Warning: this might be the most irrelevant, how-many-angels-can-dance-on-the-head-of-a-pin thing you ever read in your life. But if you're a startup founder who is even slightly ADD about things grammar - maybe you'll relate.
See, once you've nailed your startup idea, gathered a founding team, grabbed the domain name and Twitter handle. What's next? Why, it's time to print some business cards and give yourself a title.
So assuming you've found a buddy to join your venture, what are you? A co-founder? A cofounder? Or maybe a Co-Founder?
Yes, you should care about the answer! What, think I'm crazy, well skip to the last line.
For every sane person who cares deeply about proper English usage (ahem), please read on.
1. What do the authorities say?
There's no guiding authority issuing hard and fast rules for English language usage (besides me sometimes). There are several prominent grammar guides telling you how to use your commas and semicolons, and style guides - steering you away from sins like passive voice, ahem.
According to English Language and Usage, co-founder is more British English, cofounder more American. Longman and Collins advocate less hyphens, while Chambers insists on hyphens.
The convention on Wikipedia is that you co-found, and you're a co-founder. Wikipedia has weight in how people read language these days, maybe more than Longman, Collins or Chambers.
2. What do people call themselves?
Just picked up a stack of business cards on my desk, harvested in London, Dublin, New York and Amsterdam. The results:
Co-founder / Co-Founder / CO-FOUNDER: 8
Cofounder: zero
People who are founders and don't use the phrase "Founder": 6
This one clearly weighs co-founder. That's what people are choosing to call themselves. Though you also see people - especially in the B2B space - moving away from "Founder" in their title altogether. Hubris avoiding? Trying to look less start-uppy?
3. What do Tech Blogs use?
The people who presumably have thought about this the most are the world's tech blogs, who write every day about us co/co-founders.
From my unscientific sampling (i.e. googling) of the leading tech blogs, co-founder is the winners here. Even googling "[publication name] cofounder" throws up instead a pile of links to stories about co-founder(s), with a dash (-).
The Verge seems to use co-founder pretty uniformly. TechCrunch too. Ditto All Things D. Same at The Next Web. Not sure how this consensus emerged, but it's strong.
CONCLUSION:
You're a co-founder. Take that little dash. Stick it in your title. And don't bother think about this ever again.