“Thanks/Thank You”, doesn’t sound right to my ears, but I can’t really think of anything better. (There are worse possibilities of course; “Same to you” or “you too” probably being the worst I’ve heard).
What’s the Dope on this?
(If this is too frivolous for General Questions, feel free to move)
If you can’t think of anything better, and everybody else can’t think of anything better, I think we have a winner here.
But, in sympathy, for you and Moms everywhere, I always think the congratulations/pleasantry should be directed at one’s Mother.
“Thank you…but my birthday isn’t until September.”
You’re thanking them (in not so many words) for their consideration in remembering an anniversary that’s pretty important to you.
Works for me.
It’s against the rules here on the SDMB to post what I say … rhymes with ewe … my mother reminds me often enough about what she endured those 138 hours of hard labor …
“Thank you” is always the correct response when someone wishes you well in any form.
My significant other has trouble accepting these sorts of good wishes from others and feels like she needs to return the favor in some way. It’s not necessary. It’s a small pleasantry. Accept it nicely with a “Thank you” and move on.
‘boo’ ?
“Same to you!”.
“Happy birthday.”
“Thanks.”
Or, to generalize as OBob did:
“I wish you well.”
“Thank you.”
What’s wrong with that?
Snu-snu? Birthday snu-snu is de rigueur.
This is really a question in your mind? “Thanks” truly doesn’t sound right to you?
Maybe he’s saying it wrong. Maybe it comes out “tfhfaunkkkkkkshshshs”.
That wouldn’t sound right to me either.
mmm
I’m puzzled, as well. Of course, “thank you” (or some variant) is the usual response. Why the hell wouldn’t you say “thanks”?
I’ve had a classmate and two coworkers who’d been born on the exact same date as me (the coworkers, in the same job!). In that case, “and to you” is perfectly correct 
Thank you
Or
How nice you remembered!
I do feel somewhat similar to OP when someone compliments how pretty my dog, or, l’havdil,* my wife is. “Thank you” always seems like it shouldn’t be said by me.
*"L’havdil is a Hebrew word meaning “to separate”: it’s very useful stylistically at points in some sentences like this, and would be a nicety to have in English: when a distasteful term in itself or by comparison by literal juxtaposition is linked with another and you want to be sure that in this case of making some other point only, you can throw that in, without having to recast the sentence.
In these circumstances, why wouldn’t you say “I think so too”? If it’s your wife, you can add “I’ll tell her you said so”. Especially if it’s your wife, it is odd to respond with “thank you”.
How about an angry scowl and a shaking fist: “Don’t tell me what kind of birthday to have!”
“What’s so happy about it?”
She could always say “Thank you, and thank you for remembering” so they feel great about their memory skillz.