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AIBU?

Share your dilemmas and get honest opinions from other Mumsnetters.

Birthday bill split

1000 replies

KnickerlessFatWoman · 18/07/2026 12:55

Last weekend was my mother’s birthday, so we - that’s me, my parents, sister and BIL and their 12 year-old son - went for Sunday lunch. Unfortunately the food wasn’t great, and they ended up taking my main off the bill.

My dad is someone who always wants to treat everyone, so my sister and I decided this time it was our turn and we were going to treat him and our mum instead. When the bill came, BIL asked if we could split it over two cards, but they said they could only take one payment. He paid and I said I’d transfer my share. For the sake of keeping the maths simple on this thread, let’s say the bill was £210, or £35 per head.

Both BIL and sister are crap at responding to messages, so it took me until midweek to get the bank details. I sent over £70 to cover me and one of my parents.

I heard nothing in response, but I was chatting to my mum earlier and she said “Oh, by the way, Katie said you got the money wrong - it was £210 and you only sent £70”. I said no, that was right - my meal and one other. She said, “Ohhh… I think she thought you were splitting it”. I laughed and said, “No, we said we’d treat you and Dad. I didn’t say I’d pay for three meals!”

I don’t really know why my sister couldn’t just have messaged me instead of talking to our mother about it, but that’s not really the issue. Surely she and BIL don’t expect me to pay half the bill? By treating our parents, I meant exactly that - not that I’d pay for them both while my sister just paid for her own family (which is what this amounts to). There are three of them and one of me. If I pay half the bill, sister and BIL have only covered themselves and their child - there’s no “treating” anyone at all.

AIBU for thinking £70 was my share and paying just that?

OP posts:
KnickerlessFatWoman · 18/07/2026 13:12

Recklessismymiddlename · 18/07/2026 13:07

I’d have thought split the bill £105. I wouldn’t be quibbling for a sister and nephew tbh. But I also wouldn’t have involved my mum if I was your dais.

Can I ask why you think that would be “quibbling”? I’m not having a go - I’m genuinely interested. To me, it’s just common sense that an adult wouldn’t expect their SIL to partly absorb part of his and his child’s costs.

OP posts:
arethereanyleftatall · 18/07/2026 13:13

You are right op. Some people just don’t understand very basic stuff.

backformoreofthesame · 18/07/2026 13:14

Op agreed to pay towards the parents meals not a load of additional people - how greedy to expect to benefit from someone else’s birthday !

cakeisallyouneed · 18/07/2026 13:14

Call your dsis OP. Nip this in the bud. Tell her your mum has passed on the message. It’s a miscommunication, explain your side. You’re splitting mum and dads bill not the whole bill, as the latter would mean you were paying for both parents and dsis only pays for her own family and you wouldn’t have agreed to that. Tell her to reach out to you next time rather than going through your mum. Agree to both be clearer next time.

SunnyRedSnail · 18/07/2026 13:15

lifeturnsonadime · 18/07/2026 12:58

I think DSis is right, if the intention was to split the bill in half then it would be £105 each.

Did you think your parents were paying for themselves?

The intention was to treat the parents.

E.g. pay for THEIR meals. So OP pays her meal, DSis pays for her family then they go halves on the parents share.

If they paid 50% each of the entire bills then that's just the OP taking her parents out. The sister wouldn't be treating anyone.

@KnickerlessFatWoman just message your sister and say there seems to have been some confusion and you were under the impression that they wanted to treat the parents, hence paying half the cost of their meals each.

Moonnstarz · 18/07/2026 13:15

I have had to read this several times and to me you said you were splitting the bill so I would also assume that meant half. Obviously this is a disadvantage to you as you would be paying more, but that is where I think the confusion lies.
I think you needed to say I will be paying for myself (even though yours ended up being free) and mum.

KnickerlessFatWoman · 18/07/2026 13:15

SpottyPyjama · 18/07/2026 13:12

I’m with your sister. The treat was a meal out with the whole family, so if you agreed to split the treat 50/50 you pay half of what a meal for the whole family costs.

It seems like there was a misunderstanding, but you don’t have some moral high ground here or the automatic right to claim your sister was wrong.

But all they’re split does is cover their own meals! They wouldn’t have paid anything towards my parents’ meals!

OP posts:
MeanwhileinGilead · 18/07/2026 13:15

Based on this: my sister and I decided this time it was our turn and we were going to treat him and our mum instead it seems pretty clear that you and your sister would each pay half of the costs incurred by your parents. Unless there was more discussion, there's no indication of a further split, and no need for one. Some people do split the whole bill equally by default because they think it's easier or requires less discussion and potential disagreement, but that rests on at least the premise that the portions will be roughly equal. This isn't a situation where you and your sister each brought a partner and child and you're quibbling over who had an extra glass of wine or steak instead of chicken. It's really unlikely that your bill for one person would ever have equalled or exceed your sister's, BIL's, and nephew's bill for 3, so your sister is expecting you to partially treat her and her partner and son for your mother's birthday when you never offered to do so. She's taking advantage whether she consciously realises it or not.

As an aside, I'd be really annoyed to hear from my mother about this - surely the main point of you and your sister treating is so your mum and dad don't even have to think about the costs and can just enjoy the birthday mean?

Coconutter24 · 18/07/2026 13:15

KnickerlessFatWoman · 18/07/2026 13:11

As I say, I’ve only just found out that she’d understood the plan differently to me.

