I got into Y Combinator as a solo founder and left with a $4.5 million investment. Here's how I got in on my second try and what it was like.

• Kathryn Cross is the founder of Anja Health, a cord blood bank that freezes stem cells for future disease treatment purposes.
• Cross joined Silicon Valley's hottest startup accelerator, Y Combinator, in January 2022.

This as-told-to essay is based on a conversation with Kathryn Cross, the 23-year-old founder of Anja Health, based in Los Angeles, about her experience in Y Combinator. It has been edited for length and clarity.

I first heard about the startup accelerator Y Combinator when I was studying at Wellesley College and taking entrepreneurship classes at MIT. I found out more after graduating in January 2021 when I moved into Launch House, a coliving space for founders in Los Angeles.

I spent three months in the house building Anja Health, a personalized cord blood bank that freezes umbilical cord and placenta's stem cells for future disease treatment purposes, while working as an experience designer for digital-consulting company Publicis Sapient. Many of the founders living in the house were in Y Combinator, and they told me how beneficial it was.

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I didn't get a lot of exposure to the tech world at Wellesley, so I didn't feel fully equipped with the proper network, resources, or knowledge to run a successful startup. I felt I could find that in YC.

YC invests $125,000 in your company in return for 7%, and then it invests a further $375,000. I applied twice for YC and was accepted into the W22 batch, which ran from January to April 2022.

The first time I applied in February 2021, Anja Health was literally just an idea and barely a website. I left my job with Publicis Sapient in June 2021 to begin working full-time for Anja Health. The second time I applied during the summer of 2021, I had revenue, customers, a functioning website, and a supply chain.

I filled out an online form and added a short video in my application

The form included questions like, "What problem are you solving?" and "How big is your market?" I conveyed most of what I wanted to say about my startup in the application form. For the video portion, I just wanted to show how confident I was as a person. I wore bright colors to help me stand out and tried to speak with confidence.

The next stage was a 10-minute Zoom call with YC partners and entrepreneurs Jared Friedman, Nicolas Dessaigne, and Surbhi Sarna, whom I would have the opportunity to work with if I was accepted. They asked me about the science behind my company, what I thought about market size, and what motivates me as a founder.

I'd practiced quite a few of my answers with people who had been through YC, so I was prepared, but the interviews are notoriously very short, so I could've said more. When I received the call that I'd been accepted, I was delighted. Ninety percent of companies accepted to YC have cofounders, but I made it through as a solo founder.

When I was in YC, I would run my business from home as usual

My YC experience was virtual, so I completed it while living in Los Angeles. Each week I listened to online talks by successful founders of companies that went through YC like Airbnb and Stripe or experts in fields like SEO. I also connected with YC alumni via Bookface, YC's version of Facebook. I not only had my mentors at YC, but I was also mentored by the peers I was living with.

You only need to commit a few hours each week to the YC program. It's not a case of taking time off from your startup to attend the course, as they want you to work on your business and accelerate it. Each morning I would get up around 8 a.m., start work, and then have calls with a partner, whether that was Nicholas, Jared, or Surbhi.

The final part of the three-month course is Demo Day, when you present to more than 1,000 potential investors. A lot of them are former YC founders or partners. It's much less intimidating on Zoom than it is in person. I couldn't even see all the people in the room. While I was sitting in my living room looking at my laptop, I could only see my slides on a screen and me.

Presentations on Demo Day are so short, as each company has just one minute to speak, so it really doesn't require a ton of preparation. What you really have to prepare for is the fundraising that comes from Demo Day.

Over the 3 months you spend at YC, you learn everything from finding customers to fundraising

While I'd already raised $400,000 in a preseed round in the summer before I joined YC, the program, especially its coverage of the fundraising process, was still useful to me.

The first time I fundraised I felt I was just flailing because I didn't have any processes in place. The second time I fundraised was after I'd finished my YC course, and not only was I very intentional about whom I reached out to, but I also set timelines and tracked metrics, like the response rate. In the seed round, which ran from April to June 2022 and stemmed from Demo Day, I raised $4.5 million, and investors included Reddit's cofounder Alexis Ohanian.

My goal for fundraising was to grow the company and increase staffing levels. When I applied to YC, I was Anja Health's only member of staff. Now we're a team of five.

I still speak to my YC partners regularly. We have a group chat, and I message them on an as-needed basis. I probably could've achieved what I've done without YC, but it would've been a lot harder. In tech and the startup world, your network is your net worth, and YC is a really valuable network.

Did you go through Y Combinator and have a story to tell? Email Lauryn Haas at lhaas@insider.com.