I just did my first wedding cake. It could have been better but I tried my best.

The bride sent out about 100 invitations (I believe the exact total was 96), and received about 50 RSVP's back. I reasoned that about 75-90 guests would be attending (which about that did actually show!)

She ordered a cake seving 156 guests, even though I proposed a smaller one. I assured her that we would still have plenty of cake and that this amount was more reasonable, but she insisted on the 156 serving one.

How would I convince the bride next time (hopefully a different one) that a cake serving 116 would be a better option? Should I just keep my mouth shut and give her what she wants?

Hi, I always give them a few options. But if they insisting having exact number of servings they want, they need to pay for it. If they don't want your advice, that's fine. But need to pay for what she gets.

I also give them different options. You tried to tell her, but she didn't listen. Not your fault.

Give her several different options. And let her know that not everyone she invites is going to show up. I believe that you are supposed to plan for about 2/3 of the number of invitations you send out, to RSVP. And if she starts small and finds out that more people are coming, she can always call and increase the serving size of the cake (as long as she gives you more than 2 weeks notice). Which would of course make her total go up.

If she only invited 96 people and ordered cake for 150+, then she either wanted a larger cake for the look, or she wanted leftover cake for any number of reasons.

You advised her, she made her decision, take her check and enjoy the sale.

Sometimes brides just want the cake for the look or they want to take the top tier home tc. I recommend you put a clause in your contrat that says how many cake servings you suggested, how many guests are expected and how many servings the bride ordered. This way no one can claim you never told her she was ordering more than she needed.