Then I would call her now and talk with her about it. If someone says split the bill it does usually mean 50/50 of the total not 50/50 of just part of it. I do agree you’ve paid your fair share otherwise like you say if you paid more you’d be paying towards your sisters share

EvangelicalAboutButteredToast · 18/07/2026 13:17

KnickerlessFatWoman · 18/07/2026 13:08

But if you do that, where is the “treat” from the other side? My sister agreed we’d treat our parents - if we split the bill 50/50, she isn’t contributing anything.

I can see why there was a misunderstanding.

i tnink you are saying that your father usually pays for everyone, so your sisters family usually pay zero. You agreed to ‘split the bill’ and from your sisters point of view that meant half each, I think. I would have thought the same. If what you meant was that you and your sister would cover your parents’ meals then that’s a whole different sentence.

mindutopia · 18/07/2026 13:17

Your sister obviously was hoping you meant literally splitting the bill.

But you’ve done the right thing. You’ve paid for yourself and split your parents’ portion. I guess it would only be unfair if your parents collectively ate more than £70 worth of food. A 12 year old for example probably wouldn’t eat a £35 meal unless he also had 2 ciders.

So it’s really more of a question if £70 covers your portion (did you have 3 wines?) and is actually half of your parents’?

backformoreofthesame · 18/07/2026 13:18

SIL wouldn’t have paid anything and yet expected to get credit for the treat if she had her way on the bill !

OP tell your mother you though the treat was from both of you, not just you

SpottyPyjama · 18/07/2026 13:18

KnickerlessFatWoman · 18/07/2026 13:15

But all they’re split does is cover their own meals! They wouldn’t have paid anything towards my parents’ meals!

No, but they would have paid half towards the special occasion. Presumably it wouldn’t have been as nice a treat for your parents if their grandchild hadn’t been present, so the treat was a meal out with the whole family.

If all you wanted to do was pay for the parents to have a meal then you could have given them a voucher so they could go out by themselves.

HateThese4Leggedbeasts · 18/07/2026 13:20

I think what you did is fine. Maybe your dsis agrees which is why she hasn't said anything to you directly.

My DM does tend to accidentally get in the middle of me and my siblings sometimes by misunderstanding passing comments as "problems" and telling the others. Could that have happened here?

MyDeftDuck · 18/07/2026 13:20

Based on the fact that your main was crap, and deducted from the bill I think you’ve been more than generous in paying £70!

arethereanyleftatall · 18/07/2026 13:20

My jaw is on the floor with the amount of people that don’t understand that your sister has 3 people in her family, you have 1, your parents are 2; so if you each pay for 3 they aren’t treating their parents at all, you are entirely. This really isn’t rocket science. Op, you are not wrong but if your sister has the grasp of maths same as sone people ok this thread, then good luck explaining it.

OhLaDiDaDiDa · 18/07/2026 13:22

Yanbu. Your dsis is wrong.

MsAmanda · 18/07/2026 13:23

You are both right as you both believed you understood what each other meant. If it was my sister and her family, I’d have split the bill down the middle. You don’t have to. Just explain your understanding was different and leave it at that.

lifeturnsonadime · 18/07/2026 13:23

arethereanyleftatall · 18/07/2026 13:20

My jaw is on the floor with the amount of people that don’t understand that your sister has 3 people in her family, you have 1, your parents are 2; so if you each pay for 3 they aren’t treating their parents at all, you are entirely. This really isn’t rocket science. Op, you are not wrong but if your sister has the grasp of maths same as sone people ok this thread, then good luck explaining it.

It's nothing to do with not understanding maths.

The arrangement OP wants is not the 'splitting the bill' arrangement that was made in advance. If 2 people agree to split the bill they pay 50% each.

If OP didn't think that was a fair arrangement she should just have said she'd pay for her and one parent rather than saying she would split the bill .

BangBangBangBangBang · 18/07/2026 13:23

Your way of doing it makes much more sense. Sounds like there was a miscommunication but if she thinks about it for 5 seconds she will surely see that a 50-50 split just means that she's paying for her family and you're paying for both parents.

Loulou4022 · 18/07/2026 13:23

I think it needs a conversation in future to agree details as looking at this thread everyone obviously has different expectations of what is fair. There is no right or wrong so needs agreeing beforehand. In this case my opinion is they are being cheeky fuckers! I assume there’s 2 of them working and they’re expecting you as a single person to cough for half of the bill!

FateAmenableToChange · 18/07/2026 13:24

Id text her and clear it up, she's going around telling lies about you. Ask her if she intended that you pay for them and your parents?

musicandmen · 18/07/2026 13:24

I would expect 50% if we were splitting the bill. That was the deal

PrincessScarlett · 18/07/2026 13:27

Trouble is that you agreed to split the bill which in most scenarios implies 50/50. What you should have said is that you will pay for one parent and sister pays for the other. I don't at all think you should have paid anymore than you did but your sister isn't unreasonable to be pissed off when she thought you'd agreed to split the bill.

Better communication is needed. Although your sister is out of order to be moaning to your parents about it.

As an aside, you said BIL wasn't drinking (and neither would their 12 year old). Was a lot of alcohol consumed by the drinkers? As that would also be a bone if contention to those not drinking.

canklesmctacotits · 18/07/2026 13:28

You said your dad always treats people - ie pays 100% - but that your sister and you agreed that this time you would split the bill between you - ie you both pay 100% of the bill.

You didn’t say that you would pay for one parent each in addition to your own meals. That’s a huge gap in misunderstanding and miscommunication.

“Split the bill” means divide the whole thing by the number of people paying. “Treat our parents between us” means each paying for one parent.

And no, you won’t have paid for both parents and she none. You would have paid for yourself, one parent and someone else.

That’s what “splitting the bill” means. If you don’t want to do that, use different (correct!) words.

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