Joint kids’ birthday party: how to split the costs

Three kids in the same class have birthdays in March, and their parents decide to throw one party. It saves time and money, but the guest lists are not the same size, a little brother joins in, and one family paid for the venue while another ordered the cake. So that no one leaves feeling they paid for someone else, split each expense by whatever makes it go up.

Two kinds of expenses

Some expenses grow with each child invited: admission to the play center or workshop when the venue charges per child, party bags, sometimes snacks. Split those by how many children each family invites, their own child included.

Others stay the same however many guests come: the cake, the decorations, a flat-rate room rental. Those benefit all three birthday kids equally, so split them evenly between the families.

A brother or sister who takes part in the activity counts as one of their family’s guests. If they only drop by for cake, they change nothing. Decide this before booking, when you set the lists.

A worked example with three families

This example is fictional. Leo, Ines and Sam celebrate together at a trampoline park that charges $15 per child. Leo’s family brings 9 children (Leo and 8 friends), Ines’s family 7 (Ines and 6 friends), Sam’s family 6 (Sam, 4 friends and his little brother). That makes 22 children.

• Leo’s parents pay the park: 22 × $15 = $330.
• Ines’s parents pay for the cake, $72, and the decorations, $33, so $105.
• Sam’s parents pay for 22 party bags at $4, so $88.

The party costs $330 + $105 + $88 = $523. Here is each family’s share:

• Leo’s family: 9 × $15 = $135 for the park, $105 ÷ 3 = $35 for cake and decor, 9 × $4 = $36 for party bags, so $206.
• Ines’s family: 7 × $15 = $105 for the park, $35 for cake and decor, 7 × $4 = $28 for party bags, so $168.
• Sam’s family: 6 × $15 = $90 for the park, $35 for cake and decor, 6 × $4 = $24 for party bags, so $149.

Check the total: $206 + $168 + $149 = $523. Three equal shares would have been about $174 each: Sam’s family, which invites the fewest children, would have paid about $25 too much.

Who pays back whom

Compare what each family paid up front with its share. Leo’s parents paid $330 for a $206 share: they are owed $124. Ines’s parents paid $105 for $168: they owe $63. Sam’s parents paid $88 for $149: they owe $61.

• Ines’s family sends $63 to Leo’s parents.
• Sam’s family sends $61 to Leo’s parents.

Leo’s parents get back $63 + $61 = $124, and the three families are even after two payments.

Gifts and last-minute changes

Guests do not pay for the party, but they often wonder whether to bring three gifts. Say it in the invitation: one gift for the child who invited them, or an optional contribution to one gift per birthday kid. That money stays separate from the party costs.

If a guest does not show up and the venue still charges for the spot, that cost stays with the family who invited them. If the venue does not charge for it, just remove one child from that family’s list before you do the math.

For a vacation shared by families with kids of different ages, see sharing a vacation rental with several families. For a party where the hosts share the costs and guests share a gift, see splitting baby shower costs among the hosts.

Keeping track between families

In Spliz, the three families can add each expense, split it evenly or with different shares based on the number of children, and check each family’s balance. The other parents join the group by installing the app, without creating an account. The app does not move money: repayments happen by bank transfer, in cash or with another app, then get recorded so everyone knows they are done.

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