other before the planning starts.
One trap worth knowing before you accept
This one catches hosts, not guests, but it shapes who ends up in the room.
People invited to the engagement party will assume they are also being invited to the wedding. Debrett's is explicit about it, and the simplest way to avoid the problem is to make sure every engagement-party guest can expect a wedding invitation too. Couples having a small wedding sometimes invite more people to the cheaper engagement party, which is fine - as long as it is said plainly, with the invitation, not left to be worked out later.
If you do want to give something anyway
Plenty of people will read all of the above and still want to mark the moment. That is fine; the point is that it is a choice, not a duty.
The two principles that keep it from being awkward: keep it small, and make it about them, not about the wedding. A present that is a contribution to wedding planning tends to feel like an instruction. Something that marks the fact of the engagement itself does not.
Worth reading next: what a personalised engagement present buys you, and what to write in the card, which for most guests is the whole gift.
The wider path: getting engaged covers who buys what, what it costs and what to write, before a date is even set.
