Person whose birthday it is should not pay for meal

I think it depends on the groups you mix with.

Us, middle aged, financially comfortable, general rule is if you invite, you pay (for a birthday/anniversary/celebratory meal), but if it's just a Saturday night meal out then the bill is generally split. For student DCs, they'd each pay for themselves regardless of the occasion as neither they nor their friends would be in a financial position to pay for everyone.

It's the norm for everyone to assume they're paying their own, or splitting the bill in my family.
To offer to treat everyone on your birthday is very generous. But it could be that there's a few guests who might struggle to easily afford it, and she wants to guarantee they'll come along.
Tell her you don't think it's necessary but if she insists then just make a fuss over her and maybe order and pay for some champagne/ nice wine for the table? Or offer to cover the tip, or both.
I'm sure it will be lovely. If she can afford it then I'd just enjoy it.

Traditionally, the person who invites pays. It's up to your mum and your family whether they want to be traditional or not.

Gosh I don't think your Mum should pay for herself never mind anyone else on her birthday .

I don't understand why this is an issue, op, unless your mum is being pressured or can't afford it. People celebrate birthdays and pay for things in very different ways, there's no 'standard' or 'usual' in this scenario. In my family, we pay for our own. In dh's family, his dad normally pays for everyone.

It's about what the person whose birthday it is wants not other people who insist it is their way

You clearly don't know my lovely mum.

family birthdays are difficult to navigate, perhaps mum wants to pay because she knows some attending don't have as much as others and wants to treat people and make it fair?

I had 2 60th birthday parties, 1 family one abroad, which I paid for catering, my brother, and sis in law paid for booze and cake ( 18 in all).
My second party was with close friends and neighbours, at the pub, I offered and did pay for their food, up to £25 (in 2022), cake was a gift and drinks they paid for, 16 in all.

i didn’t want to make my friends think about if they could afford to come, my house is too small to invite them here.
Everyone said how they enjoyed themselves tho

I pay if I invite or organise a meal out.

I'd also be fine with paying for my own meal and for the birthday boy or girl also.

Leave your mum to do as she wishes, she's all grown up and you should respect her choice.

Why don't you organise a really lovely cake to bring which can be a surprise so she doesn't end up covering dessert for everyone?

As others have said, everyone has a different view on this.

When younger and out with friends (school/uni days), we used to split the bill and share the cost of the person who's birthday it was irrespective of who organised the meal.

My parents generation would be absolutely horrified at allowing anyone else to pay if they have invited others out to celebrate. They strongly believe they should foot the bill. Over time, I agree with this more and more and want to pay if I were inviting anyone to celebrate my birthday/anniversary/occasion

In some cultures it’s normal for the birthday person to pay for everyone’s meal - like when you invite children to a birthday party, you don’t expect the parents to chip in for the room hire.

If your mum genuinely wants to treat everyone, let her.

If I invite people out I like to pay. Perhaps your mum wants to do the same?

Yes this. Totally normal for the birthday person to pay for everyone for a formal meal. Please don’t try and pay for yourself, that would be very rude and gauche.

If my lovely mum was kind enough to bring our family together and pay for us to eat together, I'm sure we'd all be very grateful

I think it highly likely that there will be someone at that table who is there under sufference: least favoured sibling, in-law, adolescent grandchild etc.

My mum would definitely pay for everyone.

That's very generous of her
I mean I guess if she can afford it and wants to 🤷‍♀️

Unless you (or anyone else) has put pressure on her to pay for the whole lot, or you think she really can't afford it, then why not just let her pay?

It's normal in my family for my parents to pay for family meals. My father would be mortally offended if we tried to do anything else.

What a mean-spirited response.

If my lovely mum was kind enough to bring our family together and pay for us to eat together, I'm sure we'd all be very grateful.

It’s really up to her, why are you trying to overide her?

The only thing that really matters, is that everyone who is invited is clear on whether they are expected to pay for themselves, chip in to pay for the birthday person, or whether the bill is being covered by whoever is doing the inviting.

I am so thankful that I've never had to suffer the dreaded "family meal". But if an adult summons an entire clan to celebrate their birthday then, yes, they can darn well pay for it!

There's no right or wrong, it's a choice but best to make sure everyone knows what's happening.

And just to add, I think it is incredibly important and much better manners to be able to graciously accept other people's generosity. If your mum wants to treat her family, then for god sake let her do it. She is literally telling you what she wants, it's very infantalising to insist you know better.

I don't think there are fixed rules, it depends on context.

A casual get together with friends to celebrate a non-milestone birthday - would be normal for guests to pay for themselves, and also quite normal for the guests to cover the birthday person's meal as well.

A more 'formal' event (not necessarily a formal venue, but where people are formally invited by the host) - perhaps a private dining room etc - it would be perfectly normal for the birthday person to act as 'host' and pay for everyone. And it would be quite rude/odd to suggest paying (like trying to pay for your meal at a wedding).