There's a spectrum of behaviors I could recommend here with more information on, say, where the startup is located (because your parents totally aren't insane if the answer is Tokyo) or what stage it is at. For a Valley startup, I think a suit might quite possibly say something about your culture fit that will not be judged in a positive manner, and might suggest anything in the middle of the Venn diagram a) makes you look good and b) could be warn in front of a friend's parents without giving offense in spite of having no prior knowledge of their views on appropriate attire.

If you're totally starved for ideas, for guys, khaki pants and a solid shirt, both ironed. I'm even less qualified for giving sartorial advice to ladies than I am to men, so I'll defer to someone else on that.

n.b. I fairly often do meetings with startup folks, including potential clients, in either that or my usual jeans + T-shirt with a track jacket on top uniform, and can't remember feeling conspicuously underdressed recently. (Edited to add: Ahh, forgot a conspicuous exception that proves the rule, but I can't disclose it without violating an NDA. Suffice it to say that if the industry a startup is in would make a blind ferret say "Dude, you should dress up for that" then you should probably dress up for that. Still got the engagement but went shopping before I started showing up on site.)

I usually just ask someone from the company I will be interviewing with.

IMO, a suit and tie, especially for a junior developer type position is probably wrong UNLESS you are the sort of person that is 100% comfortable and natural in a suit, and even then I'd skip the tie.

My goal would be to dress 1 step above the people you are interviewing with. Enough that you clothes help convey a sense of elevated status, but not so much they look at you and go "I don't want to work with some guy that wears a tuxedo to work".

Based on my non-scientific observations over the years, the ideal outfit would be pressed khakis, ironed polo or button-down shirt, sport-coat. If the environment is one where the people dress a little nicer, then you fit in well and the jacket probably sets you apart. If it's uber-casual you can leave the jacket someplace and then you'll be dressed nicely, but still a touch above most of the people you're interviewing with.

FWIW, I can't remember the last time I've work a suit to an interview in probably 15+ years, the last 10+ of that I've been working higher-level management type jobs, many times in sales-ish roles/departments.

Also, respect to your parents, but their conventional wisdom is probably massively out of date with current job trends/cultures, especially as it relates to developer positions.

It's definitely possible to dress up without looking like a stiff in a suit. Get a decent button down from somewhere like J Crew or Banana Republic, a pair of nice, dark jeans (or khakis) and some dark leather shoes. The key take-away is

  a suit doesn't necessarily = well-dressed
  no suit doesn't necessarily = not well-dressed

Think of your typical office drone (like the guys in Office Space) - they're in crappy suits and don't look that good. Likewise, some of the best-dressed people hardly ever wear strict "suits."

But, I do agree with the poster below: If a company balks because you overdressed for your interview it's their problem, not yours.

I have a rule that I will never wear a suit and a tie to interviews. I don't dress scruffily however nor do I dress formally. Some companies take offence at that and, in some cases, you won't get the job as a result. Those jobs though - chances are you don't want them.

However if in future I am ever struggling to find a job then I will likely have to relent on this rule.

I'll have to agree with this. As a programmer, I'm not particularly interested in wearing a suit and tie while working so by principle I wouldn't wear it to an interview.

It really depends on the company, though. If while talking with the company before the interview they came off as lax on their dress code, I wouldn't bother wearing anything fancy. I guess it's about judging the appropriateness for the given situation.

In the end, I'd prefer to wear whatever I'm most comfortable in so I can be myself and show them exactly who I am, as opposed to carbon copy office bitch in a suit.

For me it's not about the suit, it's about the rules. If a company requires you to wear a suit (by the way, I'm fine with wearing a suit for client meetings, etc) - chances are they'll be restrictive in other areas too.

I agree, plus it just sets a tone and atmosphere I don't want to work in.

Unfortunately, my present employer requires I wear a collared shirt and dress shoes, which I hate. I am much more productive when I can wear whatever I want. It shows, too. Especially when I'm forced to come in on a Saturday but can wear whatever I want; I get so much more done.

"I have a rule that I will never wear a suit and a tie to interviews." I like that rule but it unfortunately does not work for certain industries like finance, investment banking etc. where I work. Even if you go for a developer at one of thse banks, they expect you to be fully dressed. Heck, even during your actual work weeks once hired, we do no wear jeans on wall street (exceptions are there).

It certainly doesn't work for finance, etc - which is why I don't want to work in those industries! But yes, fair enough - I'm not saying it'll work for everyone.

Your parents are right. If a company balks because you overdressed for your interview it's their problem, not yours.

"I don't want to appear as a stiff who won't fit in with the culture."

I do not think that just by wearing a suit, you would give that impression. everyone understands that interviews are always a little more formal than the actual job. Even if the startup company where you will interview has dress code which includes shorts or jeans, I suggest you go in a simple business suit. The worst that could happen ? The interviewers will tell you that they are not that formal but thats ok. If you go without a suit, it may not hurt your chances either especially at a startup but why take a chance. My suggestion: go with a business suit. You have nothing to lose with that.

I've interviewed and secured something like five developer jobs in as many years, at both startupish and big-money companies. Jeans, t-shirt and hoodie at each.