A 40th has a guest list that mostly cannot simply turn up. Friends have young children, partners are invited, and the answer to your invitation depends on whether someone can arrange childcare on that specific night. Everything that makes that arrangement easier converts directly into people in the room.
The single biggest lever on attendance at a 40th is the start time. An 8pm start means a babysitter until well past midnight and a guest doing the arithmetic on whether it is worth it. A 6:30pm start gets the same people there for the same length of evening.
If the party runs late anyway, say so — "from 6:30, and it will run late" lets people come early and leave when they need to without feeling they have failed to stay.
Every parent on your guest list is deciding whether this is an event they bring children to, hire a sitter for, or split so one of them stays home. If the invitation does not say, they will guess, and a guess usually resolves into a decline.
Say it outright. "Grown-ups only, sorry" is a perfectly good line and lets people book a sitter early. "Kids welcome, there is a garden and a film on" is a different party, and it will change who comes.
Six to eight weeks is right for a 40th, longer than you would give a casual birthday. Childcare, weekends away and other people's milestone parties all get booked further ahead at this age.
A save-the-date message even earlier is worth it if the date is a Saturday in a busy season. It costs you one text and protects the date against everything else being planned.
A 40th that starts at 7pm with "nibbles" and a 40th that starts at 7pm with dinner are different evenings, and guests need to know which so they can feed themselves and their children beforehand.
If you are catering per head, ask guests to confirm numbers rather than replying yes — partners are frequently assumed rather than counted, and at this size the gap is expensive.
Dan is turning 40 and would rather see you than not. Saturday, September 19, from 6:30pm 61 Hallam Street, Brooklyn, NY 11215 Proper food, not just snacks. It will run late. Grown-ups only, sorry — we thought you might appreciate the excuse. Please reply by September 5 and tell us about any dietary needs.
Forty years of Sarah Friday, May 8, 7pm The Cedar Room, Ashcombe Hotel Three courses and a toast. Partners very welcome. Please confirm how many of you are coming by April 24, along with anything you don’t eat.
Come and mark Ben’s 40th with us Sunday, July 12, 3pm until late 4 Warwick Gardens Kids very welcome — there’s a garden, and a film on later for anyone who has had enough of the adults. Barbecue from 4. Let us know numbers by July 1.
Earlier than you think — 6:30 or 7pm. Most of your guest list is arranging childcare, and an earlier start gets the same people there for the same length of evening at half the babysitting cost.
Either answer works, but the invitation has to say which. Parents who are left guessing tend to decline, and those who know it is adults-only can book a sitter while there is still one available.
Six to eight weeks, which is longer than a casual birthday. Childcare and other people's plans are both booked further ahead at this stage.
Ask each guest to confirm how many people are coming rather than replying yes. Partners are the most commonly assumed guests at a 40th, and if you are catering per head the difference is expensive.
The first milestone people actually throw a party for — and the one where a bar tab depends on the number.
Three generations in one room — an invitation that works for a college friend and an aunt alike.