How would you split the cost of this trip?

This.

@GetBendyWithWendywhat has your sibling proposed in terms of cost split?

I’ve a dh and one dc and a single sibling. If it were me and my family needed 2 of the 4 bedrooms (which increases the cost) then I’d pay half and let my sibling and parents pay 25%. If I felt my parents couldn’t afford it then I’d just pay for them. If sibling and I arranged it fully then we’d both pay for our parents.

Whose idea was the trip? If parent 1 was involved in the plan they should pay something and the 25:25:50 split seems fair, but if the idea came from the children then I think split it 33:67.
With the qualifier that if the idea was only one child's and they imposed it on others, then they maybe ought to pay more especially if they are in a better financial position than others.

Your family sounds so nice, reasonable and normal.

I know you’ve said it was mutual but if the other parent was the one to say “ shall we all go away together for x birthday “ then I’d expect them to pay for the parents. Then the two adult children to pay for themselves and their families ( appreciating one is single so would only pay for themselves ) . If it was either of the adult children who made the initial suggestion I’d do single adult pays for themselves and one parent. Married adult pays for their family and other parent. Try not to get too hung up and think of the benefit of getting along and having family time together as something you’re also paying for and are lucky to have. If this all causes grievance sorting the shopping bill / who pays what for a take away etc will be miserable.

It all seems very dramatic. Here, either the parents would pay for everything, or the children would split it, probably 50/50 but with the married sibling offering something extra.

It wouldn't be done as a surprise though because IMO that's all about givers, rather than the receivers. Let the birthday girl/boy look forward to the trip and plan their own wardrobe.

In my family. We would just split this between siblings and absolutley wouldn't expect the other parent to pay.

This sounds like really hard work. Family going away together for a birthday celebration. It’s not really relevant that the birthday person doesn’t know.
You need 4 bedrooms so parent pays for one, family pay for two, single child pays for one.

Food costs split in same proportion or 2/5 parent 2/5 family 1/5 single child - regardless of what teen eats they have no income.

If there is an actual present to be given that should be split 3 ways between other parent and adult children. Spouse and teen do not have to pay a separate share.

We've long gone past that stage, and they're not a saint We just
all know that life shakes down in different ways. The sibling who has more DC does more caring duties. The sibling without DC accepts a lot of help for another, entirely unconnected thing.

Paying a 3-way split for a holiday home twice a year or so is one small part of the fabric of ours lives and the give and take we're all part of.

You're not wrong, DoubtfulCat, which is why these things work if everyone's prepared to be fair, but not so much if someone insists that so-and-so won't be using much such-and-such, and then others look at them through narrowed eyes when they do

I guess it's a case of knowing the people concerned, and the very fact that OP's already concerned about "what's fair" seems to me to indicate a risk of this going south

And I wouldn’t consider the impact of a second earner in one of the adult children’s households.

Are you in a household with two incomes? It sounds like it ...

I'd split it four ways between the adults. It's not fair to split it between families. I would assume the adult child with a spouse and child would take two rooms at the accommodation anyway? And therefore it's justified to pay more.

I think paying by room is fair. So if the family with the teen requires an additional room, they pay more for accommodation. If they will share, then each family pays a third. Food should be split per person.

Is the other parent in on the suprise? If so, I'd say by bedroom.

For example:

Bedroom 1: mum and dad. In this instance the non birthday person would normally kick in for their room if it were my family, or half of it if others want to cover the birthday person.

Bedroom 2: married couple

Bedroom 3: kids

Bedroom 4: single person.

So if split 4 ways, non birthday parent pays 1/4.

Family pays 2/4.

Single person pays 1/4.

If kicking in for half of bedroom 1:

Non birthday person: 1/8

Family: 2/4 + half of room 1

Singleton: 1/4 + half of room 1

How many bedrooms in the house?
Whose idea was the trip?
In my family non birthday parent would cover the costs for all.

You aren't paying for people, you're paying for rooms. They're paying for the rooms that they use. Frankly if I'm going to quibble down to the last dollar about fairness I'm not going to go. I can't be bothered with that.

So the couple pays for their bedroom and their kid's bedroom, $500. The single adult pays for their bedroom, $250.

So for 3 people, that sibling contributes the equivalent of $186 per person, while the single adult pays $250.

Way to go for fairness!

Anyone that has bought me a night or two away for a birthday or Christmas has bought it for my husband and I.

-My mum sends us to Wales for two nights
-My husband's mum sends us to Paris
-We send our friend and his wife to Brighton

On all of these counts it could be husband or wifes birthday gift.

Never have I ever shouldered part of the spend on time away when it's directed at my spouse. These kind of gifts are to both of them because that is likely what makes them happier.

Horses for courses though I suppose

That's really, really unfair on the sibling without extra guests. My kids eat more than I do!

I think, if you’re quibbling about how the cost is going to be split, just don’t do it.
You’ll be counting pennies and tallying up debts the whole time. Who bought the food, the drinks, how much they had of the food and drink.

If you want to do this kind of break with family, the only way to do it is if you won’t begrudge paying for this or that or having less of the other because the trip is about the whole family rather than the individual units within it.

Your sibling with no children is a saint. When the children get older and a family can't fit into one room, I hope you split it more fairly.

I would pay per bedroom. Assuming there are four bedrooms and the cost is $1,000, each bedroom is "worth" $250.

So the couple pays for their bedroom and their kid's bedroom, $500. The single adult pays for their bedroom, $250.

Personally I wouldn't expect the parents to pay for their room at all but if you expect one parent to pay then they pay $125 and everybody splits the remaining $125.