Is this dress too casual for a wedding

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I don't know the people getting married (it's my partners cousin, he's about 30). It's a registry office, then the rest of the day/night will be in an up market city centre bar/restaurant. I'm unfamiliar with the city, won't know anyone there except my partners 2 brothers who I don't know very well. None of them are any use whatsoever when asked anything about clothes/expectations or how posh the family /guests will be. I'm in my 40s but usually dress younger and very casual, and am a bit podgier round the middle than I'd like to be. I've tried a few things on in an attempt to be smarter and more age appropriate but I feel very middle aged in everything. I going to have to wear flat sandals and I feel like they'll work better with something longer. Apparently the bride is wearing trainers with her wedding dress and that is pretty much all I know.

I think it’s lovely and looks like it would be comfortable. I’m sure you will look gorgeous.🙂

I think perfect for that type of wedding

If there's no dress code on the wedding invitation then it's fine.

I would wear it.

Lovely and totally appropriate.

Love the dress! You could make it a little more formal if you like with shoes rather than sandals? Like plain low heeled pumps?

Based on the info you've given o think it's a great choice. Will you wear a jacket? What kind of shoes? Esska-type heeled sandals might work. I once went to the kind of grown-up wedding where you could wear a cool leather jacket over a gorgeous outfit and still look appropriate - might that work here?

I literally was chatting to someone this morning and planning what jewellery she was going to wear to a wedding with this exact same dress!

What's more - the wedding sounds exactly the same type she is going to. City, reg office, nice brasserie. Bride and groom in their late 30s/early 40s. Not sure what the bride is wearing but I could imagine her in trainers.

All I can say is, if this wedding is this Saturday coming you may find someone else wearing the same thing

Thank you all for replying and reassuring me, I will still have to work out the rest of the outfit but at least I've got a base that I really like and know I feel good in. Going to stick with flats I think, I have a lower back thing that gets aggravated by wearing heels and it's going to be a long day. I promise to wear something nice though, not my usual flip flops! The wedding is in June so hopefully not in danger of bumping into anyone wearing the same dress!
Oooh I'm envisaging a nice soft cream leather jacket now... But I don't own such a thing and I expect a nice one would be rather expensive!