How many guests for a birthday party? The maths

It's the Sunday before the party. You have a notepad, a pen and a column of first names that keeps getting longer: nursery friends, two cousins, the neighbour's twins, the parents you actually talk to. Then someone asks the question you've been avoiding all week — how many people are you feeding? The cake has to be ordered by Tuesday.

So: how many guests for a birthday? It isn't a feeling you wait for. You can work out the number in ten minutes with three things you already know — the age of the birthday person, the space you're using and what you can spend. Everything after that is arithmetic.

How many guests for a birthday? The age sets the style

A party for a five-year-old doesn't run like a fortieth. Small children need one simple rule, teenagers need a crowd, and adults need a table where everyone can hear each other. Pick the bracket first and the rest of the list fits around it.

• Small children: one friend per year of age, plus siblings. Five years, five friends.
• By ten: that rule runs short. Ten to twelve guests is the usual landing spot.
• Teenagers: the group decides, not the seating plan. Past 25 guests you need floor space and music, not a long table.
• Adults: a round table seats eight to ten comfortably. Thirty people means a standing party, not a dinner.

Your room sets the ceiling before the list does

At home, count 1 m² per seated guest and roughly 0.5 m² per person if they'll be moving around. A 20 m² living room takes a dinner for 12 to 15, not 30. Restaurants and hired rooms usually have two capacities — seated and standing — and prices that move in bands, often in tens. Ask both before you confirm anything. If the plan is a park or a terrace, keep a smaller Plan B for rain and say so in the invitation, so nobody turns up to the wrong version.

Then do the division. Take the money you can spend and divide it by the cost per person — menu, cake, drinks, the small thank-you gift. That's your maximum: €600 at €30 a head is 20 guests. Hold two or three places free for the replies that always arrive last, because the guest list almost never closes exactly where you planned. And each extra name isn't just a plate: it's a chair, a slice of cake and another glass.

How many guests for a birthday isn't a matter of taste. It's age, space and budget — then a link that counts the replies for you.

The replies are the part nobody plans for

The birthday group chat fills up with "yes" and "probably", and none of it tells you how many chairs to rent. A digital invitation from Send The Joy is a web page for your party, shared with a link, a QR code or a message. Guests don't install anything: they open it in their phone's browser and answer there, so the confirmations arrive in one ordered list inside the invitation, and you can set the questions yourself. It costs €29.99, one payment, no subscription, and you can try it free in test mode before you decide. Edit it after sending and the link stays the same — change the time, the address, the map or the dress code, and everyone sees the updated version without a single forwarded message. Sort out your number, then publish.