I'm having drinks for about 40 people at home for my 30th birthday. Most people will drink wine and I am planning to buy it. How many bottles for that many guests?
Would you like your party to be a ''last days of Rome'' affair with orgies, backstabbings and an impromptu vomitorium off the balcony? Or do you have something less lavish and more refined in mind - perhaps an engraved card inviting guests from six until eight, some witty canapes, and an abrupt end to the drinks service at 8.30pm?
If the first is what you're planning, I recommend a minimum two bottles a person, a troupe of half-dressed slaves and a substantial investment in public liability insurance.
If it's the second, you can probably get by with a case of champagne and more gin than you'd think.
You may also need a spot of cream sherry for the great-aunties, and some cheap sauvignon blanc for your no-good girlfriends.
Assuming you're aiming for something between these two extremes, I'd suggest half a bottle a person. Not enough, you think? Your friends drink more than that? They probably do, given half the chance, but some will be driving and some will be pregnant.
Some will be taking part in one of those sponsored on-the-wagon months with cute names that help them feel better about binge-drinking the other 11 months of the year. For this mob, you will need a plentiful supply of mineral water, some orange juice, and maybe a not-too-naff mocktail.
A good host will make an effort on this front - providing an amusing non-alcoholic drink is an act of hospitality that makes parties more endurable for those who have to watch the rest of us getting socially overexcited.
On balance, if you're worried about running out, make it a whole bottle for each person. If you choose wine you'd drink yourself anyway, you'll probably buy it at a case discount and you won't mind having leftovers - what's not to love?
If you're not much of a wine drinker, store the extra bottles somewhere away from the light with a consistent lowish temperature and give them away next Christmas.
Are you struck with wine angst? Contact our Agony Aunt at firstname.lastname@example.org.